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

Part of the plan for WTF, and supports the PartitionAllocator move as well.

BUG=632441
R=dcheng@chromium.org, esprehn@chromium.org

Review URL: https://codereview.chromium.org/2512593002 .

Cr-Commit-Position: refs/heads/master@{#433301}

base/bits.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -10,8 +10,13 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "base/compiler_specific.h"
 #include "base/logging.h"
 
+#if defined(COMPILER_MSVC)
+#include <intrin.h>
+#endif
+
 namespace base {
 namespace bits {
 
@@ -49,6 +54,58 @@ inline size_t Align(size_t size, size_t alignment) {
   return (size + alignment - 1) & ~(alignment - 1);
 }
 
+// These functions count 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.
+#if defined(COMPILER_MSVC)
+
+ALWAYS_INLINE uint32_t CountLeadingZeroBits32(uint32_t x) {
+  unsigned long index;
+  return LIKELY(_BitScanReverse(&index, x)) ? (31 - index) : 32;
+}
+
+#if defined(ARCH_CPU_64_BITS)
+
+// MSVC only supplies _BitScanForward64 when building for a 64-bit target.
+ALWAYS_INLINE uint64_t CountLeadingZeroBits64(uint64_t x) {
+  unsigned long index;
+  return LIKELY(_BitScanReverse64(&index, x)) ? (63 - index) : 64;
+}
+
+#endif
+
+#elif defined(COMPILER_GCC)
+
+// This is very annoying. __builtin_clz has undefined behaviour for an input of
+// 0, even though there's clearly a return value that makes sense, and even
+// though some 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 CountLeadingZeroBits32(uint32_t x) {
+  return LIKELY(x) ? __builtin_clz(x) : 32;
+}
+
+ALWAYS_INLINE uint64_t CountLeadingZeroBits64(uint64_t x) {
+  return LIKELY(x) ? __builtin_clzll(x) : 64;
+}
+
+#endif
+
+#if defined(ARCH_CPU_64_BITS)
+
+ALWAYS_INLINE size_t CountLeadingZeroBitsSizeT(size_t x) {
+  return CountLeadingZeroBits64(x);
+}
+
+#else
+
+ALWAYS_INLINE size_t CountLeadingZeroBitsSizeT(size_t x) {
+  return CountLeadingZeroBits32(x);
+}
+
+#endif
+
 }  // namespace bits
 }  // namespace base
 

base/bits_unittest.cc

@@ -61,5 +61,25 @@ TEST(BitsTest, Align) {
   EXPECT_EQ(kSizeTMax / 2 + 1, Align(1, kSizeTMax / 2 + 1));
 }
 
+TEST(BitsTest, CLZWorks) {
+  EXPECT_EQ(32u, CountLeadingZeroBits32(0u));
+  EXPECT_EQ(31u, CountLeadingZeroBits32(1u));
+  EXPECT_EQ(1u, CountLeadingZeroBits32(1u << 30));
+  EXPECT_EQ(0u, CountLeadingZeroBits32(1u << 31));
+
+#if defined(ARCH_CPU_64_BITS)
+  EXPECT_EQ(64u, CountLeadingZeroBitsSizeT(0ull));
+  EXPECT_EQ(63u, CountLeadingZeroBitsSizeT(1ull));
+  EXPECT_EQ(32u, CountLeadingZeroBitsSizeT(1ull << 31));
+  EXPECT_EQ(1u, CountLeadingZeroBitsSizeT(1ull << 62));
+  EXPECT_EQ(0u, CountLeadingZeroBitsSizeT(1ull << 63));
+#else
+  EXPECT_EQ(32u, CountLeadingZeroBitsSizeT(0u));
+  EXPECT_EQ(31u, CountLeadingZeroBitsSizeT(1u));
+  EXPECT_EQ(1u, CountLeadingZeroBitsSizeT(1u << 30));
+  EXPECT_EQ(0u, CountLeadingZeroBitsSizeT(1u << 31));
+#endif
+}
+
 }  // namespace bits
 }  // namespace base

third_party/WebKit/Source/wtf/BitwiseOperations.h

@@ -28,72 +28,23 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// TODO(palmer): The only caller of this code in Blink is PartitionAlloc. When
+// PA is moved to base, we can remove this file.
+// https://bugs.chromium.org/p/chromium/issues/detail?id=632441
+
 #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
 
 namespace WTF {
 
-#if COMPILER(MSVC)
-
-ALWAYS_INLINE uint32_t countLeadingZeros32(uint32_t x) {
-  unsigned long index;
-  return LIKELY(_BitScanReverse(&index, x)) ? (31 - index) : 32;
-}
+using base::bits::CountLeadingZeroBits32;
+using base::bits::CountLeadingZeroBitsSizeT;
 
 #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;
-}
-
-#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 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);
-}
-
+using base::bits::CountLeadingZeroBits64;
 #endif
 
 }  // namespace WTF

third_party/WebKit/Source/wtf/DEPS

@@ -3,6 +3,7 @@ include_rules = [
     # directories and files instead of writing 'base/'.
     "+base/auto_reset.h",
     "+base/bind.h",
+    "+base/bits.h",
     "+base/compiler_specific.h",
     "+base/debug",
     "+base/logging.h",

third_party/WebKit/Source/wtf/allocator/PartitionAlloc.h

@@ -799,7 +799,7 @@ ALWAYS_INLINE void partitionFree(void* ptr) {
 ALWAYS_INLINE PartitionBucket* partitionGenericSizeToBucket(
     PartitionRootGeneric* root,
     size_t size) {
-  size_t order = kBitsPerSizet - countLeadingZerosSizet(size);
+  size_t order = kBitsPerSizet - CountLeadingZeroBitsSizeT(size);
   // The order index is simply the next few bits after the most significant bit.
   size_t orderIndex = (size >> root->orderIndexShifts[order]) &
                       (kGenericNumBucketsPerOrder - 1);

third_party/WebKit/Source/wtf/allocator/PartitionAllocTest.cpp

@@ -2113,30 +2113,6 @@ TEST(PartitionAllocTest, PurgeDiscardable) {
   TestShutdown();
 }
 
-// Tests that the countLeadingZeros() functions work to our satisfaction.
-// It doesn't seem worth the overhead of a whole new file for these tests, so
-// we'll put them here since partitionAllocGeneric will depend heavily on these
-// functions working correctly.
-TEST(PartitionAllocTest, CLZWorks) {
-  EXPECT_EQ(32u, countLeadingZeros32(0u));
-  EXPECT_EQ(31u, countLeadingZeros32(1u));
-  EXPECT_EQ(1u, countLeadingZeros32(1u << 30));
-  EXPECT_EQ(0u, countLeadingZeros32(1u << 31));
-
-#if CPU(64BIT)
-  EXPECT_EQ(64u, countLeadingZerosSizet(0ull));
-  EXPECT_EQ(63u, countLeadingZerosSizet(1ull));
-  EXPECT_EQ(32u, countLeadingZerosSizet(1ull << 31));
-  EXPECT_EQ(1u, countLeadingZerosSizet(1ull << 62));
-  EXPECT_EQ(0u, countLeadingZerosSizet(1ull << 63));
-#else
-  EXPECT_EQ(32u, countLeadingZerosSizet(0u));
-  EXPECT_EQ(31u, countLeadingZerosSizet(1u));
-  EXPECT_EQ(1u, countLeadingZerosSizet(1u << 30));
-  EXPECT_EQ(0u, countLeadingZerosSizet(1u << 31));
-#endif
-}
-
 }  // namespace WTF
 
 #endif  // !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)