1 files changed, 114 insertions, 0 deletions
diff --git a/third_party/base/bits.h b/third_party/base/bits.h
new file mode 100644
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--- /dev/null
+++ b/third_party/base/bits.h
@@ -0,0 +1,114 @@
+// 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.
+
+// This file defines some bit utilities.
+
+#ifndef BASE_BITS_H_
+#define BASE_BITS_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "third_party/base/compiler_specific.h"
+#include "third_party/base/logging.h"
+
+#if defined(COMPILER_MSVC)
+#include <intrin.h>
+#endif
+
+namespace pdfium {
+namespace base {
+namespace bits {
+
+// Returns the integer i such as 2^i <= n < 2^(i+1)
+inline int Log2Floor(uint32_t n) {
+  if (n == 0)
+    return -1;
+  int log = 0;
+  uint32_t value = n;
+  for (int i = 4; i >= 0; --i) {
+    int shift = (1 << i);
+    uint32_t x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  DCHECK_EQ(value, 1u);
+  return log;
+}
+
+// Returns the integer i such as 2^(i-1) < n <= 2^i
+inline int Log2Ceiling(uint32_t n) {
+  if (n == 0) {
+    return -1;
+  } else {
+    // Log2Floor returns -1 for 0, so the following works correctly for n=1.
+    return 1 + Log2Floor(n - 1);
+  }
+}
+
+// Round up |size| to a multiple of alignment, which must be a power of two.
+inline size_t Align(size_t size, size_t alignment) {
+  DCHECK_EQ(alignment & (alignment - 1), 0u);
+  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
+}  // namespace pdfium
+
+#endif  // BASE_BITS_H_