Rollup merge of #32456 - bluss:str-zero, r=alexcrichton
Hardcode accepting 0 as a valid str char boundary If we check explicitly for index == 0, that removes the need to read the byte at index 0, so it avoids a trip to the string's memory, and it optimizes out the slicing index' bounds check whenever it is (a constant) zero.
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671027817c
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@ -1953,7 +1953,10 @@ impl StrExt for str {
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#[inline]
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#[inline]
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fn is_char_boundary(&self, index: usize) -> bool {
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fn is_char_boundary(&self, index: usize) -> bool {
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if index == self.len() { return true; }
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// 0 and len are always ok.
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// Test for 0 explicitly so that it can optimize out the check
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// easily and skip reading string data for that case.
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if index == 0 || index == self.len() { return true; }
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match self.as_bytes().get(index) {
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match self.as_bytes().get(index) {
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None => false,
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None => false,
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Some(&b) => b < 128 || b >= 192,
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Some(&b) => b < 128 || b >= 192,
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@ -2026,6 +2029,7 @@ impl StrExt for str {
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self.find(pat)
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self.find(pat)
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}
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}
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#[inline]
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fn split_at(&self, mid: usize) -> (&str, &str) {
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fn split_at(&self, mid: usize) -> (&str, &str) {
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// is_char_boundary checks that the index is in [0, .len()]
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// is_char_boundary checks that the index is in [0, .len()]
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if self.is_char_boundary(mid) {
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if self.is_char_boundary(mid) {
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