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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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144 changes: 139 additions & 5 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 @@ -267,18 +268,151 @@ struct is_supported_char_type
> {
};

template <typename UC>
inline FASTFLOAT_CONSTEXPR14 bool
fastfloat_strncasecmp3(UC const *actual_mixedcase,
UC const *expected_lowercase) {
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};
if (cpp20_and_in_constexpr()) {
for (size_t i = 0; i < 3; i++) {
if ((actual_mixedcase[i] | 32) != expected_lowercase[i]) {
return false;
}
return true;
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@IRainman IRainman Jan 20, 2026

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Exit after 1 cycle.

}
} else {
FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 1 || sizeof(UC) == 2) {
::memcpy(&val1, actual_mixedcase, 3 * sizeof(UC));
::memcpy(&val2, expected_lowercase, 3 * sizeof(UC));
val1 |= mask;
val2 |= mask;
return val1 == val2;
}
else FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 4) {
::memcpy(&val1, actual_mixedcase, 2 * sizeof(UC));
::memcpy(&val2, expected_lowercase, 2 * sizeof(UC));
val1 |= mask;
if (val1 != val2) {
return false;
}
return (actual_mixedcase[2] | 32) == (expected_lowercase[2]);
}
else {
return false;
}
}

return true;
}

template <typename UC>
inline FASTFLOAT_CONSTEXPR14 bool
fastfloat_strncasecmp5(UC const *actual_mixedcase,
UC const *expected_lowercase) {
uint64_t mask{0};
uint64_t val1{0}, val2{0};
if (cpp20_and_in_constexpr()) {
for (size_t i = 0; i < 5; i++) {
if ((actual_mixedcase[i] | 32) != expected_lowercase[i]) {
return false;
}
return true;
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@IRainman IRainman Jan 20, 2026

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Also exit after 1 cycle.

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Contributor Author

@sleepingeight sleepingeight Jan 21, 2026

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sorry for the overlook, will raise a fix PR shortly.

}
} else {
FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 1) {
mask = 0x2020202020202020;
::memcpy(&val1, actual_mixedcase, 5 * sizeof(UC));
::memcpy(&val2, expected_lowercase, 5 * sizeof(UC));
val1 |= mask;
val2 |= mask;
return val1 == val2;
}
else FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 2) {
mask = 0x0020002000200020;
::memcpy(&val1, actual_mixedcase, 4 * sizeof(UC));
::memcpy(&val2, expected_lowercase, 4 * sizeof(UC));
val1 |= mask;
if (val1 != val2) {
return false;
}
return (actual_mixedcase[4] | 32) == (expected_lowercase[4]);
}
else FASTFLOAT_IF_CONSTEXPR17(sizeof(UC) == 4) {
mask = 0x0000002000000020;
::memcpy(&val1, actual_mixedcase, 2 * sizeof(UC));
::memcpy(&val2, expected_lowercase, 2 * sizeof(UC));
val1 |= mask;
if (val1 != val2) {
return false;
}
::memcpy(&val1, actual_mixedcase + 2, 2 * sizeof(UC));
::memcpy(&val2, expected_lowercase + 2, 2 * sizeof(UC));
val1 |= mask;
if (val1 != val2) {
return false;
}
return (actual_mixedcase[4] | 32) == (expected_lowercase[4]);
}
else {
return false;
}
}

return true;
}

// Compares two ASCII strings in a case insensitive manner.
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]) {
return false;
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;
}

if (cpp20_and_in_constexpr()) {
for (size_t i = 0; i < length; i++) {
if ((actual_mixedcase[i] | 32) != expected_lowercase[i]) {
return false;
}
return true;
}
} else {
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));
::memcpy(&val2, expected_lowercase + i, sz * sizeof(UC));
val1 |= mask;
val2 |= mask;
if (val1 != val2) {
return false;
}
}
return true;
}
return true;
}

#ifndef FLT_EVAL_METHOD
Expand Down
6 changes: 3 additions & 3 deletions include/fast_float/parse_number.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ from_chars_result_t<UC>
++first;
}
if (last - first >= 3) {
if (fastfloat_strncasecmp(first, str_const_nan<UC>(), 3)) {
if (fastfloat_strncasecmp3(first, str_const_nan<UC>())) {
answer.ptr = (first += 3);
value = minusSign ? -std::numeric_limits<T>::quiet_NaN()
: std::numeric_limits<T>::quiet_NaN();
Expand All @@ -54,9 +54,9 @@ from_chars_result_t<UC>
}
return answer;
}
if (fastfloat_strncasecmp(first, str_const_inf<UC>(), 3)) {
if (fastfloat_strncasecmp3(first, str_const_inf<UC>())) {
if ((last - first >= 8) &&
fastfloat_strncasecmp(first + 3, str_const_inf<UC>() + 3, 5)) {
fastfloat_strncasecmp5(first + 3, str_const_inf<UC>() + 3)) {
answer.ptr = first + 8;
} else {
answer.ptr = first + 3;
Expand Down