gfx: Converge scale precision related differences to single class.

ui/gfx/geometry/scale.cc

+// Copyright (c) 2015 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.
+
+#include "ui/gfx/geometry/scale.h"
+
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "base/numerics/safe_math.h"
+#include "ui/gfx/switches.h"
+
+namespace {
+const int kScalePrecision = 4;
+
+bool VerifyFixedPrecisionValue(float value) {
+  const base::CheckedNumeric<float> checked_factor = pow(10, kScalePrecision);
+  if (!checked_factor.IsValid())
+    return false;
+
+  base::CheckedNumeric<float> checked_value = value;
+  checked_value *= checked_factor.ValueOrDie();
+  if (!checked_value.IsValid())
+    return false;
+
+  checked_value = floor(checked_value.ValueOrDie());
+  checked_value /= checked_factor.ValueOrDie();
+  return checked_value.IsValid();
+}
+
+float ComputeFixedPrecisionValue(float value) {
+  // Limiting precision 1 <= kScalePrecision <= 8, as floating point precision
+  // of >= 12 gives different values, 8 on a safer side.
+  DCHECK(kScalePrecision >= 1 && kScalePrecision <= 8);
+  DCHECK(VerifyFixedPrecisionValue(value));
+
+  const float factor = pow(10, kScalePrecision);
+  value *= factor;
+  value = floor(value);
+  value /= factor;
+  return value;
+}
+
+bool IsFixedPrecisionScaleEnabled() {
+  static bool fixed_precision_enabled =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableFixedPrecisionScale);
+  return fixed_precision_enabled;
+}
+
+}  // namespace
+
+namespace gfx {
+
+Scale::Scale(float value) : absolute_value_(value) {
+  // Scale < 0.0f is undefined.
+  DCHECK(absolute_value_ >= 0);
+  DCHECK_LT(absolute_value_, std::numeric_limits<float>::max());
+
+  if (IsFixedPrecisionScaleEnabled())
+    value_ = ComputeFixedPrecisionValue(absolute_value_);
+  else
+    value_ = absolute_value_;
+}
+
+Scale::Scale(const Scale& other) {
+  absolute_value_ = other.absolute_value_;
+  value_ = other.value_;
+}
+
+Scale& Scale::operator=(const Scale& other) {
+  absolute_value_ = other.absolute_value_;
+  value_ = other.value_;
+  return *this;
+}
+
+bool Scale::operator<(const Scale& other) const {
+  return this->Value() < other.Value();
+}
+
+bool Scale::operator>(const Scale& other) const {
+  return this->Value() > other.Value();
+}
+
+}  // namespace gfx