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Use correct intrinsics for count_digits

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This commit is contained in:
Victor Zverovich 2015-02-20 08:49:06 -08:00
parent 939193be21
commit 27e0bf72c0
1 changed files with 34 additions and 29 deletions
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63
format.h
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@ -43,12 +43,30 @@
#if _SECURE_SCL
# include <iterator>
#endif
#ifdef _MSC_VER
# include <intrin.h> // _BitScanForward, _BitScanForward64
# pragma intrinsic(_BitScanForward)
# include <intrin.h> // _BitScanReverse, _BitScanReverse64
namespace fmt {
namespace internal {
# pragma intrinsic(_BitScanReverse)
# ifdef _WIN64
# pragma intrinsic(_BitScanForward64)
# pragma intrinsic(_BitScanReverse64)
inline uint32_t builtin_clzll(uint64_t n) {
unsigned long r = 0;
_BitScanReverse64(&r, x);
return 63 - r;
}
# define FMT_BUILTIN_CLZLL(n) fmt::internal::builtin_clzll(n)
# endif
inline uint32_t builtin_clz(uint32_t x) {
unsigned long r = 0;
_BitScanReverse(&r, x);
return 31 - r;
}
# define FMT_BUILTIN_CLZ(n) fmt::internal::builtin_clz(n)
}
}
#endif
#ifdef __GNUC__
@ -546,44 +564,31 @@ struct BasicData {
typedef BasicData<> Data;
#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
#if FMT_GCC_VERSION >= 400 || FMT_HAS_BUILTIN(__builtin_clz)
# define FMT_BUILTIN_CLZ(n) __builtin_clzll(n)
#endif
#if FMT_GCC_VERSION >= 400 || FMT_HAS_BUILTIN(__builtin_clzll)
# define FMT_BUILTIN_CLZLL(n) __builtin_clzll(n)
#endif
#ifdef FMT_BUILTIN_CLZLL
// 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) {
// Based on http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
// and the benchmark https://github.com/localvoid/cxx-benchmark-count-digits.
unsigned t = (64 - __builtin_clzll(n | 1)) * 1233 >> 12;
unsigned t = (64 - FMT_BUILTIN_CLZLL(n | 1)) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_64[t]) + 1;
}
# endif
# if FMT_HAS_BUILTIN(__builtin_clz)
# ifdef FMT_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;
uint32_t t = (32 - FMT_BUILTIN_CLZ(n | 1)) * 1233 >> 12;
return t - (n < Data::POWERS_OF_10_32[t]) + 1;
}
# endif
#endif
#ifndef FMT_EFFICIENT_COUNT_DIGITS
#else
// Fallback version of count_digits used when __builtin_clz is not available.
inline unsigned count_digits(uint64_t n) {
unsigned count = 1;