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rust-lang/portable-simd#250: Add bitmask i{N <8} -> u8 impls

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...and copy the notes for why they're legal.
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Jubilee 2022-03-01 16:10:49 -08:00 committed by GitHub
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8
crates/core_simd/src/intrinsics.rs
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@ -130,6 +130,14 @@ extern "platform-intrinsic" {
pub(crate) fn simd_reduce_xor<T, U>(x: T) -> U;
// truncate integer vector to bitmask
// `fn simd_bitmask(vector) -> unsigned integer` takes a vector of integers and
// returns either an unsigned integer or array of `u8`.
// Every element in the vector becomes a single bit in the returned bitmask.
// If the vector has less than 8 lanes, a u8 is returned with zeroed trailing bits.
// The bit order of the result depends on the byte endianness. LSB-first for little
// endian and MSB-first for big endian.
//
// UB if called on a vector with values other than 0 and -1.
#[allow(unused)]
pub(crate) fn simd_bitmask<T, U>(x: T) -> U;

3
crates/core_simd/src/masks/to_bitmask.rs
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@ -50,6 +50,9 @@ macro_rules! impl_integer_intrinsic {
}
impl_integer_intrinsic! {
unsafe impl ToBitMask<BitMask=u8> for Mask<_, 1>
unsafe impl ToBitMask<BitMask=u8> for Mask<_, 2>
unsafe impl ToBitMask<BitMask=u8> for Mask<_, 4>
unsafe impl ToBitMask<BitMask=u8> for Mask<_, 8>
unsafe impl ToBitMask<BitMask=u16> for Mask<_, 16>
unsafe impl ToBitMask<BitMask=u32> for Mask<_, 32>