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bit_util: Unify implementations of MostSignificantBit32/MostSignificantBit64 

We can use the standardized CLZ facilities to perform this. This also
allows us to make utilizing functions constexpr and eliminate the
inclusion of an intrinsics header.
This commit is contained in:
Lioncash 2021-01-21 03:48:32 -05:00
parent e8401964b4
commit 6ff2db181f
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