core/portable-simd/crates/core_simd/src/vector.rs
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use crate::simd::{
cmp::SimdPartialOrd,
num::SimdUint,
ptr::{SimdConstPtr, SimdMutPtr},
LaneCount, Mask, MaskElement, SupportedLaneCount, Swizzle,
};
/// A SIMD vector with the shape of `[T; N]` but the operations of `T`.
///
/// `Simd<T, N>` supports the operators (+, *, etc.) that `T` does in "elementwise" fashion.
/// These take the element at each index from the left-hand side and right-hand side,
/// perform the operation, then return the result in the same index in a vector of equal size.
/// However, `Simd` differs from normal iteration and normal arrays:
/// - `Simd<T, N>` executes `N` operations in a single step with no `break`s
/// - `Simd<T, N>` can have an alignment greater than `T`, for better mechanical sympathy
///
/// By always imposing these constraints on `Simd`, it is easier to compile elementwise operations
/// into machine instructions that can themselves be executed in parallel.
///
/// ```rust
/// # #![feature(portable_simd)]
/// # use core::simd::{Simd};
/// # use core::array;
/// let a: [i32; 4] = [-2, 0, 2, 4];
/// let b = [10, 9, 8, 7];
/// let sum = array::from_fn(|i| a[i] + b[i]);
/// let prod = array::from_fn(|i| a[i] * b[i]);
///
/// // `Simd<T, N>` implements `From<[T; N]>`
/// let (v, w) = (Simd::from(a), Simd::from(b));
/// // Which means arrays implement `Into<Simd<T, N>>`.
/// assert_eq!(v + w, sum.into());
/// assert_eq!(v * w, prod.into());
/// ```
///
///
/// `Simd` with integer elements treats operators as wrapping, as if `T` was [`Wrapping<T>`].
/// Thus, `Simd` does not implement `wrapping_add`, because that is the default behavior.
/// This means there is no warning on overflows, even in "debug" builds.
/// For most applications where `Simd` is appropriate, it is "not a bug" to wrap,
/// and even "debug builds" are unlikely to tolerate the loss of performance.
/// You may want to consider using explicitly checked arithmetic if such is required.
/// Division by zero on integers still causes a panic, so
/// you may want to consider using `f32` or `f64` if that is unacceptable.
///
/// [`Wrapping<T>`]: core::num::Wrapping
///
/// # Layout
/// `Simd<T, N>` has a layout similar to `[T; N]` (identical "shapes"), with a greater alignment.
/// `[T; N]` is aligned to `T`, but `Simd<T, N>` will have an alignment based on both `T` and `N`.
/// Thus it is sound to [`transmute`] `Simd<T, N>` to `[T; N]` and should optimize to "zero cost",
/// but the reverse transmutation may require a copy the compiler cannot simply elide.
///
/// # ABI "Features"
/// Due to Rust's safety guarantees, `Simd<T, N>` is currently passed and returned via memory,
/// not SIMD registers, except as an optimization. Using `#[inline]` on functions that accept
/// `Simd<T, N>` or return it is recommended, at the cost of code generation time, as
/// inlining SIMD-using functions can omit a large function prolog or epilog and thus
/// improve both speed and code size. The need for this may be corrected in the future.
///
/// Using `#[inline(always)]` still requires additional care.
///
/// # Safe SIMD with Unsafe Rust
///
/// Operations with `Simd` are typically safe, but there are many reasons to want to combine SIMD with `unsafe` code.
/// Care must be taken to respect differences between `Simd` and other types it may be transformed into or derived from.
/// In particular, the layout of `Simd<T, N>` may be similar to `[T; N]`, and may allow some transmutations,
/// but references to `[T; N]` are not interchangeable with those to `Simd<T, N>`.
/// Thus, when using `unsafe` Rust to read and write `Simd<T, N>` through [raw pointers], it is a good idea to first try with
/// [`read_unaligned`] and [`write_unaligned`]. This is because:
/// - [`read`] and [`write`] require full alignment (in this case, `Simd<T, N>`'s alignment)
/// - `Simd<T, N>` is often read from or written to [`[T]`](slice) and other types aligned to `T`
/// - combining these actions violates the `unsafe` contract and explodes the program into
/// a puff of **undefined behavior**
/// - the compiler can implicitly adjust layouts to make unaligned reads or writes fully aligned
/// if it sees the optimization
/// - most contemporary processors with "aligned" and "unaligned" read and write instructions
/// exhibit no performance difference if the "unaligned" variant is aligned at runtime
///
/// Less obligations mean unaligned reads and writes are less likely to make the program unsound,
/// and may be just as fast as stricter alternatives.
/// When trying to guarantee alignment, [`[T]::as_simd`][as_simd] is an option for
/// converting `[T]` to `[Simd<T, N>]`, and allows soundly operating on an aligned SIMD body,
/// but it may cost more time when handling the scalar head and tail.
/// If these are not enough, it is most ideal to design data structures to be already aligned
/// to `mem::align_of::<Simd<T, N>>()` before using `unsafe` Rust to read or write.
/// Other ways to compensate for these facts, like materializing `Simd` to or from an array first,
/// are handled by safe methods like [`Simd::from_array`] and [`Simd::from_slice`].
///
/// [`transmute`]: core::mem::transmute
/// [raw pointers]: pointer
/// [`read_unaligned`]: pointer::read_unaligned
/// [`write_unaligned`]: pointer::write_unaligned
/// [`read`]: pointer::read
/// [`write`]: pointer::write
/// [as_simd]: slice::as_simd
//
// NOTE: Accessing the inner array directly in any way (e.g. by using the `.0` field syntax) or
// directly constructing an instance of the type (i.e. `let vector = Simd(array)`) should be
// avoided, as it will likely become illegal on `#[repr(simd)]` structs in the future. It also
// causes rustc to emit illegal LLVM IR in some cases.
#[repr(simd)]
pub struct Simd<T, const N: usize>([T; N])
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement;
impl<T, const N: usize> Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
/// Number of elements in this vector.
pub const LEN: usize = N;
/// Returns the number of elements in this SIMD vector.
///
/// # Examples
///
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::u32x4;
/// let v = u32x4::splat(0);
/// assert_eq!(v.len(), 4);
/// ```
#[inline]
#[allow(clippy::len_without_is_empty)]
pub const fn len(&self) -> usize {
Self::LEN
}
/// Constructs a new SIMD vector with all elements set to the given value.
///
/// # Examples
///
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::u32x4;
/// let v = u32x4::splat(8);
/// assert_eq!(v.as_array(), &[8, 8, 8, 8]);
/// ```
#[inline]
pub fn splat(value: T) -> Self {
// This is preferred over `[value; N]`, since it's explicitly a splat:
// https://github.com/rust-lang/rust/issues/97804
struct Splat;
impl<const N: usize> Swizzle<N> for Splat {
const INDEX: [usize; N] = [0; N];
}
Splat::swizzle::<T, 1>(Simd::<T, 1>::from([value]))
}
/// Returns an array reference containing the entire SIMD vector.
///
/// # Examples
///
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::{Simd, u64x4};
/// let v: u64x4 = Simd::from_array([0, 1, 2, 3]);
/// assert_eq!(v.as_array(), &[0, 1, 2, 3]);
/// ```
#[inline]
pub const fn as_array(&self) -> &[T; N] {
// SAFETY: `Simd<T, N>` is just an overaligned `[T; N]` with
// potential padding at the end, so pointer casting to a
// `&[T; N]` is safe.
//
// NOTE: This deliberately doesn't just use `&self.0`, see the comment
// on the struct definition for details.
unsafe { &*(self as *const Self as *const [T; N]) }
}
/// Returns a mutable array reference containing the entire SIMD vector.
#[inline]
pub fn as_mut_array(&mut self) -> &mut [T; N] {
// SAFETY: `Simd<T, N>` is just an overaligned `[T; N]` with
// potential padding at the end, so pointer casting to a
// `&mut [T; N]` is safe.
//
// NOTE: This deliberately doesn't just use `&mut self.0`, see the comment
// on the struct definition for details.
unsafe { &mut *(self as *mut Self as *mut [T; N]) }
}
/// Loads a vector from an array of `T`.
///
/// This function is necessary since `repr(simd)` has padding for non-power-of-2 vectors (at the time of writing).
/// With padding, `read_unaligned` will read past the end of an array of N elements.
///
/// # Safety
/// Reading `ptr` must be safe, as if by `<*const [T; N]>::read`.
#[inline]
const unsafe fn load(ptr: *const [T; N]) -> Self {
// There are potentially simpler ways to write this function, but this should result in
// LLVM `load <N x T>`
let mut tmp = core::mem::MaybeUninit::<Self>::uninit();
// SAFETY: `Simd<T, N>` always contains `N` elements of type `T`. It may have padding
// which does not need to be initialized. The safety of reading `ptr` is ensured by the
// caller.
unsafe {
core::ptr::copy_nonoverlapping(ptr, tmp.as_mut_ptr().cast(), 1);
tmp.assume_init()
}
}
/// Store a vector to an array of `T`.
///
/// See `load` as to why this function is necessary.
///
/// # Safety
/// Writing to `ptr` must be safe, as if by `<*mut [T; N]>::write`.
#[inline]
const unsafe fn store(self, ptr: *mut [T; N]) {
// There are potentially simpler ways to write this function, but this should result in
// LLVM `store <N x T>`
// Creating a temporary helps LLVM turn the memcpy into a store.
let tmp = self;
// SAFETY: `Simd<T, N>` always contains `N` elements of type `T`. The safety of writing
// `ptr` is ensured by the caller.
unsafe { core::ptr::copy_nonoverlapping(tmp.as_array(), ptr, 1) }
}
/// Converts an array to a SIMD vector.
#[inline]
pub const fn from_array(array: [T; N]) -> Self {
// SAFETY: `&array` is safe to read.
//
// FIXME: We currently use a pointer load instead of `transmute_copy` because `repr(simd)`
// results in padding for non-power-of-2 vectors (so vectors are larger than arrays).
//
// NOTE: This deliberately doesn't just use `Self(array)`, see the comment
// on the struct definition for details.
unsafe { Self::load(&array) }
}
/// Converts a SIMD vector to an array.
#[inline]
pub const fn to_array(self) -> [T; N] {
let mut tmp = core::mem::MaybeUninit::uninit();
// SAFETY: writing to `tmp` is safe and initializes it.
//
// FIXME: We currently use a pointer store instead of `transmute_copy` because `repr(simd)`
// results in padding for non-power-of-2 vectors (so vectors are larger than arrays).
//
// NOTE: This deliberately doesn't just use `self.0`, see the comment
// on the struct definition for details.
unsafe {
self.store(tmp.as_mut_ptr());
tmp.assume_init()
}
}
/// Converts a slice to a SIMD vector containing `slice[..N]`.
///
/// # Panics
///
/// Panics if the slice's length is less than the vector's `Simd::N`.
/// Use `load_or_default` for an alternative that does not panic.
///
/// # Example
///
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::u32x4;
/// let source = vec![1, 2, 3, 4, 5, 6];
/// let v = u32x4::from_slice(&source);
/// assert_eq!(v.as_array(), &[1, 2, 3, 4]);
/// ```
#[must_use]
#[inline]
#[track_caller]
pub const fn from_slice(slice: &[T]) -> Self {
assert!(
slice.len() >= Self::LEN,
"slice length must be at least the number of elements"
);
// SAFETY: We just checked that the slice contains
// at least `N` elements.
unsafe { Self::load(slice.as_ptr().cast()) }
}
/// Writes a SIMD vector to the first `N` elements of a slice.
///
/// # Panics
///
/// Panics if the slice's length is less than the vector's `Simd::N`.
///
/// # Example
///
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::u32x4;
/// let mut dest = vec![0; 6];
/// let v = u32x4::from_array([1, 2, 3, 4]);
/// v.copy_to_slice(&mut dest);
/// assert_eq!(&dest, &[1, 2, 3, 4, 0, 0]);
/// ```
#[inline]
#[track_caller]
pub fn copy_to_slice(self, slice: &mut [T]) {
assert!(
slice.len() >= Self::LEN,
"slice length must be at least the number of elements"
);
// SAFETY: We just checked that the slice contains
// at least `N` elements.
unsafe { self.store(slice.as_mut_ptr().cast()) }
}
/// Reads contiguous elements from `slice`. Elements are read so long as they're in-bounds for
/// the `slice`. Otherwise, the default value for the element type is returned.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::Simd;
/// let vec: Vec<i32> = vec![10, 11];
///
/// let result = Simd::<i32, 4>::load_or_default(&vec);
/// assert_eq!(result, Simd::from_array([10, 11, 0, 0]));
/// ```
#[must_use]
#[inline]
pub fn load_or_default(slice: &[T]) -> Self
where
T: Default,
{
Self::load_or(slice, Default::default())
}
/// Reads contiguous elements from `slice`. Elements are read so long as they're in-bounds for
/// the `slice`. Otherwise, the corresponding value from `or` is passed through.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::Simd;
/// let vec: Vec<i32> = vec![10, 11];
/// let or = Simd::from_array([-5, -4, -3, -2]);
///
/// let result = Simd::load_or(&vec, or);
/// assert_eq!(result, Simd::from_array([10, 11, -3, -2]));
/// ```
#[must_use]
#[inline]
pub fn load_or(slice: &[T], or: Self) -> Self {
Self::load_select(slice, Mask::splat(true), or)
}
/// Reads contiguous elements from `slice`. Each element is read from memory if its
/// corresponding element in `enable` is `true`.
///
/// When the element is disabled or out of bounds for the slice, that memory location
/// is not accessed and the corresponding value from `or` is passed through.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, Mask};
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let enable = Mask::from_array([true, true, false, true]);
/// let or = Simd::from_array([-5, -4, -3, -2]);
///
/// let result = Simd::load_select(&vec, enable, or);
/// assert_eq!(result, Simd::from_array([10, 11, -3, 13]));
/// ```
#[must_use]
#[inline]
pub fn load_select_or_default(slice: &[T], enable: Mask<<T as SimdElement>::Mask, N>) -> Self
where
T: Default,
{
Self::load_select(slice, enable, Default::default())
}
/// Reads contiguous elements from `slice`. Each element is read from memory if its
/// corresponding element in `enable` is `true`.
///
/// When the element is disabled or out of bounds for the slice, that memory location
/// is not accessed and the corresponding value from `or` is passed through.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, Mask};
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let enable = Mask::from_array([true, true, false, true]);
/// let or = Simd::from_array([-5, -4, -3, -2]);
///
/// let result = Simd::load_select(&vec, enable, or);
/// assert_eq!(result, Simd::from_array([10, 11, -3, 13]));
/// ```
#[must_use]
#[inline]
pub fn load_select(
slice: &[T],
mut enable: Mask<<T as SimdElement>::Mask, N>,
or: Self,
) -> Self {
enable &= mask_up_to(slice.len());
// SAFETY: We performed the bounds check by updating the mask. &[T] is properly aligned to
// the element.
unsafe { Self::load_select_ptr(slice.as_ptr(), enable, or) }
}
/// Reads contiguous elements from `slice`. Each element is read from memory if its
/// corresponding element in `enable` is `true`.
///
/// When the element is disabled, that memory location is not accessed and the corresponding
/// value from `or` is passed through.
#[must_use]
#[inline]
pub unsafe fn load_select_unchecked(
slice: &[T],
enable: Mask<<T as SimdElement>::Mask, N>,
or: Self,
) -> Self {
let ptr = slice.as_ptr();
// SAFETY: The safety of reading elements from `slice` is ensured by the caller.
unsafe { Self::load_select_ptr(ptr, enable, or) }
}
/// Reads contiguous elements starting at `ptr`. Each element is read from memory if its
/// corresponding element in `enable` is `true`.
///
/// When the element is disabled, that memory location is not accessed and the corresponding
/// value from `or` is passed through.
#[must_use]
#[inline]
pub unsafe fn load_select_ptr(
ptr: *const T,
enable: Mask<<T as SimdElement>::Mask, N>,
or: Self,
) -> Self {
// SAFETY: The safety of reading elements through `ptr` is ensured by the caller.
unsafe { core::intrinsics::simd::simd_masked_load(enable.to_int(), ptr, or) }
}
/// Reads from potentially discontiguous indices in `slice` to construct a SIMD vector.
/// If an index is out-of-bounds, the element is instead selected from the `or` vector.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::Simd;
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 5]); // Note the index that is out-of-bounds
/// let alt = Simd::from_array([-5, -4, -3, -2]);
///
/// let result = Simd::gather_or(&vec, idxs, alt);
/// assert_eq!(result, Simd::from_array([-5, 13, 10, 15]));
/// ```
#[must_use]
#[inline]
pub fn gather_or(slice: &[T], idxs: Simd<usize, N>, or: Self) -> Self {
Self::gather_select(slice, Mask::splat(true), idxs, or)
}
/// Reads from indices in `slice` to construct a SIMD vector.
/// If an index is out-of-bounds, the element is set to the default given by `T: Default`.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::Simd;
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 5]); // Note the index that is out-of-bounds
///
/// let result = Simd::gather_or_default(&vec, idxs);
/// assert_eq!(result, Simd::from_array([0, 13, 10, 15]));
/// ```
#[must_use]
#[inline]
pub fn gather_or_default(slice: &[T], idxs: Simd<usize, N>) -> Self
where
T: Default,
{
Self::gather_or(slice, idxs, Self::splat(T::default()))
}
/// Reads from indices in `slice` to construct a SIMD vector.
/// The mask `enable`s all `true` indices and disables all `false` indices.
/// If an index is disabled or is out-of-bounds, the element is selected from the `or` vector.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::{Simd, Mask};
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 5]); // Includes an out-of-bounds index
/// let alt = Simd::from_array([-5, -4, -3, -2]);
/// let enable = Mask::from_array([true, true, true, false]); // Includes a masked element
///
/// let result = Simd::gather_select(&vec, enable, idxs, alt);
/// assert_eq!(result, Simd::from_array([-5, 13, 10, -2]));
/// ```
#[must_use]
#[inline]
pub fn gather_select(
slice: &[T],
enable: Mask<isize, N>,
idxs: Simd<usize, N>,
or: Self,
) -> Self {
let enable: Mask<isize, N> = enable & idxs.simd_lt(Simd::splat(slice.len()));
// Safety: We have masked-off out-of-bounds indices.
unsafe { Self::gather_select_unchecked(slice, enable, idxs, or) }
}
/// Reads from indices in `slice` to construct a SIMD vector.
/// The mask `enable`s all `true` indices and disables all `false` indices.
/// If an index is disabled, the element is selected from the `or` vector.
///
/// # Safety
///
/// Calling this function with an `enable`d out-of-bounds index is *[undefined behavior]*
/// even if the resulting value is not used.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, cmp::SimdPartialOrd, Mask};
/// let vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 5]); // Includes an out-of-bounds index
/// let alt = Simd::from_array([-5, -4, -3, -2]);
/// let enable = Mask::from_array([true, true, true, false]); // Includes a masked element
/// // If this mask was used to gather, it would be unsound. Let's fix that.
/// let enable = enable & idxs.simd_lt(Simd::splat(vec.len()));
///
/// // The out-of-bounds index has been masked, so it's safe to gather now.
/// let result = unsafe { Simd::gather_select_unchecked(&vec, enable, idxs, alt) };
/// assert_eq!(result, Simd::from_array([-5, 13, 10, -2]));
/// ```
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[must_use]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn gather_select_unchecked(
slice: &[T],
enable: Mask<isize, N>,
idxs: Simd<usize, N>,
or: Self,
) -> Self {
let base_ptr = Simd::<*const T, N>::splat(slice.as_ptr());
// Ferris forgive me, I have done pointer arithmetic here.
let ptrs = base_ptr.wrapping_add(idxs);
// Safety: The caller is responsible for determining the indices are okay to read
unsafe { Self::gather_select_ptr(ptrs, enable, or) }
}
/// Reads elementwise from pointers into a SIMD vector.
///
/// # Safety
///
/// Each read must satisfy the same conditions as [`core::ptr::read`].
///
/// # Example
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::prelude::*;
/// let values = [6, 2, 4, 9];
/// let offsets = Simd::from_array([1, 0, 0, 3]);
/// let source = Simd::splat(values.as_ptr()).wrapping_add(offsets);
/// let gathered = unsafe { Simd::gather_ptr(source) };
/// assert_eq!(gathered, Simd::from_array([2, 6, 6, 9]));
/// ```
#[must_use]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn gather_ptr(source: Simd<*const T, N>) -> Self
where
T: Default,
{
// TODO: add an intrinsic that doesn't use a passthru vector, and remove the T: Default bound
// Safety: The caller is responsible for upholding all invariants
unsafe { Self::gather_select_ptr(source, Mask::splat(true), Self::default()) }
}
/// Conditionally read elementwise from pointers into a SIMD vector.
/// The mask `enable`s all `true` pointers and disables all `false` pointers.
/// If a pointer is disabled, the element is selected from the `or` vector,
/// and no read is performed.
///
/// # Safety
///
/// Enabled elements must satisfy the same conditions as [`core::ptr::read`].
///
/// # Example
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::prelude::*;
/// let values = [6, 2, 4, 9];
/// let enable = Mask::from_array([true, true, false, true]);
/// let offsets = Simd::from_array([1, 0, 0, 3]);
/// let source = Simd::splat(values.as_ptr()).wrapping_add(offsets);
/// let gathered = unsafe { Simd::gather_select_ptr(source, enable, Simd::splat(0)) };
/// assert_eq!(gathered, Simd::from_array([2, 6, 0, 9]));
/// ```
#[must_use]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn gather_select_ptr(
source: Simd<*const T, N>,
enable: Mask<isize, N>,
or: Self,
) -> Self {
// Safety: The caller is responsible for upholding all invariants
unsafe { core::intrinsics::simd::simd_gather(or, source, enable.to_int()) }
}
/// Conditionally write contiguous elements to `slice`. The `enable` mask controls
/// which elements are written, as long as they're in-bounds of the `slice`.
/// If the element is disabled or out of bounds, no memory access to that location
/// is made.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, Mask};
/// let mut arr = [0i32; 4];
/// let write = Simd::from_array([-5, -4, -3, -2]);
/// let enable = Mask::from_array([false, true, true, true]);
///
/// write.store_select(&mut arr[..3], enable);
/// assert_eq!(arr, [0, -4, -3, 0]);
/// ```
#[inline]
pub fn store_select(self, slice: &mut [T], mut enable: Mask<<T as SimdElement>::Mask, N>) {
enable &= mask_up_to(slice.len());
// SAFETY: We performed the bounds check by updating the mask. &[T] is properly aligned to
// the element.
unsafe { self.store_select_ptr(slice.as_mut_ptr(), enable) }
}
/// Conditionally write contiguous elements to `slice`. The `enable` mask controls
/// which elements are written.
///
/// # Safety
///
/// Every enabled element must be in bounds for the `slice`.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, Mask};
/// let mut arr = [0i32; 4];
/// let write = Simd::from_array([-5, -4, -3, -2]);
/// let enable = Mask::from_array([false, true, true, true]);
///
/// unsafe { write.store_select_unchecked(&mut arr, enable) };
/// assert_eq!(arr, [0, -4, -3, -2]);
/// ```
#[inline]
pub unsafe fn store_select_unchecked(
self,
slice: &mut [T],
enable: Mask<<T as SimdElement>::Mask, N>,
) {
let ptr = slice.as_mut_ptr();
// SAFETY: The safety of writing elements in `slice` is ensured by the caller.
unsafe { self.store_select_ptr(ptr, enable) }
}
/// Conditionally write contiguous elements starting from `ptr`.
/// The `enable` mask controls which elements are written.
/// When disabled, the memory location corresponding to that element is not accessed.
///
/// # Safety
///
/// Memory addresses for element are calculated [`pointer::wrapping_offset`] and
/// each enabled element must satisfy the same conditions as [`core::ptr::write`].
#[inline]
pub unsafe fn store_select_ptr(self, ptr: *mut T, enable: Mask<<T as SimdElement>::Mask, N>) {
// SAFETY: The safety of writing elements through `ptr` is ensured by the caller.
unsafe { core::intrinsics::simd::simd_masked_store(enable.to_int(), ptr, self) }
}
/// Writes the values in a SIMD vector to potentially discontiguous indices in `slice`.
/// If an index is out-of-bounds, the write is suppressed without panicking.
/// If two elements in the scattered vector would write to the same index
/// only the last element is guaranteed to actually be written.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # use core::simd::Simd;
/// let mut vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 0]); // Note the duplicate index.
/// let vals = Simd::from_array([-27, 82, -41, 124]);
///
/// vals.scatter(&mut vec, idxs); // two logical writes means the last wins.
/// assert_eq!(vec, vec![124, 11, 12, 82, 14, 15, 16, 17, 18]);
/// ```
#[inline]
pub fn scatter(self, slice: &mut [T], idxs: Simd<usize, N>) {
self.scatter_select(slice, Mask::splat(true), idxs)
}
/// Writes values from a SIMD vector to multiple potentially discontiguous indices in `slice`.
/// The mask `enable`s all `true` indices and disables all `false` indices.
/// If an enabled index is out-of-bounds, the write is suppressed without panicking.
/// If two enabled elements in the scattered vector would write to the same index,
/// only the last element is guaranteed to actually be written.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, Mask};
/// let mut vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 0]); // Includes an out-of-bounds index
/// let vals = Simd::from_array([-27, 82, -41, 124]);
/// let enable = Mask::from_array([true, true, true, false]); // Includes a masked element
///
/// vals.scatter_select(&mut vec, enable, idxs); // The last write is masked, thus omitted.
/// assert_eq!(vec, vec![-41, 11, 12, 82, 14, 15, 16, 17, 18]);
/// ```
#[inline]
pub fn scatter_select(self, slice: &mut [T], enable: Mask<isize, N>, idxs: Simd<usize, N>) {
let enable: Mask<isize, N> = enable & idxs.simd_lt(Simd::splat(slice.len()));
// Safety: We have masked-off out-of-bounds indices.
unsafe { self.scatter_select_unchecked(slice, enable, idxs) }
}
/// Writes values from a SIMD vector to multiple potentially discontiguous indices in `slice`.
/// The mask `enable`s all `true` indices and disables all `false` indices.
/// If two enabled elements in the scattered vector would write to the same index,
/// only the last element is guaranteed to actually be written.
///
/// # Safety
///
/// Calling this function with an enabled out-of-bounds index is *[undefined behavior]*,
/// and may lead to memory corruption.
///
/// # Examples
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, cmp::SimdPartialOrd, Mask};
/// let mut vec: Vec<i32> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
/// let idxs = Simd::from_array([9, 3, 0, 0]);
/// let vals = Simd::from_array([-27, 82, -41, 124]);
/// let enable = Mask::from_array([true, true, true, false]); // Masks the final index
/// // If this mask was used to scatter, it would be unsound. Let's fix that.
/// let enable = enable & idxs.simd_lt(Simd::splat(vec.len()));
///
/// // We have masked the OOB index, so it's safe to scatter now.
/// unsafe { vals.scatter_select_unchecked(&mut vec, enable, idxs); }
/// // The second write to index 0 was masked, thus omitted.
/// assert_eq!(vec, vec![-41, 11, 12, 82, 14, 15, 16, 17, 18]);
/// ```
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn scatter_select_unchecked(
self,
slice: &mut [T],
enable: Mask<isize, N>,
idxs: Simd<usize, N>,
) {
// Safety: This block works with *mut T derived from &mut 'a [T],
// which means it is delicate in Rust's borrowing model, circa 2021:
// &mut 'a [T] asserts uniqueness, so deriving &'a [T] invalidates live *mut Ts!
// Even though this block is largely safe methods, it must be exactly this way
// to prevent invalidating the raw ptrs while they're live.
// Thus, entering this block requires all values to use being already ready:
// 0. idxs we want to write to, which are used to construct the mask.
// 1. enable, which depends on an initial &'a [T] and the idxs.
// 2. actual values to scatter (self).
// 3. &mut [T] which will become our base ptr.
unsafe {
// Now Entering ☢️ *mut T Zone
let base_ptr = Simd::<*mut T, N>::splat(slice.as_mut_ptr());
// Ferris forgive me, I have done pointer arithmetic here.
let ptrs = base_ptr.wrapping_add(idxs);
// The ptrs have been bounds-masked to prevent memory-unsafe writes insha'allah
self.scatter_select_ptr(ptrs, enable);
// Cleared ☢️ *mut T Zone
}
}
/// Writes pointers elementwise into a SIMD vector.
///
/// # Safety
///
/// Each write must satisfy the same conditions as [`core::ptr::write`].
///
/// # Example
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Simd, ptr::SimdMutPtr};
/// let mut values = [0; 4];
/// let offset = Simd::from_array([3, 2, 1, 0]);
/// let ptrs = Simd::splat(values.as_mut_ptr()).wrapping_add(offset);
/// unsafe { Simd::from_array([6, 3, 5, 7]).scatter_ptr(ptrs); }
/// assert_eq!(values, [7, 5, 3, 6]);
/// ```
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn scatter_ptr(self, dest: Simd<*mut T, N>) {
// Safety: The caller is responsible for upholding all invariants
unsafe { self.scatter_select_ptr(dest, Mask::splat(true)) }
}
/// Conditionally write pointers elementwise into a SIMD vector.
/// The mask `enable`s all `true` pointers and disables all `false` pointers.
/// If a pointer is disabled, the write to its pointee is skipped.
///
/// # Safety
///
/// Enabled pointers must satisfy the same conditions as [`core::ptr::write`].
///
/// # Example
/// ```
/// # #![feature(portable_simd)]
/// # #[cfg(feature = "as_crate")] use core_simd::simd;
/// # #[cfg(not(feature = "as_crate"))] use core::simd;
/// # use simd::{Mask, Simd, ptr::SimdMutPtr};
/// let mut values = [0; 4];
/// let offset = Simd::from_array([3, 2, 1, 0]);
/// let ptrs = Simd::splat(values.as_mut_ptr()).wrapping_add(offset);
/// let enable = Mask::from_array([true, true, false, false]);
/// unsafe { Simd::from_array([6, 3, 5, 7]).scatter_select_ptr(ptrs, enable); }
/// assert_eq!(values, [0, 0, 3, 6]);
/// ```
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub unsafe fn scatter_select_ptr(self, dest: Simd<*mut T, N>, enable: Mask<isize, N>) {
// Safety: The caller is responsible for upholding all invariants
unsafe { core::intrinsics::simd::simd_scatter(self, dest, enable.to_int()) }
}
}
impl<T, const N: usize> Copy for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
}
impl<T, const N: usize> Clone for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn clone(&self) -> Self {
*self
}
}
impl<T, const N: usize> Default for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + Default,
{
#[inline]
fn default() -> Self {
Self::splat(T::default())
}
}
impl<T, const N: usize> PartialEq for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + PartialEq,
{
#[inline]
fn eq(&self, other: &Self) -> bool {
// Safety: All SIMD vectors are SimdPartialEq, and the comparison produces a valid mask.
let mask = unsafe {
let tfvec: Simd<<T as SimdElement>::Mask, N> =
core::intrinsics::simd::simd_eq(*self, *other);
Mask::from_int_unchecked(tfvec)
};
// Two vectors are equal if all elements are equal when compared elementwise
mask.all()
}
#[allow(clippy::partialeq_ne_impl)]
#[inline]
fn ne(&self, other: &Self) -> bool {
// Safety: All SIMD vectors are SimdPartialEq, and the comparison produces a valid mask.
let mask = unsafe {
let tfvec: Simd<<T as SimdElement>::Mask, N> =
core::intrinsics::simd::simd_ne(*self, *other);
Mask::from_int_unchecked(tfvec)
};
// Two vectors are non-equal if any elements are non-equal when compared elementwise
mask.any()
}
}
impl<T, const N: usize> PartialOrd for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + PartialOrd,
{
#[inline]
fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
// TODO use SIMD equality
self.to_array().partial_cmp(other.as_ref())
}
}
impl<T, const N: usize> Eq for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + Eq,
{
}
impl<T, const N: usize> Ord for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + Ord,
{
#[inline]
fn cmp(&self, other: &Self) -> core::cmp::Ordering {
// TODO use SIMD equality
self.to_array().cmp(other.as_ref())
}
}
impl<T, const N: usize> core::hash::Hash for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + core::hash::Hash,
{
#[inline]
fn hash<H>(&self, state: &mut H)
where
H: core::hash::Hasher,
{
self.as_array().hash(state)
}
}
// array references
impl<T, const N: usize> AsRef<[T; N]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn as_ref(&self) -> &[T; N] {
self.as_array()
}
}
impl<T, const N: usize> AsMut<[T; N]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn as_mut(&mut self) -> &mut [T; N] {
self.as_mut_array()
}
}
// slice references
impl<T, const N: usize> AsRef<[T]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn as_ref(&self) -> &[T] {
self.as_array()
}
}
impl<T, const N: usize> AsMut<[T]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn as_mut(&mut self) -> &mut [T] {
self.as_mut_array()
}
}
// vector/array conversion
impl<T, const N: usize> From<[T; N]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn from(array: [T; N]) -> Self {
Self::from_array(array)
}
}
impl<T, const N: usize> From<Simd<T, N>> for [T; N]
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
#[inline]
fn from(vector: Simd<T, N>) -> Self {
vector.to_array()
}
}
impl<T, const N: usize> TryFrom<&[T]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
type Error = core::array::TryFromSliceError;
#[inline]
fn try_from(slice: &[T]) -> Result<Self, core::array::TryFromSliceError> {
Ok(Self::from_array(slice.try_into()?))
}
}
impl<T, const N: usize> TryFrom<&mut [T]> for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement,
{
type Error = core::array::TryFromSliceError;
#[inline]
fn try_from(slice: &mut [T]) -> Result<Self, core::array::TryFromSliceError> {
Ok(Self::from_array(slice.try_into()?))
}
}
mod sealed {
pub trait Sealed {}
}
use sealed::Sealed;
/// Marker trait for types that may be used as SIMD vector elements.
///
/// # Safety
/// This trait, when implemented, asserts the compiler can monomorphize
/// `#[repr(simd)]` structs with the marked type as an element.
/// Strictly, it is valid to impl if the vector will not be miscompiled.
/// Practically, it is user-unfriendly to impl it if the vector won't compile,
/// even when no soundness guarantees are broken by allowing the user to try.
pub unsafe trait SimdElement: Sealed + Copy {
/// The mask element type corresponding to this element type.
type Mask: MaskElement;
}
impl Sealed for u8 {}
// Safety: u8 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for u8 {
type Mask = i8;
}
impl Sealed for u16 {}
// Safety: u16 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for u16 {
type Mask = i16;
}
impl Sealed for u32 {}
// Safety: u32 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for u32 {
type Mask = i32;
}
impl Sealed for u64 {}
// Safety: u64 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for u64 {
type Mask = i64;
}
impl Sealed for usize {}
// Safety: usize is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for usize {
type Mask = isize;
}
impl Sealed for i8 {}
// Safety: i8 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for i8 {
type Mask = i8;
}
impl Sealed for i16 {}
// Safety: i16 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for i16 {
type Mask = i16;
}
impl Sealed for i32 {}
// Safety: i32 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for i32 {
type Mask = i32;
}
impl Sealed for i64 {}
// Safety: i64 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for i64 {
type Mask = i64;
}
impl Sealed for isize {}
// Safety: isize is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for isize {
type Mask = isize;
}
impl Sealed for f32 {}
// Safety: f32 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for f32 {
type Mask = i32;
}
impl Sealed for f64 {}
// Safety: f64 is a valid SIMD element type, and is supported by this API
unsafe impl SimdElement for f64 {
type Mask = i64;
}
impl<T> Sealed for *const T {}
// Safety: (thin) const pointers are valid SIMD element types, and are supported by this API
//
// Fat pointers may be supported in the future.
unsafe impl<T> SimdElement for *const T
where
T: core::ptr::Pointee<Metadata = ()>,
{
type Mask = isize;
}
impl<T> Sealed for *mut T {}
// Safety: (thin) mut pointers are valid SIMD element types, and are supported by this API
//
// Fat pointers may be supported in the future.
unsafe impl<T> SimdElement for *mut T
where
T: core::ptr::Pointee<Metadata = ()>,
{
type Mask = isize;
}
#[inline]
fn lane_indices<const N: usize>() -> Simd<usize, N>
where
LaneCount<N>: SupportedLaneCount,
{
let mut index = [0; N];
for i in 0..N {
index[i] = i;
}
Simd::from_array(index)
}
#[inline]
fn mask_up_to<M, const N: usize>(len: usize) -> Mask<M, N>
where
LaneCount<N>: SupportedLaneCount,
M: MaskElement,
{
let index = lane_indices::<N>();
let max_value: u64 = M::max_unsigned();
macro_rules! case {
($ty:ty) => {
if N < <$ty>::MAX as usize && max_value as $ty as u64 == max_value {
return index.cast().simd_lt(Simd::splat(len.min(N) as $ty)).cast();
}
};
}
case!(u8);
case!(u16);
case!(u32);
case!(u64);
index.simd_lt(Simd::splat(len)).cast()
}