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perf(parser): use - not saturating_sub (#4561)

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Follow-on after #4304. Avoid using `saturating_sub` when plain `-` will do. `-` is cheaper - it's a single assembly instruction, whereas `saturating_sub` is usually 3 instructions.

https://godbolt.org/z/fo8Tcx6bK
This commit is contained in:
overlookmotel 2024-07-31 00:28:46 +00:00
parent 7585e16beb
commit ab8509edaa
1 changed files with 4 additions and 2 deletions
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6
crates/oxc_parser/src/lexer/source.rs
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@ -501,9 +501,11 @@ impl<'a> Source<'a> {
/// Peek next two bytes of source without consuming them.
#[inline]
pub(super) fn peek_2_bytes(&self) -> Option<[u8; 2]> {
if (self.end as usize).saturating_sub(self.ptr as usize) >= 2 {
// `end` is always >= `ptr` so `end - ptr` cannot wrap around.
// No need to use checked/saturating subtraction here.
if (self.end as usize) - (self.ptr as usize) >= 2 {
// SAFETY: The check above ensures that there are at least 2 bytes to
// read from `self.ptr` without overflowing past `self.end`.
// read from `self.ptr` without reading past `self.end`
let bytes = unsafe { self.position().read2() };
Some(bytes)
} else {