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Use MSVC intrinsics for better performance #116

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Feb 20, 2015
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Use MSVC intrinsics for better performance #116

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34 changes: 31 additions & 3 deletions format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,13 @@
#if _SECURE_SCL
# include <iterator>
#endif
#ifdef _MSC_VER
# include <intrin.h> // _BitScanForward, _BitScanForward64
# pragma intrinsic(_BitScanForward)
# ifdef _WIN64
# pragma intrinsic(_BitScanForward64)
# endif
#endif

#ifdef __GNUC__
# define FMT_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
Expand Down Expand Up @@ -539,7 +546,25 @@ struct BasicData {

typedef BasicData<> Data;

#if FMT_GCC_VERSION >= 400 || FMT_HAS_BUILTIN(__builtin_clzll)
#if _MSC_VER
# ifdef _WIN64
# define FMT_EFFICIENT_COUNT_DIGITS
inline unsigned count_digits(uint64_t n) {
uint32_t index;
assert(__BitScanForward64(&index, n | 1));
unsigned t = (64 - index) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_64[t]) + 1;
}
# endif
inline unsigned count_digits(uint32_t n) {
uint32_t index;
assert(__BitScanForward(&index, n | 1));
unsigned t = (32 - index) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_32[t]) + 1;
}
#elif FMT_GCC_VERSION >= 400 || defined __clang__
# if FMT_HAS_BUILTIN(__builtin_clzll)
# define FMT_EFFICIENT_COUNT_DIGITS
// Returns the number of decimal digits in n. Leading zeros are not counted
// except for n == 0 in which case count_digits returns 1.
inline unsigned count_digits(uint64_t n) {
Expand All @@ -548,14 +573,17 @@ inline unsigned count_digits(uint64_t n) {
unsigned t = (64 - __builtin_clzll(n | 1)) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_64[t]) + 1;
}
# if FMT_GCC_VERSION >= 400 || FMT_HAS_BUILTIN(__builtin_clz)
# endif
# if FMT_HAS_BUILTIN(__builtin_clz)
// Optional version of count_digits for better performance on 32-bit platforms.
inline unsigned count_digits(uint32_t n) {
uint32_t t = (32 - __builtin_clz(n | 1)) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_32[t]) + 1;
}
# endif
#else
#endif

#ifndef FMT_EFFICIENT_COUNT_DIGITS
// Fallback version of count_digits used when __builtin_clz is not available.
inline unsigned count_digits(uint64_t n) {
unsigned count = 1;
Expand Down