core/num/dec2flt/
common.rs

Help
1//! Common utilities, for internal use only.
2
3/// Helper methods to process immutable bytes.
4pub(crate) trait ByteSlice {
5    /// Reads 8 bytes as a 64-bit integer in little-endian order.
6    fn read_u64(&self) -> u64;
7
8    /// Writes a 64-bit integer as 8 bytes in little-endian order.
9    fn write_u64(&mut self, value: u64);
10
11    /// Calculate the offset of a slice from another.
12    fn offset_from(&self, other: &Self) -> isize;
13
14    /// Iteratively parse and consume digits from bytes.
15    /// Returns the same bytes with consumed digits being
16    /// elided.
17    fn parse_digits(&self, func: impl FnMut(u8)) -> &Self;
18}
19
20impl ByteSlice for [u8] {
21    #[inline(always)] // inlining this is crucial to remove bound checks
22    fn read_u64(&self) -> u64 {
23        let mut tmp = [0; 8];
24        tmp.copy_from_slice(&self[..8]);
25        u64::from_le_bytes(tmp)
26    }
27
28    #[inline(always)] // inlining this is crucial to remove bound checks
29    fn write_u64(&mut self, value: u64) {
30        self[..8].copy_from_slice(&value.to_le_bytes())
31    }
32
33    #[inline]
34    fn offset_from(&self, other: &Self) -> isize {
35        other.len() as isize - self.len() as isize
36    }
37
38    #[inline]
39    fn parse_digits(&self, mut func: impl FnMut(u8)) -> &Self {
40        let mut s = self;
41
42        while let Some((c, s_next)) = s.split_first() {
43            let c = c.wrapping_sub(b'0');
44            if c < 10 {
45                func(c);
46                s = s_next;
47            } else {
48                break;
49            }
50        }
51
52        s
53    }
54}
55
56/// Determine if 8 bytes are all decimal digits.
57/// This does not care about the order in which the bytes were loaded.
58pub(crate) fn is_8digits(v: u64) -> bool {
59    let a = v.wrapping_add(0x4646_4646_4646_4646);
60    let b = v.wrapping_sub(0x3030_3030_3030_3030);
61    (a | b) & 0x8080_8080_8080_8080 == 0
62}
63
64/// A custom 64-bit floating point type, representing `f * 2^e`.
65/// e is biased, so it be directly shifted into the exponent bits.
66#[derive(Debug, Copy, Clone, PartialEq, Eq, Default)]
67pub struct BiasedFp {
68    /// The significant digits.
69    pub f: u64,
70    /// The biased, binary exponent.
71    pub e: i32,
72}
73
74impl BiasedFp {
75    #[inline]
76    pub const fn zero_pow2(e: i32) -> Self {
77        Self { f: 0, e }
78    }
79}
core/num/dec2flt/common.rs

core/num/dec2flt/
common.rs
