From 6ff2db181f3dc8a9c95f6f9564c0bb1db7cae8e3 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Thu, 21 Jan 2021 03:48:32 -0500
Subject: [PATCH] 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.
---
src/common/bit_util.h | 50 ++++++++++++-------------------------------
1 file changed, 14 insertions(+), 36 deletions(-)
diff --git a/src/common/bit_util.h b/src/common/bit_util.h
index 685e7fc9be..69fb4e5e4e 100644
--- a/src/common/bit_util.h
+++ b/src/common/bit_util.h
@@ -7,10 +7,6 @@
#include <climits>
#include <cstddef>
-#ifdef _MSC_VER
-#include <intrin.h>
-#endif
-
#include "common/common_types.h"
namespace Common {
@@ -21,48 +17,30 @@ template <typename T>
return sizeof(T) * CHAR_BIT;
}
-#ifdef _MSC_VER
-
-[[nodiscard]] inline u32 MostSignificantBit32(const u32 value) {
- unsigned long result;
- _BitScanReverse(&result, value);
- return static_cast<u32>(result);
+[[nodiscard]] constexpr u32 MostSignificantBit32(const u32 value) {
+ return 31U - static_cast<u32>(std::countl_zero(value));
}
-[[nodiscard]] inline u32 MostSignificantBit64(const u64 value) {
- unsigned long result;
- _BitScanReverse64(&result, value);
- return static_cast<u32>(result);
+[[nodiscard]] constexpr u32 MostSignificantBit64(const u64 value) {
+ return 63U - static_cast<u32>(std::countl_zero(value));
}
-#else
-
-[[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) {
+[[nodiscard]] constexpr u32 Log2Floor32(const u32 value) {
return MostSignificantBit32(value);
}
-[[nodiscard]] inline u32 Log2Ceil32(const u32 value) {
- const u32 log2_f = Log2Floor32(value);
- return log2_f + ((value ^ (1U << log2_f)) != 0U);
-}
-
-[[nodiscard]] inline u32 Log2Floor64(const u64 value) {
+[[nodiscard]] constexpr u32 Log2Floor64(const u64 value) {
return MostSignificantBit64(value);
}
-[[nodiscard]] inline u32 Log2Ceil64(const u64 value) {
- const u64 log2_f = static_cast<u64>(Log2Floor64(value));
- return static_cast<u32>(log2_f + ((value ^ (1ULL << log2_f)) != 0ULL));
+[[nodiscard]] constexpr u32 Log2Ceil32(const u32 value) {
+ const u32 log2_f = Log2Floor32(value);
+ 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