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Merge pull request #5781 from lioncash/bits

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bit_util: Unify implementations of MostSignificantBit32/MostSignificantBit64
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bunnei 2021-01-21 14:45:40 -08:00 committed by GitHub
commit 2c4c7aea8a
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1 changed files with 14 additions and 36 deletions
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50
src/common/bit_util.h
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@ -7,10 +7,6 @@
#include <climits> #include <climits>
#include <cstddef> #include <cstddef>
#ifdef _MSC_VER
#include <intrin.h>
#endif
#include "common/common_types.h" #include "common/common_types.h"
namespace Common { namespace Common {
@ -21,48 +17,30 @@ template <typename T>
return sizeof(T) * CHAR_BIT; return sizeof(T) * CHAR_BIT;
} }
#ifdef _MSC_VER [[nodiscard]] constexpr u32 MostSignificantBit32(const u32 value) {
return 31U - static_cast<u32>(std::countl_zero(value));
[[nodiscard]] inline u32 MostSignificantBit32(const u32 value) {
unsigned long result;
_BitScanReverse(&result, value);
return static_cast<u32>(result);
} }
[[nodiscard]] inline u32 MostSignificantBit64(const u64 value) { [[nodiscard]] constexpr u32 MostSignificantBit64(const u64 value) {
unsigned long result; return 63U - static_cast<u32>(std::countl_zero(value));
_BitScanReverse64(&result, value);
return static_cast<u32>(result);
} }
#else [[nodiscard]] constexpr u32 Log2Floor32(const u32 value) {
[[nodiscard]] inline u32 MostSignificantBit32(const u32 value) {
return 31U - static_cast<u32>(__builtin_clz(value));
}
[[nodiscard]] inline u32 MostSignificantBit64(const u64 value) {
return 63U - static_cast<u32>(__builtin_clzll(value));
}
#endif
[[nodiscard]] inline u32 Log2Floor32(const u32 value) {
return MostSignificantBit32(value); return MostSignificantBit32(value);
} }
[[nodiscard]] inline u32 Log2Ceil32(const u32 value) { [[nodiscard]] constexpr u32 Log2Floor64(const u64 value) {
const u32 log2_f = Log2Floor32(value);
return log2_f + ((value ^ (1U << log2_f)) != 0U);
}
[[nodiscard]] inline u32 Log2Floor64(const u64 value) {
return MostSignificantBit64(value); return MostSignificantBit64(value);
} }
[[nodiscard]] inline u32 Log2Ceil64(const u64 value) { [[nodiscard]] constexpr u32 Log2Ceil32(const u32 value) {
const u64 log2_f = static_cast<u64>(Log2Floor64(value)); const u32 log2_f = Log2Floor32(value);
return static_cast<u32>(log2_f + ((value ^ (1ULL << log2_f)) != 0ULL)); return log2_f + static_cast<u32>((value ^ (1U << log2_f)) != 0U);
}
[[nodiscard]] constexpr u32 Log2Ceil64(const u64 value) {
const u64 log2_f = Log2Floor64(value);
return static_cast<u32>(log2_f + static_cast<u64>((value ^ (1ULL << log2_f)) != 0ULL));
} }
} // namespace Common } // namespace Common