1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
use super::*;
use crate::cmp::Ordering::{self, Equal, Greater, Less};
use crate::intrinsics;
use crate::slice::{self, SliceIndex};

impl<T: ?Sized> *mut T {
    /// Returns `true` if the pointer is null.
    ///
    /// Note that unsized types have many possible null pointers, as only the
    /// raw data pointer is considered, not their length, vtable, etc.
    /// Therefore, two pointers that are null may still not compare equal to
    /// each other.
    ///
    /// ## Behavior during const evaluation
    ///
    /// When this function is used during const evaluation, it may return `false` for pointers
    /// that turn out to be null at runtime. Specifically, when a pointer to some memory
    /// is offset beyond its bounds in such a way that the resulting pointer is null,
    /// the function will still return `false`. There is no way for CTFE to know
    /// the absolute position of that memory, so we cannot tell if the pointer is
    /// null or not.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut s = [1, 2, 3];
    /// let ptr: *mut u32 = s.as_mut_ptr();
    /// assert!(!ptr.is_null());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
    #[inline]
    pub const fn is_null(self) -> bool {
        // Compare via a cast to a thin pointer, so fat pointers are only
        // considering their "data" part for null-ness.
        match (self as *mut u8).guaranteed_eq(null_mut()) {
            None => false,
            Some(res) => res,
        }
    }

    /// Casts to a pointer of another type.
    #[stable(feature = "ptr_cast", since = "1.38.0")]
    #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
    #[inline(always)]
    pub const fn cast<U>(self) -> *mut U {
        self as _
    }

    /// Use the pointer value in a new pointer of another type.
    ///
    /// In case `val` is a (fat) pointer to an unsized type, this operation
    /// will ignore the pointer part, whereas for (thin) pointers to sized
    /// types, this has the same effect as a simple cast.
    ///
    /// The resulting pointer will have provenance of `self`, i.e., for a fat
    /// pointer, this operation is semantically the same as creating a new
    /// fat pointer with the data pointer value of `self` but the metadata of
    /// `val`.
    ///
    /// # Examples
    ///
    /// This function is primarily useful for allowing byte-wise pointer
    /// arithmetic on potentially fat pointers:
    ///
    /// ```
    /// #![feature(set_ptr_value)]
    /// # use core::fmt::Debug;
    /// let mut arr: [i32; 3] = [1, 2, 3];
    /// let mut ptr = arr.as_mut_ptr() as *mut dyn Debug;
    /// let thin = ptr as *mut u8;
    /// unsafe {
    ///     ptr = thin.add(8).with_metadata_of(ptr);
    ///     # assert_eq!(*(ptr as *mut i32), 3);
    ///     println!("{:?}", &*ptr); // will print "3"
    /// }
    /// ```
    #[unstable(feature = "set_ptr_value", issue = "75091")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[inline]
    pub fn with_metadata_of<U>(self, mut val: *mut U) -> *mut U
    where
        U: ?Sized,
    {
        let target = &mut val as *mut *mut U as *mut *mut u8;
        // SAFETY: In case of a thin pointer, this operations is identical
        // to a simple assignment. In case of a fat pointer, with the current
        // fat pointer layout implementation, the first field of such a
        // pointer is always the data pointer, which is likewise assigned.
        unsafe { *target = self as *mut u8 };
        val
    }

    /// Changes constness without changing the type.
    ///
    /// This is a bit safer than `as` because it wouldn't silently change the type if the code is
    /// refactored.
    ///
    /// While not strictly required (`*mut T` coerces to `*const T`), this is provided for symmetry
    /// with [`cast_mut`] on `*const T` and may have documentation value if used instead of implicit
    /// coercion.
    ///
    /// [`cast_mut`]: #method.cast_mut
    #[stable(feature = "ptr_const_cast", since = "1.65.0")]
    #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
    pub const fn cast_const(self) -> *const T {
        self as _
    }

    /// Casts a pointer to its raw bits.
    ///
    /// This is equivalent to `as usize`, but is more specific to enhance readability.
    /// The inverse method is [`from_bits`](#method.from_bits-1).
    ///
    /// In particular, `*p as usize` and `p as usize` will both compile for
    /// pointers to numeric types but do very different things, so using this
    /// helps emphasize that reading the bits was intentional.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_to_from_bits)]
    /// let mut array = [13, 42];
    /// let mut it = array.iter_mut();
    /// let p0: *mut i32 = it.next().unwrap();
    /// assert_eq!(<*mut _>::from_bits(p0.to_bits()), p0);
    /// let p1: *mut i32 = it.next().unwrap();
    /// assert_eq!(p1.to_bits() - p0.to_bits(), 4);
    /// ```
    #[unstable(feature = "ptr_to_from_bits", issue = "91126")]
    pub fn to_bits(self) -> usize
    where
        T: Sized,
    {
        self as usize
    }

    /// Creates a pointer from its raw bits.
    ///
    /// This is equivalent to `as *mut T`, but is more specific to enhance readability.
    /// The inverse method is [`to_bits`](#method.to_bits-1).
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_to_from_bits)]
    /// use std::ptr::NonNull;
    /// let dangling: *mut u8 = NonNull::dangling().as_ptr();
    /// assert_eq!(<*mut u8>::from_bits(1), dangling);
    /// ```
    #[unstable(feature = "ptr_to_from_bits", issue = "91126")]
    pub fn from_bits(bits: usize) -> Self
    where
        T: Sized,
    {
        bits as Self
    }

    /// Gets the "address" portion of the pointer.
    ///
    /// This is similar to `self as usize`, which semantically discards *provenance* and
    /// *address-space* information. However, unlike `self as usize`, casting the returned address
    /// back to a pointer yields [`invalid`][], which is undefined behavior to dereference. To
    /// properly restore the lost information and obtain a dereferenceable pointer, use
    /// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr].
    ///
    /// If using those APIs is not possible because there is no way to preserve a pointer with the
    /// required provenance, use [`expose_addr`][pointer::expose_addr] and
    /// [`from_exposed_addr_mut`][from_exposed_addr_mut] instead. However, note that this makes
    /// your code less portable and less amenable to tools that check for compliance with the Rust
    /// memory model.
    ///
    /// On most platforms this will produce a value with the same bytes as the original
    /// pointer, because all the bytes are dedicated to describing the address.
    /// Platforms which need to store additional information in the pointer may
    /// perform a change of representation to produce a value containing only the address
    /// portion of the pointer. What that means is up to the platform to define.
    ///
    /// This API and its claimed semantics are part of the Strict Provenance experiment, and as such
    /// might change in the future (including possibly weakening this so it becomes wholly
    /// equivalent to `self as usize`). See the [module documentation][crate::ptr] for details.
    #[must_use]
    #[inline]
    #[unstable(feature = "strict_provenance", issue = "95228")]
    pub fn addr(self) -> usize
    where
        T: Sized,
    {
        // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
        // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the
        // provenance).
        unsafe { mem::transmute(self) }
    }

    /// Gets the "address" portion of the pointer, and 'exposes' the "provenance" part for future
    /// use in [`from_exposed_addr`][].
    ///
    /// This is equivalent to `self as usize`, which semantically discards *provenance* and
    /// *address-space* information. Furthermore, this (like the `as` cast) has the implicit
    /// side-effect of marking the provenance as 'exposed', so on platforms that support it you can
    /// later call [`from_exposed_addr_mut`][] to reconstitute the original pointer including its
    /// provenance. (Reconstructing address space information, if required, is your responsibility.)
    ///
    /// Using this method means that code is *not* following Strict Provenance rules. Supporting
    /// [`from_exposed_addr_mut`][] complicates specification and reasoning and may not be supported
    /// by tools that help you to stay conformant with the Rust memory model, so it is recommended
    /// to use [`addr`][pointer::addr] wherever possible.
    ///
    /// On most platforms this will produce a value with the same bytes as the original pointer,
    /// because all the bytes are dedicated to describing the address. Platforms which need to store
    /// additional information in the pointer may not support this operation, since the 'expose'
    /// side-effect which is required for [`from_exposed_addr_mut`][] to work is typically not
    /// available.
    ///
    /// This API and its claimed semantics are part of the Strict Provenance experiment, see the
    /// [module documentation][crate::ptr] for details.
    ///
    /// [`from_exposed_addr_mut`]: from_exposed_addr_mut
    #[must_use]
    #[inline]
    #[unstable(feature = "strict_provenance", issue = "95228")]
    pub fn expose_addr(self) -> usize
    where
        T: Sized,
    {
        // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
        self as usize
    }

    /// Creates a new pointer with the given address.
    ///
    /// This performs the same operation as an `addr as ptr` cast, but copies
    /// the *address-space* and *provenance* of `self` to the new pointer.
    /// This allows us to dynamically preserve and propagate this important
    /// information in a way that is otherwise impossible with a unary cast.
    ///
    /// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset
    /// `self` to the given address, and therefore has all the same capabilities and restrictions.
    ///
    /// This API and its claimed semantics are part of the Strict Provenance experiment,
    /// see the [module documentation][crate::ptr] for details.
    #[must_use]
    #[inline]
    #[unstable(feature = "strict_provenance", issue = "95228")]
    pub fn with_addr(self, addr: usize) -> Self
    where
        T: Sized,
    {
        // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
        //
        // In the mean-time, this operation is defined to be "as if" it was
        // a wrapping_offset, so we can emulate it as such. This should properly
        // restore pointer provenance even under today's compiler.
        let self_addr = self.addr() as isize;
        let dest_addr = addr as isize;
        let offset = dest_addr.wrapping_sub(self_addr);

        // This is the canonical desugarring of this operation
        self.wrapping_byte_offset(offset)
    }

    /// Creates a new pointer by mapping `self`'s address to a new one.
    ///
    /// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details.
    ///
    /// This API and its claimed semantics are part of the Strict Provenance experiment,
    /// see the [module documentation][crate::ptr] for details.
    #[must_use]
    #[inline]
    #[unstable(feature = "strict_provenance", issue = "95228")]
    pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self
    where
        T: Sized,
    {
        self.with_addr(f(self.addr()))
    }

    /// Decompose a (possibly wide) pointer into its address and metadata components.
    ///
    /// The pointer can be later reconstructed with [`from_raw_parts_mut`].
    #[unstable(feature = "ptr_metadata", issue = "81513")]
    #[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
    #[inline]
    pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
        (self.cast(), super::metadata(self))
    }

    /// Returns `None` if the pointer is null, or else returns a shared reference to
    /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
    /// must be used instead.
    ///
    /// For the mutable counterpart see [`as_mut`].
    ///
    /// [`as_uninit_ref`]: #method.as_uninit_ref-1
    /// [`as_mut`]: #method.as_mut
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be properly aligned.
    ///
    /// * It must be "dereferenceable" in the sense defined in [the module documentation].
    ///
    /// * The pointer must point to an initialized instance of `T`.
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get mutated (except inside `UnsafeCell`).
    ///
    /// This applies even if the result of this method is unused!
    /// (The part about being initialized is not yet fully decided, but until
    /// it is, the only safe approach is to ensure that they are indeed initialized.)
    ///
    /// [the module documentation]: crate::ptr#safety
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
    ///
    /// unsafe {
    ///     if let Some(val_back) = ptr.as_ref() {
    ///         println!("We got back the value: {val_back}!");
    ///     }
    /// }
    /// ```
    ///
    /// # Null-unchecked version
    ///
    /// If you are sure the pointer can never be null and are looking for some kind of
    /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
    /// dereference the pointer directly.
    ///
    /// ```
    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
    ///
    /// unsafe {
    ///     let val_back = &*ptr;
    ///     println!("We got back the value: {val_back}!");
    /// }
    /// ```
    #[stable(feature = "ptr_as_ref", since = "1.9.0")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    #[inline]
    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
        // SAFETY: the caller must guarantee that `self` is valid for a
        // reference if it isn't null.
        if self.is_null() { None } else { unsafe { Some(&*self) } }
    }

    /// Returns `None` if the pointer is null, or else returns a shared reference to
    /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
    /// that the value has to be initialized.
    ///
    /// For the mutable counterpart see [`as_uninit_mut`].
    ///
    /// [`as_ref`]: #method.as_ref-1
    /// [`as_uninit_mut`]: #method.as_uninit_mut
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be properly aligned.
    ///
    /// * It must be "dereferenceable" in the sense defined in [the module documentation].
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get mutated (except inside `UnsafeCell`).
    ///
    /// This applies even if the result of this method is unused!
    ///
    /// [the module documentation]: crate::ptr#safety
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// #![feature(ptr_as_uninit)]
    ///
    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
    ///
    /// unsafe {
    ///     if let Some(val_back) = ptr.as_uninit_ref() {
    ///         println!("We got back the value: {}!", val_back.assume_init());
    ///     }
    /// }
    /// ```
    #[inline]
    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
    where
        T: Sized,
    {
        // SAFETY: the caller must guarantee that `self` meets all the
        // requirements for a reference.
        if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
    }

    /// Calculates the offset from a pointer.
    ///
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// If any of the following conditions are violated, the result is Undefined
    /// Behavior:
    ///
    /// * Both the starting and resulting pointer must be either in bounds or one
    ///   byte past the end of the same [allocated object].
    ///
    /// * The computed offset, **in bytes**, cannot overflow an `isize`.
    ///
    /// * The offset being in bounds cannot rely on "wrapping around" the address
    ///   space. That is, the infinite-precision sum, **in bytes** must fit in a usize.
    ///
    /// The compiler and standard library generally tries to ensure allocations
    /// never reach a size where an offset is a concern. For instance, `Vec`
    /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
    /// `vec.as_ptr().add(vec.len())` is always safe.
    ///
    /// Most platforms fundamentally can't even construct such an allocation.
    /// For instance, no known 64-bit platform can ever serve a request
    /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
    /// However, some 32-bit and 16-bit platforms may successfully serve a request for
    /// more than `isize::MAX` bytes with things like Physical Address
    /// Extension. As such, memory acquired directly from allocators or memory
    /// mapped files *may* be too large to handle with this function.
    ///
    /// Consider using [`wrapping_offset`] instead if these constraints are
    /// difficult to satisfy. The only advantage of this method is that it
    /// enables more aggressive compiler optimizations.
    ///
    /// [`wrapping_offset`]: #method.wrapping_offset
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut s = [1, 2, 3];
    /// let ptr: *mut u32 = s.as_mut_ptr();
    ///
    /// unsafe {
    ///     println!("{}", *ptr.offset(1));
    ///     println!("{}", *ptr.offset(2));
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn offset(self, count: isize) -> *mut T
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `offset`.
        // The obtained pointer is valid for writes since the caller must
        // guarantee that it points to the same allocated object as `self`.
        unsafe { intrinsics::offset(self, count) as *mut T }
    }

    /// Calculates the offset from a pointer in bytes.
    ///
    /// `count` is in units of **bytes**.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [offset][pointer::offset] on it. See that method for documentation
    /// and safety requirements.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn byte_offset(self, count: isize) -> Self {
        // SAFETY: the caller must uphold the safety contract for `offset`.
        let this = unsafe { self.cast::<u8>().offset(count).cast::<()>() };
        from_raw_parts_mut::<T>(this, metadata(self))
    }

    /// Calculates the offset from a pointer using wrapping arithmetic.
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// This operation itself is always safe, but using the resulting pointer is not.
    ///
    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
    /// be used to read or write other allocated objects.
    ///
    /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
    /// `x` and `y` point into the same allocated object.
    ///
    /// Compared to [`offset`], this method basically delays the requirement of staying within the
    /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
    /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
    /// can be optimized better and is thus preferable in performance-sensitive code.
    ///
    /// The delayed check only considers the value of the pointer that was dereferenced, not the
    /// intermediate values used during the computation of the final result. For example,
    /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
    /// words, leaving the allocated object and then re-entering it later is permitted.
    ///
    /// [`offset`]: #method.offset
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // Iterate using a raw pointer in increments of two elements
    /// let mut data = [1u8, 2, 3, 4, 5];
    /// let mut ptr: *mut u8 = data.as_mut_ptr();
    /// let step = 2;
    /// let end_rounded_up = ptr.wrapping_offset(6);
    ///
    /// while ptr != end_rounded_up {
    ///     unsafe {
    ///         *ptr = 0;
    ///     }
    ///     ptr = ptr.wrapping_offset(step);
    /// }
    /// assert_eq!(&data, &[0, 2, 0, 4, 0]);
    /// ```
    #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline(always)]
    pub const fn wrapping_offset(self, count: isize) -> *mut T
    where
        T: Sized,
    {
        // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
        unsafe { intrinsics::arith_offset(self, count) as *mut T }
    }

    /// Calculates the offset from a pointer in bytes using wrapping arithmetic.
    ///
    /// `count` is in units of **bytes**.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [wrapping_offset][pointer::wrapping_offset] on it. See that method
    /// for documentation.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    pub const fn wrapping_byte_offset(self, count: isize) -> Self {
        from_raw_parts_mut::<T>(
            self.cast::<u8>().wrapping_offset(count).cast::<()>(),
            metadata(self),
        )
    }

    /// Masks out bits of the pointer according to a mask.
    ///
    /// This is convenience for `ptr.map_addr(|a| a & mask)`.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[cfg(not(bootstrap))]
    #[unstable(feature = "ptr_mask", issue = "98290")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[inline(always)]
    pub fn mask(self, mask: usize) -> *mut T {
        let this = intrinsics::ptr_mask(self.cast::<()>(), mask) as *mut ();
        from_raw_parts_mut::<T>(this, metadata(self))
    }

    /// Returns `None` if the pointer is null, or else returns a unique reference to
    /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
    /// must be used instead.
    ///
    /// For the shared counterpart see [`as_ref`].
    ///
    /// [`as_uninit_mut`]: #method.as_uninit_mut
    /// [`as_ref`]: #method.as_ref-1
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be properly aligned.
    ///
    /// * It must be "dereferenceable" in the sense defined in [the module documentation].
    ///
    /// * The pointer must point to an initialized instance of `T`.
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get accessed (read or written) through any other pointer.
    ///
    /// This applies even if the result of this method is unused!
    /// (The part about being initialized is not yet fully decided, but until
    /// it is, the only safe approach is to ensure that they are indeed initialized.)
    ///
    /// [the module documentation]: crate::ptr#safety
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut s = [1, 2, 3];
    /// let ptr: *mut u32 = s.as_mut_ptr();
    /// let first_value = unsafe { ptr.as_mut().unwrap() };
    /// *first_value = 4;
    /// # assert_eq!(s, [4, 2, 3]);
    /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
    /// ```
    ///
    /// # Null-unchecked version
    ///
    /// If you are sure the pointer can never be null and are looking for some kind of
    /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
    /// you can dereference the pointer directly.
    ///
    /// ```
    /// let mut s = [1, 2, 3];
    /// let ptr: *mut u32 = s.as_mut_ptr();
    /// let first_value = unsafe { &mut *ptr };
    /// *first_value = 4;
    /// # assert_eq!(s, [4, 2, 3]);
    /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
    /// ```
    #[stable(feature = "ptr_as_ref", since = "1.9.0")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    #[inline]
    pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
        // SAFETY: the caller must guarantee that `self` is be valid for
        // a mutable reference if it isn't null.
        if self.is_null() { None } else { unsafe { Some(&mut *self) } }
    }

    /// Returns `None` if the pointer is null, or else returns a unique reference to
    /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
    /// that the value has to be initialized.
    ///
    /// For the shared counterpart see [`as_uninit_ref`].
    ///
    /// [`as_mut`]: #method.as_mut
    /// [`as_uninit_ref`]: #method.as_uninit_ref-1
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be properly aligned.
    ///
    /// * It must be "dereferenceable" in the sense defined in [the module documentation].
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get accessed (read or written) through any other pointer.
    ///
    /// This applies even if the result of this method is unused!
    ///
    /// [the module documentation]: crate::ptr#safety
    #[inline]
    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
    where
        T: Sized,
    {
        // SAFETY: the caller must guarantee that `self` meets all the
        // requirements for a reference.
        if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
    }

    /// Returns whether two pointers are guaranteed to be equal.
    ///
    /// At runtime this function behaves like `Some(self == other)`.
    /// However, in some contexts (e.g., compile-time evaluation),
    /// it is not always possible to determine equality of two pointers, so this function may
    /// spuriously return `None` for pointers that later actually turn out to have its equality known.
    /// But when it returns `Some`, the pointers' equality is guaranteed to be known.
    ///
    /// The return value may change from `Some` to `None` and vice versa depending on the compiler
    /// version and unsafe code must not
    /// rely on the result of this function for soundness. It is suggested to only use this function
    /// for performance optimizations where spurious `None` return values by this function do not
    /// affect the outcome, but just the performance.
    /// The consequences of using this method to make runtime and compile-time code behave
    /// differently have not been explored. This method should not be used to introduce such
    /// differences, and it should also not be stabilized before we have a better understanding
    /// of this issue.
    #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
    #[inline]
    pub const fn guaranteed_eq(self, other: *mut T) -> Option<bool>
    where
        T: Sized,
    {
        (self as *const T).guaranteed_eq(other as _)
    }

    /// Returns whether two pointers are guaranteed to be inequal.
    ///
    /// At runtime this function behaves like `Some(self == other)`.
    /// However, in some contexts (e.g., compile-time evaluation),
    /// it is not always possible to determine inequality of two pointers, so this function may
    /// spuriously return `None` for pointers that later actually turn out to have its inequality known.
    /// But when it returns `Some`, the pointers' inequality is guaranteed to be known.
    ///
    /// The return value may change from `Some` to `None` and vice versa depending on the compiler
    /// version and unsafe code must not
    /// rely on the result of this function for soundness. It is suggested to only use this function
    /// for performance optimizations where spurious `None` return values by this function do not
    /// affect the outcome, but just the performance.
    /// The consequences of using this method to make runtime and compile-time code behave
    /// differently have not been explored. This method should not be used to introduce such
    /// differences, and it should also not be stabilized before we have a better understanding
    /// of this issue.
    #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
    #[inline]
    pub const fn guaranteed_ne(self, other: *mut T) -> Option<bool>
    where
        T: Sized,
    {
        (self as *const T).guaranteed_ne(other as _)
    }

    /// Calculates the distance between two pointers. The returned value is in
    /// units of T: the distance in bytes divided by `mem::size_of::<T>()`.
    ///
    /// This function is the inverse of [`offset`].
    ///
    /// [`offset`]: #method.offset-1
    ///
    /// # Safety
    ///
    /// If any of the following conditions are violated, the result is Undefined
    /// Behavior:
    ///
    /// * Both the starting and other pointer must be either in bounds or one
    ///   byte past the end of the same [allocated object].
    ///
    /// * Both pointers must be *derived from* a pointer to the same object.
    ///   (See below for an example.)
    ///
    /// * The distance between the pointers, in bytes, must be an exact multiple
    ///   of the size of `T`.
    ///
    /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`.
    ///
    /// * The distance being in bounds cannot rely on "wrapping around" the address space.
    ///
    /// Rust types are never larger than `isize::MAX` and Rust allocations never wrap around the
    /// address space, so two pointers within some value of any Rust type `T` will always satisfy
    /// the last two conditions. The standard library also generally ensures that allocations
    /// never reach a size where an offset is a concern. For instance, `Vec` and `Box` ensure they
    /// never allocate more than `isize::MAX` bytes, so `ptr_into_vec.offset_from(vec.as_ptr())`
    /// always satisfies the last two conditions.
    ///
    /// Most platforms fundamentally can't even construct such a large allocation.
    /// For instance, no known 64-bit platform can ever serve a request
    /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
    /// However, some 32-bit and 16-bit platforms may successfully serve a request for
    /// more than `isize::MAX` bytes with things like Physical Address
    /// Extension. As such, memory acquired directly from allocators or memory
    /// mapped files *may* be too large to handle with this function.
    /// (Note that [`offset`] and [`add`] also have a similar limitation and hence cannot be used on
    /// such large allocations either.)
    ///
    /// [`add`]: #method.add
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Panics
    ///
    /// This function panics if `T` is a Zero-Sized Type ("ZST").
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut a = [0; 5];
    /// let ptr1: *mut i32 = &mut a[1];
    /// let ptr2: *mut i32 = &mut a[3];
    /// unsafe {
    ///     assert_eq!(ptr2.offset_from(ptr1), 2);
    ///     assert_eq!(ptr1.offset_from(ptr2), -2);
    ///     assert_eq!(ptr1.offset(2), ptr2);
    ///     assert_eq!(ptr2.offset(-2), ptr1);
    /// }
    /// ```
    ///
    /// *Incorrect* usage:
    ///
    /// ```rust,no_run
    /// let ptr1 = Box::into_raw(Box::new(0u8));
    /// let ptr2 = Box::into_raw(Box::new(1u8));
    /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
    /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1.
    /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff);
    /// assert_eq!(ptr2 as usize, ptr2_other as usize);
    /// // Since ptr2_other and ptr2 are derived from pointers to different objects,
    /// // computing their offset is undefined behavior, even though
    /// // they point to the same address!
    /// unsafe {
    ///     let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior
    /// }
    /// ```
    #[stable(feature = "ptr_offset_from", since = "1.47.0")]
    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn offset_from(self, origin: *const T) -> isize
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `offset_from`.
        unsafe { (self as *const T).offset_from(origin) }
    }

    /// Calculates the distance between two pointers. The returned value is in
    /// units of **bytes**.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [offset_from][pointer::offset_from] on it. See that method for
    /// documentation and safety requirements.
    ///
    /// For non-`Sized` pointees this operation considers only the data pointers,
    /// ignoring the metadata.
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn byte_offset_from(self, origin: *const T) -> isize {
        // SAFETY: the caller must uphold the safety contract for `offset_from`.
        unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
    }

    /// Calculates the distance between two pointers, *where it's known that
    /// `self` is equal to or greater than `origin`*. The returned value is in
    /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
    ///
    /// This computes the same value that [`offset_from`](#method.offset_from)
    /// would compute, but with the added precondition that that the offset is
    /// guaranteed to be non-negative.  This method is equivalent to
    /// `usize::from(self.offset_from(origin)).unwrap_unchecked()`,
    /// but it provides slightly more information to the optimizer, which can
    /// sometimes allow it to optimize slightly better with some backends.
    ///
    /// This method can be though of as recovering the `count` that was passed
    /// to [`add`](#method.add) (or, with the parameters in the other order,
    /// to [`sub`](#method.sub)).  The following are all equivalent, assuming
    /// that their safety preconditions are met:
    /// ```rust
    /// # #![feature(ptr_sub_ptr)]
    /// # unsafe fn blah(ptr: *mut i32, origin: *mut i32, count: usize) -> bool {
    /// ptr.sub_ptr(origin) == count
    /// # &&
    /// origin.add(count) == ptr
    /// # &&
    /// ptr.sub(count) == origin
    /// # }
    /// ```
    ///
    /// # Safety
    ///
    /// - The distance between the pointers must be non-negative (`self >= origin`)
    ///
    /// - *All* the safety conditions of [`offset_from`](#method.offset_from)
    ///   apply to this method as well; see it for the full details.
    ///
    /// Importantly, despite the return type of this method being able to represent
    /// a larger offset, it's still *not permitted* to pass pointers which differ
    /// by more than `isize::MAX` *bytes*.  As such, the result of this method will
    /// always be less than or equal to `isize::MAX as usize`.
    ///
    /// # Panics
    ///
    /// This function panics if `T` is a Zero-Sized Type ("ZST").
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_sub_ptr)]
    ///
    /// let mut a = [0; 5];
    /// let p: *mut i32 = a.as_mut_ptr();
    /// unsafe {
    ///     let ptr1: *mut i32 = p.add(1);
    ///     let ptr2: *mut i32 = p.add(3);
    ///
    ///     assert_eq!(ptr2.sub_ptr(ptr1), 2);
    ///     assert_eq!(ptr1.add(2), ptr2);
    ///     assert_eq!(ptr2.sub(2), ptr1);
    ///     assert_eq!(ptr2.sub_ptr(ptr2), 0);
    /// }
    ///
    /// // This would be incorrect, as the pointers are not correctly ordered:
    /// // ptr1.offset_from(ptr2)
    #[unstable(feature = "ptr_sub_ptr", issue = "95892")]
    #[rustc_const_unstable(feature = "const_ptr_sub_ptr", issue = "95892")]
    #[inline]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn sub_ptr(self, origin: *const T) -> usize
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `sub_ptr`.
        unsafe { (self as *const T).sub_ptr(origin) }
    }

    /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
    ///
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// If any of the following conditions are violated, the result is Undefined
    /// Behavior:
    ///
    /// * Both the starting and resulting pointer must be either in bounds or one
    ///   byte past the end of the same [allocated object].
    ///
    /// * The computed offset, **in bytes**, cannot overflow an `isize`.
    ///
    /// * The offset being in bounds cannot rely on "wrapping around" the address
    ///   space. That is, the infinite-precision sum must fit in a `usize`.
    ///
    /// The compiler and standard library generally tries to ensure allocations
    /// never reach a size where an offset is a concern. For instance, `Vec`
    /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
    /// `vec.as_ptr().add(vec.len())` is always safe.
    ///
    /// Most platforms fundamentally can't even construct such an allocation.
    /// For instance, no known 64-bit platform can ever serve a request
    /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
    /// However, some 32-bit and 16-bit platforms may successfully serve a request for
    /// more than `isize::MAX` bytes with things like Physical Address
    /// Extension. As such, memory acquired directly from allocators or memory
    /// mapped files *may* be too large to handle with this function.
    ///
    /// Consider using [`wrapping_add`] instead if these constraints are
    /// difficult to satisfy. The only advantage of this method is that it
    /// enables more aggressive compiler optimizations.
    ///
    /// [`wrapping_add`]: #method.wrapping_add
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let s: &str = "123";
    /// let ptr: *const u8 = s.as_ptr();
    ///
    /// unsafe {
    ///     println!("{}", *ptr.add(1) as char);
    ///     println!("{}", *ptr.add(2) as char);
    /// }
    /// ```
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn add(self, count: usize) -> Self
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `offset`.
        unsafe { self.offset(count as isize) }
    }

    /// Calculates the offset from a pointer in bytes (convenience for `.byte_offset(count as isize)`).
    ///
    /// `count` is in units of bytes.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [add][pointer::add] on it. See that method for documentation
    /// and safety requirements.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn byte_add(self, count: usize) -> Self {
        // SAFETY: the caller must uphold the safety contract for `add`.
        let this = unsafe { self.cast::<u8>().add(count).cast::<()>() };
        from_raw_parts_mut::<T>(this, metadata(self))
    }

    /// Calculates the offset from a pointer (convenience for
    /// `.offset((count as isize).wrapping_neg())`).
    ///
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// If any of the following conditions are violated, the result is Undefined
    /// Behavior:
    ///
    /// * Both the starting and resulting pointer must be either in bounds or one
    ///   byte past the end of the same [allocated object].
    ///
    /// * The computed offset cannot exceed `isize::MAX` **bytes**.
    ///
    /// * The offset being in bounds cannot rely on "wrapping around" the address
    ///   space. That is, the infinite-precision sum must fit in a usize.
    ///
    /// The compiler and standard library generally tries to ensure allocations
    /// never reach a size where an offset is a concern. For instance, `Vec`
    /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so
    /// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe.
    ///
    /// Most platforms fundamentally can't even construct such an allocation.
    /// For instance, no known 64-bit platform can ever serve a request
    /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space.
    /// However, some 32-bit and 16-bit platforms may successfully serve a request for
    /// more than `isize::MAX` bytes with things like Physical Address
    /// Extension. As such, memory acquired directly from allocators or memory
    /// mapped files *may* be too large to handle with this function.
    ///
    /// Consider using [`wrapping_sub`] instead if these constraints are
    /// difficult to satisfy. The only advantage of this method is that it
    /// enables more aggressive compiler optimizations.
    ///
    /// [`wrapping_sub`]: #method.wrapping_sub
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let s: &str = "123";
    ///
    /// unsafe {
    ///     let end: *const u8 = s.as_ptr().add(3);
    ///     println!("{}", *end.sub(1) as char);
    ///     println!("{}", *end.sub(2) as char);
    /// }
    /// ```
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn sub(self, count: usize) -> Self
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `offset`.
        unsafe { self.offset((count as isize).wrapping_neg()) }
    }

    /// Calculates the offset from a pointer in bytes (convenience for
    /// `.byte_offset((count as isize).wrapping_neg())`).
    ///
    /// `count` is in units of bytes.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [sub][pointer::sub] on it. See that method for documentation
    /// and safety requirements.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn byte_sub(self, count: usize) -> Self {
        // SAFETY: the caller must uphold the safety contract for `sub`.
        let this = unsafe { self.cast::<u8>().sub(count).cast::<()>() };
        from_raw_parts_mut::<T>(this, metadata(self))
    }

    /// Calculates the offset from a pointer using wrapping arithmetic.
    /// (convenience for `.wrapping_offset(count as isize)`)
    ///
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// This operation itself is always safe, but using the resulting pointer is not.
    ///
    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
    /// be used to read or write other allocated objects.
    ///
    /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
    /// `x` and `y` point into the same allocated object.
    ///
    /// Compared to [`add`], this method basically delays the requirement of staying within the
    /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
    /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
    /// can be optimized better and is thus preferable in performance-sensitive code.
    ///
    /// The delayed check only considers the value of the pointer that was dereferenced, not the
    /// intermediate values used during the computation of the final result. For example,
    /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
    /// allocated object and then re-entering it later is permitted.
    ///
    /// [`add`]: #method.add
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // Iterate using a raw pointer in increments of two elements
    /// let data = [1u8, 2, 3, 4, 5];
    /// let mut ptr: *const u8 = data.as_ptr();
    /// let step = 2;
    /// let end_rounded_up = ptr.wrapping_add(6);
    ///
    /// // This loop prints "1, 3, 5, "
    /// while ptr != end_rounded_up {
    ///     unsafe {
    ///         print!("{}, ", *ptr);
    ///     }
    ///     ptr = ptr.wrapping_add(step);
    /// }
    /// ```
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline(always)]
    pub const fn wrapping_add(self, count: usize) -> Self
    where
        T: Sized,
    {
        self.wrapping_offset(count as isize)
    }

    /// Calculates the offset from a pointer in bytes using wrapping arithmetic.
    /// (convenience for `.wrapping_byte_offset(count as isize)`)
    ///
    /// `count` is in units of bytes.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    pub const fn wrapping_byte_add(self, count: usize) -> Self {
        from_raw_parts_mut::<T>(self.cast::<u8>().wrapping_add(count).cast::<()>(), metadata(self))
    }

    /// Calculates the offset from a pointer using wrapping arithmetic.
    /// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`)
    ///
    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
    /// offset of `3 * size_of::<T>()` bytes.
    ///
    /// # Safety
    ///
    /// This operation itself is always safe, but using the resulting pointer is not.
    ///
    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
    /// be used to read or write other allocated objects.
    ///
    /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
    /// `x` and `y` point into the same allocated object.
    ///
    /// Compared to [`sub`], this method basically delays the requirement of staying within the
    /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
    /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
    /// can be optimized better and is thus preferable in performance-sensitive code.
    ///
    /// The delayed check only considers the value of the pointer that was dereferenced, not the
    /// intermediate values used during the computation of the final result. For example,
    /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
    /// allocated object and then re-entering it later is permitted.
    ///
    /// [`sub`]: #method.sub
    /// [allocated object]: crate::ptr#allocated-object
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // Iterate using a raw pointer in increments of two elements (backwards)
    /// let data = [1u8, 2, 3, 4, 5];
    /// let mut ptr: *const u8 = data.as_ptr();
    /// let start_rounded_down = ptr.wrapping_sub(2);
    /// ptr = ptr.wrapping_add(4);
    /// let step = 2;
    /// // This loop prints "5, 3, 1, "
    /// while ptr != start_rounded_down {
    ///     unsafe {
    ///         print!("{}, ", *ptr);
    ///     }
    ///     ptr = ptr.wrapping_sub(step);
    /// }
    /// ```
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[must_use = "returns a new pointer rather than modifying its argument"]
    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
    #[inline]
    pub const fn wrapping_sub(self, count: usize) -> Self
    where
        T: Sized,
    {
        self.wrapping_offset((count as isize).wrapping_neg())
    }

    /// Calculates the offset from a pointer in bytes using wrapping arithmetic.
    /// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`)
    ///
    /// `count` is in units of bytes.
    ///
    /// This is purely a convenience for casting to a `u8` pointer and
    /// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation.
    ///
    /// For non-`Sized` pointees this operation changes only the data pointer,
    /// leaving the metadata untouched.
    #[must_use]
    #[inline(always)]
    #[unstable(feature = "pointer_byte_offsets", issue = "96283")]
    #[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
    pub const fn wrapping_byte_sub(self, count: usize) -> Self {
        from_raw_parts_mut::<T>(self.cast::<u8>().wrapping_sub(count).cast::<()>(), metadata(self))
    }

    /// Reads the value from `self` without moving it. This leaves the
    /// memory in `self` unchanged.
    ///
    /// See [`ptr::read`] for safety concerns and examples.
    ///
    /// [`ptr::read`]: crate::ptr::read()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn read(self) -> T
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for ``.
        unsafe { read(self) }
    }

    /// Performs a volatile read of the value from `self` without moving it. This
    /// leaves the memory in `self` unchanged.
    ///
    /// Volatile operations are intended to act on I/O memory, and are guaranteed
    /// to not be elided or reordered by the compiler across other volatile
    /// operations.
    ///
    /// See [`ptr::read_volatile`] for safety concerns and examples.
    ///
    /// [`ptr::read_volatile`]: crate::ptr::read_volatile()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub unsafe fn read_volatile(self) -> T
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `read_volatile`.
        unsafe { read_volatile(self) }
    }

    /// Reads the value from `self` without moving it. This leaves the
    /// memory in `self` unchanged.
    ///
    /// Unlike `read`, the pointer may be unaligned.
    ///
    /// See [`ptr::read_unaligned`] for safety concerns and examples.
    ///
    /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn read_unaligned(self) -> T
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `read_unaligned`.
        unsafe { read_unaligned(self) }
    }

    /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
    /// and destination may overlap.
    ///
    /// NOTE: this has the *same* argument order as [`ptr::copy`].
    ///
    /// See [`ptr::copy`] for safety concerns and examples.
    ///
    /// [`ptr::copy`]: crate::ptr::copy()
    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn copy_to(self, dest: *mut T, count: usize)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `copy`.
        unsafe { copy(self, dest, count) }
    }

    /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
    /// and destination may *not* overlap.
    ///
    /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
    ///
    /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
    ///
    /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
        unsafe { copy_nonoverlapping(self, dest, count) }
    }

    /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
    /// and destination may overlap.
    ///
    /// NOTE: this has the *opposite* argument order of [`ptr::copy`].
    ///
    /// See [`ptr::copy`] for safety concerns and examples.
    ///
    /// [`ptr::copy`]: crate::ptr::copy()
    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn copy_from(self, src: *const T, count: usize)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `copy`.
        unsafe { copy(src, self, count) }
    }

    /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
    /// and destination may *not* overlap.
    ///
    /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
    ///
    /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
    ///
    /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
        unsafe { copy_nonoverlapping(src, self, count) }
    }

    /// Executes the destructor (if any) of the pointed-to value.
    ///
    /// See [`ptr::drop_in_place`] for safety concerns and examples.
    ///
    /// [`ptr::drop_in_place`]: crate::ptr::drop_in_place()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    pub unsafe fn drop_in_place(self) {
        // SAFETY: the caller must uphold the safety contract for `drop_in_place`.
        unsafe { drop_in_place(self) }
    }

    /// Overwrites a memory location with the given value without reading or
    /// dropping the old value.
    ///
    /// See [`ptr::write`] for safety concerns and examples.
    ///
    /// [`ptr::write`]: crate::ptr::write()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn write(self, val: T)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `write`.
        unsafe { write(self, val) }
    }

    /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
    /// bytes of memory starting at `self` to `val`.
    ///
    /// See [`ptr::write_bytes`] for safety concerns and examples.
    ///
    /// [`ptr::write_bytes`]: crate::ptr::write_bytes()
    #[doc(alias = "memset")]
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn write_bytes(self, val: u8, count: usize)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `write_bytes`.
        unsafe { write_bytes(self, val, count) }
    }

    /// Performs a volatile write of a memory location with the given value without
    /// reading or dropping the old value.
    ///
    /// Volatile operations are intended to act on I/O memory, and are guaranteed
    /// to not be elided or reordered by the compiler across other volatile
    /// operations.
    ///
    /// See [`ptr::write_volatile`] for safety concerns and examples.
    ///
    /// [`ptr::write_volatile`]: crate::ptr::write_volatile()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub unsafe fn write_volatile(self, val: T)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `write_volatile`.
        unsafe { write_volatile(self, val) }
    }

    /// Overwrites a memory location with the given value without reading or
    /// dropping the old value.
    ///
    /// Unlike `write`, the pointer may be unaligned.
    ///
    /// See [`ptr::write_unaligned`] for safety concerns and examples.
    ///
    /// [`ptr::write_unaligned`]: crate::ptr::write_unaligned()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
    #[inline(always)]
    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    pub const unsafe fn write_unaligned(self, val: T)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `write_unaligned`.
        unsafe { write_unaligned(self, val) }
    }

    /// Replaces the value at `self` with `src`, returning the old
    /// value, without dropping either.
    ///
    /// See [`ptr::replace`] for safety concerns and examples.
    ///
    /// [`ptr::replace`]: crate::ptr::replace()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[inline(always)]
    pub unsafe fn replace(self, src: T) -> T
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `replace`.
        unsafe { replace(self, src) }
    }

    /// Swaps the values at two mutable locations of the same type, without
    /// deinitializing either. They may overlap, unlike `mem::swap` which is
    /// otherwise equivalent.
    ///
    /// See [`ptr::swap`] for safety concerns and examples.
    ///
    /// [`ptr::swap`]: crate::ptr::swap()
    #[stable(feature = "pointer_methods", since = "1.26.0")]
    #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
    #[inline(always)]
    pub const unsafe fn swap(self, with: *mut T)
    where
        T: Sized,
    {
        // SAFETY: the caller must uphold the safety contract for `swap`.
        unsafe { swap(self, with) }
    }

    /// Computes the offset that needs to be applied to the pointer in order to make it aligned to
    /// `align`.
    ///
    /// If it is not possible to align the pointer, the implementation returns
    /// `usize::MAX`. It is permissible for the implementation to *always*
    /// return `usize::MAX`. Only your algorithm's performance can depend
    /// on getting a usable offset here, not its correctness.
    ///
    /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
    /// used with the `wrapping_add` method.
    ///
    /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
    /// beyond the allocation that the pointer points into. It is up to the caller to ensure that
    /// the returned offset is correct in all terms other than alignment.
    ///
    /// # Panics
    ///
    /// The function panics if `align` is not a power-of-two.
    ///
    /// # Examples
    ///
    /// Accessing adjacent `u8` as `u16`
    ///
    /// ```
    /// use std::mem::align_of;
    ///
    /// # unsafe {
    /// let mut x = [5_u8, 6, 7, 8, 9];
    /// let ptr = x.as_mut_ptr();
    /// let offset = ptr.align_offset(align_of::<u16>());
    ///
    /// if offset < x.len() - 1 {
    ///     let u16_ptr = ptr.add(offset).cast::<u16>();
    ///     *u16_ptr = 0;
    ///
    ///     assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]);
    /// } else {
    ///     // while the pointer can be aligned via `offset`, it would point
    ///     // outside the allocation
    /// }
    /// # }
    /// ```
    #[stable(feature = "align_offset", since = "1.36.0")]
    #[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
    pub const fn align_offset(self, align: usize) -> usize
    where
        T: Sized,
    {
        if !align.is_power_of_two() {
            panic!("align_offset: align is not a power-of-two");
        }

        fn rt_impl<T>(p: *mut T, align: usize) -> usize {
            // SAFETY: `align` has been checked to be a power of 2 above
            unsafe { align_offset(p, align) }
        }

        const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
            usize::MAX
        }

        // SAFETY:
        // It is permissible for `align_offset` to always return `usize::MAX`,
        // algorithm correctness can not depend on `align_offset` returning non-max values.
        //
        // As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
        unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
    }

    /// Returns whether the pointer is properly aligned for `T`.
    #[must_use]
    #[inline]
    #[unstable(feature = "pointer_is_aligned", issue = "96284")]
    pub fn is_aligned(self) -> bool
    where
        T: Sized,
    {
        self.is_aligned_to(core::mem::align_of::<T>())
    }

    /// Returns whether the pointer is aligned to `align`.
    ///
    /// For non-`Sized` pointees this operation considers only the data pointer,
    /// ignoring the metadata.
    ///
    /// # Panics
    ///
    /// The function panics if `align` is not a power-of-two (this includes 0).
    #[must_use]
    #[inline]
    #[unstable(feature = "pointer_is_aligned", issue = "96284")]
    pub fn is_aligned_to(self, align: usize) -> bool {
        if !align.is_power_of_two() {
            panic!("is_aligned_to: align is not a power-of-two");
        }

        // Cast is needed for `T: !Sized`
        self.cast::<u8>().addr() & align - 1 == 0
    }
}

impl<T> *mut [T] {
    /// Returns the length of a raw slice.
    ///
    /// The returned value is the number of **elements**, not the number of bytes.
    ///
    /// This function is safe, even when the raw slice cannot be cast to a slice
    /// reference because the pointer is null or unaligned.
    ///
    /// # Examples
    ///
    /// ```rust
    /// #![feature(slice_ptr_len)]
    /// use std::ptr;
    ///
    /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
    /// assert_eq!(slice.len(), 3);
    /// ```
    #[inline(always)]
    #[unstable(feature = "slice_ptr_len", issue = "71146")]
    #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
    pub const fn len(self) -> usize {
        metadata(self)
    }

    /// Returns `true` if the raw slice has a length of 0.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(slice_ptr_len)]
    ///
    /// let mut a = [1, 2, 3];
    /// let ptr = &mut a as *mut [_];
    /// assert!(!ptr.is_empty());
    /// ```
    #[inline(always)]
    #[unstable(feature = "slice_ptr_len", issue = "71146")]
    #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
    pub const fn is_empty(self) -> bool {
        self.len() == 0
    }

    /// Divides one mutable raw slice into two at an index.
    ///
    /// The first will contain all indices from `[0, mid)` (excluding
    /// the index `mid` itself) and the second will contain all
    /// indices from `[mid, len)` (excluding the index `len` itself).
    ///
    /// # Panics
    ///
    /// Panics if `mid > len`.
    ///
    /// # Safety
    ///
    /// `mid` must be [in-bounds] of the underlying [allocated object].
    /// Which means `self` must be dereferenceable and span a single allocation
    /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
    /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
    ///
    /// Since `len` being in-bounds it is not a safety invariant of `*mut [T]` the
    /// safety requirements of this method are the same as for [`split_at_mut_unchecked`].
    /// The explicit bounds check is only as useful as `len` is correct.
    ///
    /// [`split_at_mut_unchecked`]: #method.split_at_mut_unchecked
    /// [in-bounds]: #method.add
    /// [allocated object]: crate::ptr#allocated-object
    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(raw_slice_split)]
    /// #![feature(slice_ptr_get)]
    ///
    /// let mut v = [1, 0, 3, 0, 5, 6];
    /// let ptr = &mut v as *mut [_];
    /// unsafe {
    ///     let (left, right) = ptr.split_at_mut(2);
    ///     assert_eq!(&*left, [1, 0]);
    ///     assert_eq!(&*right, [3, 0, 5, 6]);
    /// }
    /// ```
    #[inline(always)]
    #[track_caller]
    #[unstable(feature = "raw_slice_split", issue = "95595")]
    pub unsafe fn split_at_mut(self, mid: usize) -> (*mut [T], *mut [T]) {
        assert!(mid <= self.len());
        // SAFETY: The assert above is only a safety-net as long as `self.len()` is correct
        // The actual safety requirements of this function are the same as for `split_at_mut_unchecked`
        unsafe { self.split_at_mut_unchecked(mid) }
    }

    /// Divides one mutable raw slice into two at an index, without doing bounds checking.
    ///
    /// The first will contain all indices from `[0, mid)` (excluding
    /// the index `mid` itself) and the second will contain all
    /// indices from `[mid, len)` (excluding the index `len` itself).
    ///
    /// # Safety
    ///
    /// `mid` must be [in-bounds] of the underlying [allocated object].
    /// Which means `self` must be dereferenceable and span a single allocation
    /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
    /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
    ///
    /// [in-bounds]: #method.add
    /// [out-of-bounds index]: #method.add
    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(raw_slice_split)]
    ///
    /// let mut v = [1, 0, 3, 0, 5, 6];
    /// // scoped to restrict the lifetime of the borrows
    /// unsafe {
    ///     let ptr = &mut v as *mut [_];
    ///     let (left, right) = ptr.split_at_mut_unchecked(2);
    ///     assert_eq!(&*left, [1, 0]);
    ///     assert_eq!(&*right, [3, 0, 5, 6]);
    ///     (&mut *left)[1] = 2;
    ///     (&mut *right)[1] = 4;
    /// }
    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
    /// ```
    #[inline(always)]
    #[unstable(feature = "raw_slice_split", issue = "95595")]
    pub unsafe fn split_at_mut_unchecked(self, mid: usize) -> (*mut [T], *mut [T]) {
        let len = self.len();
        let ptr = self.as_mut_ptr();

        // SAFETY: Caller must pass a valid pointer and an index that is in-bounds.
        let tail = unsafe { ptr.add(mid) };
        (
            crate::ptr::slice_from_raw_parts_mut(ptr, mid),
            crate::ptr::slice_from_raw_parts_mut(tail, len - mid),
        )
    }

    /// Returns a raw pointer to the slice's buffer.
    ///
    /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
    ///
    /// # Examples
    ///
    /// ```rust
    /// #![feature(slice_ptr_get)]
    /// use std::ptr;
    ///
    /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
    /// assert_eq!(slice.as_mut_ptr(), ptr::null_mut());
    /// ```
    #[inline(always)]
    #[unstable(feature = "slice_ptr_get", issue = "74265")]
    #[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")]
    pub const fn as_mut_ptr(self) -> *mut T {
        self as *mut T
    }

    /// Returns a raw pointer to an element or subslice, without doing bounds
    /// checking.
    ///
    /// Calling this method with an [out-of-bounds index] or when `self` is not dereferenceable
    /// is *[undefined behavior]* even if the resulting pointer is not used.
    ///
    /// [out-of-bounds index]: #method.add
    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(slice_ptr_get)]
    ///
    /// let x = &mut [1, 2, 4] as *mut [i32];
    ///
    /// unsafe {
    ///     assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
    /// }
    /// ```
    #[unstable(feature = "slice_ptr_get", issue = "74265")]
    #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
    #[inline(always)]
    pub const unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
    where
        I: ~const SliceIndex<[T]>,
    {
        // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds.
        unsafe { index.get_unchecked_mut(self) }
    }

    /// Returns `None` if the pointer is null, or else returns a shared slice to
    /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
    /// that the value has to be initialized.
    ///
    /// For the mutable counterpart see [`as_uninit_slice_mut`].
    ///
    /// [`as_ref`]: #method.as_ref-1
    /// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be [valid] for reads for `ptr.len() * mem::size_of::<T>()` many bytes,
    ///   and it must be properly aligned. This means in particular:
    ///
    ///     * The entire memory range of this slice must be contained within a single [allocated object]!
    ///       Slices can never span across multiple allocated objects.
    ///
    ///     * The pointer must be aligned even for zero-length slices. One
    ///       reason for this is that enum layout optimizations may rely on references
    ///       (including slices of any length) being aligned and non-null to distinguish
    ///       them from other data. You can obtain a pointer that is usable as `data`
    ///       for zero-length slices using [`NonNull::dangling()`].
    ///
    /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get mutated (except inside `UnsafeCell`).
    ///
    /// This applies even if the result of this method is unused!
    ///
    /// See also [`slice::from_raw_parts`][].
    ///
    /// [valid]: crate::ptr#safety
    /// [allocated object]: crate::ptr#allocated-object
    #[inline]
    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
        if self.is_null() {
            None
        } else {
            // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
            Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
        }
    }

    /// Returns `None` if the pointer is null, or else returns a unique slice to
    /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
    /// that the value has to be initialized.
    ///
    /// For the shared counterpart see [`as_uninit_slice`].
    ///
    /// [`as_mut`]: #method.as_mut
    /// [`as_uninit_slice`]: #method.as_uninit_slice-1
    ///
    /// # Safety
    ///
    /// When calling this method, you have to ensure that *either* the pointer is null *or*
    /// all of the following is true:
    ///
    /// * The pointer must be [valid] for reads and writes for `ptr.len() * mem::size_of::<T>()`
    ///   many bytes, and it must be properly aligned. This means in particular:
    ///
    ///     * The entire memory range of this slice must be contained within a single [allocated object]!
    ///       Slices can never span across multiple allocated objects.
    ///
    ///     * The pointer must be aligned even for zero-length slices. One
    ///       reason for this is that enum layout optimizations may rely on references
    ///       (including slices of any length) being aligned and non-null to distinguish
    ///       them from other data. You can obtain a pointer that is usable as `data`
    ///       for zero-length slices using [`NonNull::dangling()`].
    ///
    /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
    ///   In particular, while this reference exists, the memory the pointer points to must
    ///   not get accessed (read or written) through any other pointer.
    ///
    /// This applies even if the result of this method is unused!
    ///
    /// See also [`slice::from_raw_parts_mut`][].
    ///
    /// [valid]: crate::ptr#safety
    /// [allocated object]: crate::ptr#allocated-object
    #[inline]
    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
    pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
        if self.is_null() {
            None
        } else {
            // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
            Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
        }
    }
}

// Equality for pointers
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> PartialEq for *mut T {
    #[inline(always)]
    fn eq(&self, other: &*mut T) -> bool {
        *self == *other
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Eq for *mut T {}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Ord for *mut T {
    #[inline]
    fn cmp(&self, other: &*mut T) -> Ordering {
        if self < other {
            Less
        } else if self == other {
            Equal
        } else {
            Greater
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> PartialOrd for *mut T {
    #[inline(always)]
    fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
        Some(self.cmp(other))
    }

    #[inline(always)]
    fn lt(&self, other: &*mut T) -> bool {
        *self < *other
    }

    #[inline(always)]
    fn le(&self, other: &*mut T) -> bool {
        *self <= *other
    }

    #[inline(always)]
    fn gt(&self, other: &*mut T) -> bool {
        *self > *other
    }

    #[inline(always)]
    fn ge(&self, other: &*mut T) -> bool {
        *self >= *other
    }
}