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Use _BitScanReverse on Win32

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nxtn-staged 2022-12-27 11:23:19 +08:00 • committed by GitHub
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commit 5a8c7606df
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1 changed files with 6 additions and 12 deletions
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18
include/fast_double_parser.h
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@ -193,24 +193,18 @@ really_inline value128 full_multiplication(uint64_t value1, uint64_t value2) {
/* result might be undefined when input_num is zero */
inline int leading_zeroes(uint64_t input_num) {
#ifdef _MSC_VER
#if defined(_M_X64) || defined(_M_ARM64) || defined (_M_IA64)
unsigned long leading_zero = 0;
// Search the mask data from most significant bit (MSB)
// to least significant bit (LSB) for a set bit (1).
#ifdef _WIN64
if (_BitScanReverse64(&leading_zero, input_num))
return (int)(63 - leading_zero);
else
return 64;
#else
int last_bit = 0;
if(input_num & uint64_t(0xffffffff00000000)) input_num >>= 32, last_bit |= 32;
if(input_num & uint64_t( 0xffff0000)) input_num >>= 16, last_bit |= 16;
if(input_num & uint64_t( 0xff00)) input_num >>= 8, last_bit |= 8;
if(input_num & uint64_t( 0xf0)) input_num >>= 4, last_bit |= 4;
if(input_num & uint64_t( 0xc)) input_num >>= 2, last_bit |= 2;
if(input_num & uint64_t( 0x2)) input_num >>= 1, last_bit |= 1;
return 63 - last_bit;
#endif // defined(_M_X64) || defined(_M_ARM64) || defined (_M_IA64)
if (_BitScanReverse(&leading_zero, (uint32_t)(input_num >> 32)))
return (int)(63 - (leading_zero + 32));
if (_BitScanReverse(&leading_zero, (uint32_t)input_num))
return (int)(63 - leading_zero);
#endif // _WIN64
#else
return __builtin_clzll(input_num);
#endif // _MSC_VER