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fix constexpr for umul128.

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This commit is contained in:
HedgehogInTheCPP 2026-08-21 17:11:02 +03:00
parent 8351519606
commit cbdea5e381
1 changed files with 14 additions and 13 deletions
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27
include/fast_float/float_common.h
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@ -637,6 +637,19 @@ fastfloat_really_inline constexpr uint64_t emulu(uint32_t x,
fastfloat_really_inline FASTFLOAT_CONSTEXPR14 uint64_t
umul128(uint64_t ab, uint64_t cd, uint64_t &hi) noexcept {
if (is_constant_evaluated()) {
auto ab_shifted = static_cast<uint32_t>(ab >> 32);
auto cd_shifted = static_cast<uint32_t>(cd >> 32);
auto ad = emulu(ab_shifted, static_cast<uint32_t>(cd));
auto bd = emulu(static_cast<uint32_t>(ab), static_cast<uint32_t>(cd));
auto adbc = ad + emulu(static_cast<uint32_t>(ab), cd_shifted);
auto adbc_carry = static_cast<uint64_t>(adbc < ad) << 32;
auto lo = bd + (adbc << 32);
hi = emulu(ab_shifted, cd_shifted) + static_cast<uint32_t>(adbc >> 32) +
adbc_carry + static_cast<uint64_t>(lo < bd);
return lo;
}
#if defined(_M_ARM64) && !defined(__MINGW32__)
// ARM64 has native support for 64-bit multiplications, no need to emulate
// But MinGW on ARM64 doesn't have native support for 64-bit multiplications
@ -644,19 +657,7 @@ umul128(uint64_t ab, uint64_t cd, uint64_t &hi) noexcept {
return ab * cd;
#elif (defined(_WIN64) && !defined(__clang__) && !defined(_M_ARM64) && \
!defined(__GNUC__))
return _umul128(ab, cd, &hi); // _umul128 not available on ARM64
#else
auto ab_shifted = static_cast<uint32_t>(ab >> 32);
auto cd_shifted = static_cast<uint32_t>(cd >> 32);
auto ad = emulu(ab_shifted, static_cast<uint32_t>(cd));
auto bd = emulu(static_cast<uint32_t>(ab), static_cast<uint32_t>(cd));
auto adbc = ad + emulu(static_cast<uint32_t>(ab), cd_shifted);
auto adbc_carry = static_cast<uint64_t>(adbc < ad) << 32;
auto lo = bd + (adbc << 32);
hi = emulu(ab_shifted, cd_shifted) + static_cast<uint32_t>(adbc >> 32) +
adbc_carry + static_cast<uint64_t>(lo < bd);
return lo;
return _umul128(ab, cd, &hi); // _umul128 not available on ARM64
#endif
}