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fast_float_parser.h: copy nlz_int64 from the bigdecimal gem #1012

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Merged
byroot merged 1 commit into from
Jun 16, 2026
+21 −5
Merged

fast_float_parser.h: copy nlz_int64 from the bigdecimal gem #1012

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26 changes: 21 additions & 5 deletions ext/json/ext/vendor/fast_float_parser.h
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Original file line number Diff line number Diff line change
Expand Up @@ -713,21 +713,37 @@ static inline double ffp_bits2double(uint64_t bits) {
# include <intrin.h>
#endif

#if defined(_MSC_VER) && defined(__AVX2__)
# pragma intrinsic(__lzcnt64)
#endif

static inline unsigned int
ffc_nlz_int64(uint64_t x)
{
#if defined(_MSC_VER) && defined(__AVX2__)
#if defined(_MSC_VER) && defined(__AVX2__) && defined(HAVE___LZCNT64)
return (unsigned int)__lzcnt64(x);

#elif defined(__x86_64__) && defined(__LZCNT__)
#elif defined(__x86_64__) && defined(__LZCNT__) && defined(HAVE__LZCNT_U64)
return (unsigned int)_lzcnt_u64(x);

#elif defined(_WIN64) && defined(_MSC_VER) /* &&! defined(__AVX2__) */
#elif defined(_WIN64) && defined(_MSC_VER) && defined(HAVE__BITSCANREVERSE64)
unsigned long r;
return _BitScanReverse64(&r, x) ? (63u - (unsigned int)r) : 64;

#elif defined(__has_builtin) && __has_builtin(__builtin_clzll)
return (unsigned int)__builtin_clzll((unsigned long long)x);
#elif __has_builtin(__builtin_clzl) && __has_builtin(__builtin_clzll) && !(defined(__sun) && defined(__sparc))
if (x == 0) {
return 64;
}
else if (sizeof(long) * CHAR_BIT == 64) {
return (unsigned int)__builtin_clzl((unsigned long)x);
}
else if (sizeof(long long) * CHAR_BIT == 64) {
return (unsigned int)__builtin_clzll((unsigned long long)x);
}
else {
/* :FIXME: Is there a way to make this branch a compile-time error? */
__builtin_unreachable();
}

#else
uint64_t y;
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