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Performance optimization for case_fold, second edition #335

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Merged
tzlaine merged 1 commit into from
Oct 24, 2026
Merged

Performance optimization for case_fold, second edition #335

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25 changes: 17 additions & 8 deletions include/boost/parser/detail/case_fold.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -44,16 +44,25 @@ namespace boost::parser::detail {
template<typename I>
I case_fold(char32_t cp, I out)
{
// punctuation, braces, spaces...
if (cp < 0x41) {
*out++ = cp;
return out;
}
// upper case ASCII letters
if (cp <= 0x5a) {
*out++ = cp + 0x20;
return out;
}
// nothing else is mapped before 0xb5
// https://www.unicode.org/Public/UCD/latest/ucd/CaseFolding.txt
if (cp < 0xb5) {
*out++ = cp;
return out;
}
// One-byte fast path.
if (cp < 0x100) {
// ASCII letter fast path.
if (0x61 <= cp && cp <= 0x7a) {
*out++ = cp;
return out;
} else if (0x41 <= cp && cp <= 0x5a) {
*out++ = cp + 0x20;
return out;
} else if (cp == 0x00DF) {
if (cp == 0x00DF) {
// The lone multi-mapping below 0x100.
*out++ = 0x0073;
*out++ = 0x0073;
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