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Use usize::repeat_u8 instead of implementing repeat_byte in memchr.rs #118315

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Merged
merged 1 commit into from
Nov 29, 2023
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Use usize::repeat_u8 instead of implementing repeat_byte in memchr.rs #118315

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18 changes: 2 additions & 16 deletions library/core/src/slice/memchr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,20 +20,6 @@ const fn contains_zero_byte(x: usize) -> bool {
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`.
#[inline]
#[must_use]
Expand Down Expand Up @@ -93,7 +79,7 @@ const fn memchr_aligned(x: u8, text: &[u8]) -> Option<usize> {
}

// 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 {
// SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes
// between the offset and the end of the slice.
Expand Down Expand Up @@ -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.
// offset is always aligned, so just testing `>` is sufficient and avoids possible
// overflow.
let repeated_x = repeat_byte(x);
let repeated_x = usize::repeat_u8(x);
let chunk_bytes = mem::size_of::<Chunk>();

while offset > min_aligned_offset {
Expand Down