From 6ff2db181f3dc8a9c95f6f9564c0bb1db7cae8e3 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Thu, 21 Jan 2021 03:48:32 -0500
Subject: 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 | 48 +++++++++++++-----------------------------------
 1 file changed, 13 insertions(+), 35 deletions(-)

(limited to 'src/common')

diff --git a/src/common/bit_util.h b/src/common/bit_util.h
index 685e7fc9b..69fb4e5e4 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]] inline u32 MostSignificantBit64(const u64 value) {
-    unsigned long result;
-    _BitScanReverse64(&result, value);
-    return static_cast<u32>(result);
-}
-
-#else
-
-[[nodiscard]] inline u32 MostSignificantBit32(const u32 value) {
-    return 31U - static_cast<u32>(__builtin_clz(value));
+[[nodiscard]] constexpr u32 MostSignificantBit32(const u32 value) {
+    return 31U - static_cast<u32>(std::countl_zero(value));
 }
 
-[[nodiscard]] inline u32 MostSignificantBit64(const u64 value) {
-    return 63U - static_cast<u32>(__builtin_clzll(value));
+[[nodiscard]] constexpr u32 MostSignificantBit64(const u64 value) {
+    return 63U - static_cast<u32>(std::countl_zero(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]] constexpr u32 Log2Floor64(const u64 value) {
+    return MostSignificantBit64(value);
 }
 
-[[nodiscard]] inline u32 Log2Floor64(const u64 value) {
-    return MostSignificantBit64(value);
+[[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]] 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 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
-- 
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