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optimize fastfloat_strncasecmp #356

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Merged
lemire merged 2 commits into from
Jan 18, 2026
Merged

optimize fastfloat_strncasecmp #356

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265cb84
optimise fastfloat_strncasecmp
sleepingeight Dec 29, 2025
4eb0d80
add specialisations
sleepingeight Dec 30, 2025
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25 changes: 22 additions & 3 deletions include/fast_float/float_common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
#define FASTFLOAT_FLOAT_COMMON_H

#include <cfloat>
#include <cstddef>
#include <cstdint>
#include <cassert>
#include <cstring>
Expand Down Expand Up @@ -272,9 +273,27 @@ template <typename UC>
inline FASTFLOAT_CONSTEXPR14 bool
fastfloat_strncasecmp(UC const *actual_mixedcase, UC const *expected_lowercase,
size_t length) {
for (size_t i = 0; i < length; ++i) {
UC const actual = actual_mixedcase[i];
if ((actual < 256 ? actual | 32 : actual) != expected_lowercase[i]) {
uint64_t mask{0};
FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 1) { mask = 0x2020202020202020; }
else FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 2) {
mask = 0x0020002000200020;
}
else FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 4) {
mask = 0x0000002000000020;
}
else {
return false;
}
uint64_t val1{0}, val2{0};
size_t sz{8 / (sizeof(UC))};
for (size_t i = 0; i < length; i += sz) {
val1 = val2 = 0;
sz = std::min(sz, length - i);
::memcpy(&val1, actual_mixedcase + i, sz * sizeof(UC));
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@lemire lemire Dec 29, 2025

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this use of memcpy likely breaks the constexpr qualifier. (Easy to fix.)

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@sleepingeight sleepingeight Dec 30, 2025

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I've modified the function to use memcpy only during run time. PTAL.

::memcpy(&val2, expected_lowercase + i, sz * sizeof(UC));
val1 |= mask;
val2 |= mask;
if (val1 != val2) {
return false;
}
}
Expand Down