Move wtf/BitwiseOperations.h into base/bits.h.

third_party/WebKit/Source/wtf/BitwiseOperations.h

Index: third_party/WebKit/Source/wtf/BitwiseOperations.h
diff --git a/third_party/WebKit/Source/wtf/BitwiseOperations.h b/third_party/WebKit/Source/wtf/BitwiseOperations.h
index 2e6d2774fe1a002f2e97f16275c70394b6758efa..b3f528120b3fe410e463f78e266f916fc64f2d73 100644
--- a/third_party/WebKit/Source/wtf/BitwiseOperations.h
+++ b/third_party/WebKit/Source/wtf/BitwiseOperations.h
@@ -31,71 +31,27 @@
 #ifndef WTF_BitwiseOperations_h
 #define WTF_BitwiseOperations_h
 
-// DESCRIPTION
-// countLeadingZeros() is a bitwise operation that counts the number of leading
-// zeros in a binary value, starting with the most significant bit. C does not
-// have an operator to do this, but fortunately the various compilers have
-// built-ins that map to fast underlying processor instructions.
-
+#include "base/bits.h"
 #include "wtf/CPU.h"
-#include "wtf/Compiler.h"
-#include <cstddef>
-#include <stdint.h>
 
-#if COMPILER(MSVC)
-#include <intrin.h>
-#endif
+#include <stdint.h>
 
 namespace WTF {
 
-#if COMPILER(MSVC)
-
-ALWAYS_INLINE uint32_t countLeadingZeros32(uint32_t x) {
-  unsigned long index;
-  return LIKELY(_BitScanReverse(&index, x)) ? (31 - index) : 32;
+ALWAYS_INLINE uint32_t CountLeadingZeroBits32(uint32_t x) {
+  return base::bits::CountLeadingZeroBits32(x);

[esprehn, 2016/11/17 07:49:42]

Can we write

using base::bits instead?

 }
 
 #if CPU(64BIT)
-
-// MSVC only supplies _BitScanForward64 when building for a 64-bit target.
-ALWAYS_INLINE uint64_t countLeadingZeros64(uint64_t x) {
-  unsigned long index;
-  return LIKELY(_BitScanReverse64(&index, x)) ? (63 - index) : 64;
+ALWAYS_INLINE uint64_t CountLeadingZeroBits64(uint64_t x) {
+  return base::bits::CountLeadingZeroBits64(x);
 }
-
 #endif
 
-#elif COMPILER(GCC)
-
-// This is very annoying. __builtin_clz has undefined behaviour for an input of
-// 0, even though these's clearly a return value that makes sense, and even
-// though nascent processor clz instructions have defined behaviour for 0.
-// We could drop to raw __asm__ to do better, but we'll avoid doing that unless
-// we see proof that we need to.
-ALWAYS_INLINE uint32_t countLeadingZeros32(uint32_t x) {
-  return LIKELY(x) ? __builtin_clz(x) : 32;
+ALWAYS_INLINE size_t CountLeadingZeroBitsSizeT(size_t x) {
+  return base::bits::CountLeadingZeroBitsSizeT(x);
 }
 
-ALWAYS_INLINE uint64_t countLeadingZeros64(uint64_t x) {
-  return LIKELY(x) ? __builtin_clzll(x) : 64;
-}
-
-#endif
-
-#if CPU(64BIT)
-
-ALWAYS_INLINE size_t countLeadingZerosSizet(size_t x) {
-  return countLeadingZeros64(x);
-}
-
-#else
-
-ALWAYS_INLINE size_t countLeadingZerosSizet(size_t x) {
-  return countLeadingZeros32(x);
-}
-
-#endif
-
 }  // namespace WTF
 
 #endif  // WTF_BitwiseOperations_h