Move SaturatedArithmetic from Blink to base

base/numerics/saturated_arithmetic.h

+// Copyright 2016 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.
+
+#ifndef BASE_NUMERICS_SATURATED_ARITHMETIC_H_
+#define BASE_NUMERICS_SATURATED_ARITHMETIC_H_
+
+#include <stdint.h>
+
+#include <limits>
+
+#include "base/compiler_specific.h"
+
+#if defined(ARCH_CPU_ARM_FAMILY) && defined(COMPILER_GCC) && __OPTIMIZE__
+
+// If we're building ARM on GCC we replace the C++ versions with some
+// native ARM assembly for speed.
+#include "base/numerics/saturated_arithmetic_arm.h"
+
+#else
+
+namespace base {
+
+inline int32_t SaturatedAddition(int32_t a, int32_t b) {
+  uint32_t ua = a;
+  uint32_t ub = b;
+  uint32_t result = ua + ub;
+
+  // Can only overflow if the signed bit of the two values match. If the
+  // signed bit of the result and one of the values differ it overflowed.
+  // The branch compiles to a CMOVNS instruction on x86.
+  if (~(ua ^ ub) & (result ^ ua) & (1 << 31))
+    return std::numeric_limits<int>::max() + (ua >> 31);
+
+  return result;
+}
+
+inline int32_t SaturatedSubtraction(int32_t a, int32_t b) {
+  uint32_t ua = a;
+  uint32_t ub = b;
+  uint32_t result = ua - ub;
+
+  // Can only overflow if the signed bit of the two input values differ. If
+  // the signed bit of the result and the first value differ it overflowed.
+  // The branch compiles to a CMOVNS instruction on x86.
+  if ((ua ^ ub) & (result ^ ua) & (1 << 31))
+    return std::numeric_limits<int>::max() + (ua >> 31);
+
+  return result;
+}
+
+inline int32_t SaturatedNegative(int32_t a) {
+  if (UNLIKELY(a == std::numeric_limits<int>::min()))
+    return std::numeric_limits<int>::max();
+  return -a;
+}
+
+inline int GetMaxSaturatedSetResultForTesting(int fractional_shift) {
+  // For C version the set function maxes out to max int, this differs from
+  // the ARM asm version, see saturated_arithmetic_arm.h for the equivalent asm
+  // version.
+  return std::numeric_limits<int>::max();
+}
+
+inline int GetMinSaturatedSetResultForTesting(int fractional_shift) {
+  return std::numeric_limits<int>::min();
+}
+
+template <int fractional_shift>
+inline int SaturatedSet(int value) {
+  const int kIntMaxForLayoutUnit =

[esprehn, 2016/11/14 22:26:06]

Should probably give these better names not specific to layout unit?

+      std::numeric_limits<int>::max() >> fractional_shift;
+
+  const int kIntMinForLayoutUnit =
+      std::numeric_limits<int>::min() >> fractional_shift;
+
+  if (value > kIntMaxForLayoutUnit)
+    return std::numeric_limits<int>::max();
+
+  if (value < kIntMinForLayoutUnit)
+    return std::numeric_limits<int>::min();
+
+  return value << fractional_shift;
+}
+
+template <int fractional_shift>
+inline int SaturatedSet(unsigned value) {
+  const unsigned kIntMaxForLayoutUnit =
+      std::numeric_limits<int>::max() >> fractional_shift;
+
+  if (value >= kIntMaxForLayoutUnit)
+    return std::numeric_limits<int>::max();
+
+  return value << fractional_shift;
+}
+
+}  // namespace base
+
+#endif  // CPU(ARM) && COMPILER(GCC)
+#endif  // BASE_NUMERICS_SATURATED_ARITHMETIC_H_