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Auto merge of #118315 - WaffleLapkin:don't-repeat_byte, r=m-ou-se

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Use `usize::repeat_u8` instead of implementing `repeat_byte` in `memchr.rs`

It's simpler that way and the tricks don't actually make a difference: https://godbolt.org/z/zrvYY1dGx
This commit is contained in:
bors 2023-11-29 13:39:19 +00:00
commit abe34e9ab1
1 changed files with 2 additions and 16 deletions
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18
library/core/src/slice/memchr.rs
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@ -20,20 +20,6 @@ const fn contains_zero_byte(x: usize) -> bool {
x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0 x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
} }
#[inline]
#[cfg(target_pointer_width = "16")]
#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
const fn repeat_byte(b: u8) -> usize {
(b as usize) << 8 | b as usize
}
#[inline]
#[cfg(not(target_pointer_width = "16"))]
#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
const fn repeat_byte(b: u8) -> usize {
(b as usize) * (usize::MAX / 255)
}
/// Returns the first index matching the byte `x` in `text`. /// Returns the first index matching the byte `x` in `text`.
#[inline] #[inline]
#[must_use] #[must_use]
@ -93,7 +79,7 @@ const fn memchr_aligned(x: u8, text: &[u8]) -> Option<usize> {
} }
// search the body of the text // search the body of the text
let repeated_x = repeat_byte(x); let repeated_x = usize::repeat_u8(x);
while offset <= len - 2 * USIZE_BYTES { while offset <= len - 2 * USIZE_BYTES {
// SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes // SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes
// between the offset and the end of the slice. // between the offset and the end of the slice.
@ -149,7 +135,7 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
// Search the body of the text, make sure we don't cross min_aligned_offset. // Search the body of the text, make sure we don't cross min_aligned_offset.
// offset is always aligned, so just testing `>` is sufficient and avoids possible // offset is always aligned, so just testing `>` is sufficient and avoids possible
// overflow. // overflow.
let repeated_x = repeat_byte(x); let repeated_x = usize::repeat_u8(x);
let chunk_bytes = mem::size_of::<Chunk>(); let chunk_bytes = mem::size_of::<Chunk>();
while offset > min_aligned_offset { while offset > min_aligned_offset {