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Improve simd_bitmask documentation and other minor fixes

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This commit is contained in:
Caleb Zulawski 2023-12-17 13:01:52 -05:00
parent 560ac23b70
commit 71a5698989
1 changed files with 15 additions and 8 deletions
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23
library/core/src/intrinsics/simd.rs
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@ -199,6 +199,8 @@ extern "platform-intrinsic" {
/// ///
/// `V` must be a vector of integers with the same length as `T` (but any element size). /// `V` must be a vector of integers with the same length as `T` (but any element size).
/// ///
/// `idx` must be a constant.
///
/// For each pointer in `ptr`, if the corresponding value in `mask` is `!0`, read the pointer. /// For each pointer in `ptr`, if the corresponding value in `mask` is `!0`, read the pointer.
/// Otherwise if the corresponding value in `mask` is `0`, return the corresponding value from /// Otherwise if the corresponding value in `mask` is `0`, return the corresponding value from
/// `val`. /// `val`.
@ -319,15 +321,20 @@ extern "platform-intrinsic" {
/// `T` must be an integer vector. /// `T` must be an integer vector.
/// ///
/// `U` must be either the smallest unsigned integer with at least as many bits as the length /// `U` must be either the smallest unsigned integer with at least as many bits as the length
/// of `T`, or the smallest array of `u8` with as many bits as the length of `T`.
/// ///
/// Each element is truncated to a single bit and packed into the result. /// Each element is truncated to a single bit and packed into the result.
/// ///
/// The bit order depends on the byte endianness. /// No matter whether the output is an array or an unsigned integer, it is treated as a single
/// The bitmask is always packed into the smallest/first bits, but the order is LSB-first for /// contiguous list of bits. The bitmask is always packed on the least-significant side of the
/// little endian and MSB-first for big endian. /// output, and padded with 0s in the most-significant bits. The order of the bits depends on
/// In other words, the LSB corresponds to the first vector element for little endian, /// endianess:
/// and the last vector element for big endian. ///
/// of `T`, or the smallest array of `u8` with as many bits as the length of `T`. /// * On little endian, the least significant bit corresponds to the first vector element.
/// * On big endian, the least significant bit corresponds to the last vector element.
///
/// For example, `[-1, 0, -1, -1]` packs to `0b1101` on little endian and `0b1011` on big
/// endian.
/// ///
/// # Safety /// # Safety
/// `x` must contain only `0` and `!0`. /// `x` must contain only `0` and `!0`.
@ -349,7 +356,7 @@ extern "platform-intrinsic" {
/// Select elements from a bitmask. /// Select elements from a bitmask.
/// ///
/// `M` must be an unsigned integer of type matching `simd_bitmask`. /// `M` must be an unsigned integer or array of `u8`, matching `simd_bitmask`.
/// ///
/// `T` must be a vector. /// `T` must be a vector.
/// ///
@ -360,7 +367,7 @@ extern "platform-intrinsic" {
/// The bitmask bit order matches `simd_bitmask`. /// The bitmask bit order matches `simd_bitmask`.
/// ///
/// # Safety /// # Safety
/// `mask` must only contain `0` and `!0`. /// Padding bits must be all zero.
pub fn simd_select_bitmask<M, T>(m: M, yes: T, no: T) -> T; pub fn simd_select_bitmask<M, T>(m: M, yes: T, no: T) -> T;
/// Elementwise calculates the offset from a pointer vector, potentially wrapping. /// Elementwise calculates the offset from a pointer vector, potentially wrapping.