Repo created

TMessagesProj/jni/voip/webrtc/base/bits.h

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+// 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 <type_traits>
+
+#include "base/compiler_specific.h"
+#include "base/logging.h"
+#include "build/build_config.h"
+
+#if defined(COMPILER_MSVC)
+#include <intrin.h>
+#endif
+
+namespace base {
+namespace bits {
+
+// Returns true iff |value| is a power of 2.
+template <typename T,
+          typename = typename std::enable_if<std::is_integral<T>::value>>
+constexpr inline bool IsPowerOfTwo(T value) {
+  // From "Hacker's Delight": Section 2.1 Manipulating Rightmost Bits.
+  //
+  // Only positive integers with a single bit set are powers of two. If only one
+  // bit is set in x (e.g. 0b00000100000000) then |x-1| will have that bit set
+  // to zero and all bits to its right set to 1 (e.g. 0b00000011111111). Hence
+  // |x & (x-1)| is 0 iff x is a power of two.
+  return value > 0 && (value & (value - 1)) == 0;
+}
+
+// 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(IsPowerOfTwo(alignment));
+  return (size + alignment - 1) & ~(alignment - 1);
+}
+
+// Round down |size| to a multiple of alignment, which must be a power of two.
+inline size_t AlignDown(size_t size, size_t alignment) {
+  DCHECK(IsPowerOfTwo(alignment));
+  return size & ~(alignment - 1);
+}
+
+// CountLeadingZeroBits(value) returns the number of zero bits following the
+// most significant 1 bit in |value| if |value| is non-zero, otherwise it
+// returns {sizeof(T) * 8}.
+// Example: 00100010 -> 2
+//
+// CountTrailingZeroBits(value) returns the number of zero bits preceding the
+// least significant 1 bit in |value| if |value| is non-zero, otherwise it
+// returns {sizeof(T) * 8}.
+// Example: 00100010 -> 1
+//
+// 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)
+
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 4,
+                            unsigned>::type
+    CountLeadingZeroBits(T x) {
+  static_assert(bits > 0, "invalid instantiation");
+  unsigned long index;
+  return LIKELY(_BitScanReverse(&index, static_cast<uint32_t>(x)))
+             ? (31 - index - (32 - bits))
+             : bits;
+}
+
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) == 8,
+                            unsigned>::type
+    CountLeadingZeroBits(T x) {
+  static_assert(bits > 0, "invalid instantiation");
+  unsigned long index;
+// MSVC only supplies _BitScanReverse64 when building for a 64-bit target.
+#if defined(ARCH_CPU_64_BITS)
+  return LIKELY(_BitScanReverse64(&index, static_cast<uint64_t>(x)))
+             ? (63 - index)
+             : 64;
+#else
+  uint32_t left = static_cast<uint32_t>(x >> 32);
+  if (LIKELY(_BitScanReverse(&index, left)))
+    return 31 - index;
+
+  uint32_t right = static_cast<uint32_t>(x);
+  if (LIKELY(_BitScanReverse(&index, right)))
+    return 63 - index;
+
+  return 64;
+#endif
+}
+
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 4,
+                            unsigned>::type
+    CountTrailingZeroBits(T x) {
+  static_assert(bits > 0, "invalid instantiation");
+  unsigned long index;
+  return LIKELY(_BitScanForward(&index, static_cast<uint32_t>(x))) ? index
+                                                                   : bits;
+}
+
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) == 8,
+                            unsigned>::type
+    CountTrailingZeroBits(T x) {
+  static_assert(bits > 0, "invalid instantiation");
+  unsigned long index;
+// MSVC only supplies _BitScanForward64 when building for a 64-bit target.
+#if defined(ARCH_CPU_64_BITS)
+  return LIKELY(_BitScanForward64(&index, static_cast<uint64_t>(x))) ? index
+                                                                     : 64;
+#else
+  uint32_t right = static_cast<uint32_t>(x);
+  if (LIKELY(_BitScanForward(&index, right)))
+    return index;
+
+  uint32_t left = static_cast<uint32_t>(x >> 32);
+  if (LIKELY(_BitScanForward(&index, left)))
+    return 32 + index;
+
+  return 64;
+#endif
+}
+
+ALWAYS_INLINE uint32_t CountLeadingZeroBits32(uint32_t x) {
+  return CountLeadingZeroBits(x);
+}
+
+ALWAYS_INLINE uint64_t CountLeadingZeroBits64(uint64_t x) {
+  return CountLeadingZeroBits(x);
+}
+
+#elif defined(COMPILER_GCC)
+
+// __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.
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 8,
+                            unsigned>::type
+    CountLeadingZeroBits(T value) {
+  static_assert(bits > 0, "invalid instantiation");
+  return LIKELY(value)
+             ? bits == 64
+                   ? __builtin_clzll(static_cast<uint64_t>(value))
+                   : __builtin_clz(static_cast<uint32_t>(value)) - (32 - bits)
+             : bits;
+}
+
+template <typename T, unsigned bits = sizeof(T) * 8>
+ALWAYS_INLINE
+    typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 8,
+                            unsigned>::type
+    CountTrailingZeroBits(T value) {
+  return LIKELY(value) ? bits == 64
+                             ? __builtin_ctzll(static_cast<uint64_t>(value))
+                             : __builtin_ctz(static_cast<uint32_t>(value))
+                       : bits;
+}
+
+ALWAYS_INLINE uint32_t CountLeadingZeroBits32(uint32_t x) {
+  return CountLeadingZeroBits(x);
+}
+
+ALWAYS_INLINE uint64_t CountLeadingZeroBits64(uint64_t x) {
+  return CountLeadingZeroBits(x);
+}
+
+#endif
+
+ALWAYS_INLINE size_t CountLeadingZeroBitsSizeT(size_t x) {
+  return CountLeadingZeroBits(x);
+}
+
+ALWAYS_INLINE size_t CountTrailingZeroBitsSizeT(size_t x) {
+  return CountTrailingZeroBits(x);
+}
+
+// Returns the integer i such as 2^i <= n < 2^(i+1)
+inline int Log2Floor(uint32_t n) {
+  return 31 - CountLeadingZeroBits(n);
+}
+
+// Returns the integer i such as 2^(i-1) < n <= 2^i
+inline int Log2Ceiling(uint32_t n) {
+  // When n == 0, we want the function to return -1.
+  // When n == 0, (n - 1) will underflow to 0xFFFFFFFF, which is
+  // why the statement below starts with (n ? 32 : -1).
+  return (n ? 32 : -1) - CountLeadingZeroBits(n - 1);
+}
+
+}  // namespace bits
+}  // namespace base
+
+#endif  // BASE_BITS_H_