Motown: Rename Ratio and LinearFunction classes

mojo/services/media/common/cpp/timeline_rate.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 MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_RATE_H_
+#define MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_RATE_H_
+
+#include <stdint.h>
+
+#include <limits>
+
+#include "mojo/public/cpp/environment/logging.h"
+
+namespace mojo {
+namespace media {
+
+// TODO(dalesat): Consider always allowing inexact results.
+
+// Expresses the relative rate of a timeline as the ratio between two uint32_t
+// values subject_delta / reference_delta. "subject" refers to the timeline
+// whose rate is being represented, and "reference" refers to the timeline
+// relative to which the rate is expressed.
+class TimelineRate {
+ public:
+  // Used to indicate overflow of scaling operations.
+  static constexpr int64_t kOverflow = std::numeric_limits<int64_t>::max();
+
+  // Reduces the ratio of *subject_delta and *reference_delta.
+  static void Reduce(uint32_t* subject_delta, uint32_t* reference_delta);
+
+  // Produces the product of the rates. If exact is true, DCHECKs on loss of
+  // precision.
+  static void Product(uint32_t a_subject_delta,
+                      uint32_t a_reference_delta,
+                      uint32_t b_subject_delta,
+                      uint32_t b_reference_delta,
+                      uint32_t* product_subject_delta,
+                      uint32_t* product_reference_delta,
+                      bool exact = true);
+
+  // Produces the product of the rates and the int64_t as an int64_t. Returns
+  // kOverflow on overflow.
+  static int64_t Scale(int64_t value,
+                       uint32_t subject_delta,
+                       uint32_t reference_delta);
+
+  // Returns the product of the rates. If exact is true, DCHECKs on loss of
+  // precision.
+  static TimelineRate Product(const TimelineRate& a,
+                              const TimelineRate& b,
+                              bool exact = true) {
+    uint32_t result_subject_delta;
+    uint32_t result_reference_delta;
+    Product(a.subject_delta(), a.reference_delta(), b.subject_delta(),
+            b.reference_delta(), &result_subject_delta, &result_reference_delta,
+            exact);
+    return TimelineRate(result_subject_delta, result_reference_delta);
+  }
+
+  TimelineRate() : subject_delta_(0), reference_delta_(1) {}
+
+  explicit TimelineRate(uint32_t subject_delta)
+      : subject_delta_(subject_delta), reference_delta_(1) {}
+
+  TimelineRate(uint32_t subject_delta, uint32_t reference_delta)
+      : subject_delta_(subject_delta), reference_delta_(reference_delta) {
+    MOJO_DCHECK(reference_delta != 0);
+    Reduce(&subject_delta_, &reference_delta_);
+  }
+
+  // Returns the inverse of the rate. DCHECKs if the subject_delta of this
+  // rate is zero.
+  TimelineRate Inverse() const {
+    MOJO_DCHECK(subject_delta_ != 0);
+    return TimelineRate(reference_delta_, subject_delta_);
+  }
+
+  // Scales the value by this rate. Returns kOverflow on overflow.
+  int64_t Scale(int64_t value) const {
+    return Scale(value, subject_delta_, reference_delta_);
+  }
+
+  uint32_t subject_delta() const { return subject_delta_; }
+  uint32_t reference_delta() const { return reference_delta_; }
+
+ private:
+  uint32_t subject_delta_;
+  uint32_t reference_delta_;
+};
+
+// Tests two rates for equality.
+inline bool operator==(const TimelineRate& a, const TimelineRate& b) {
+  return a.subject_delta() == b.subject_delta() &&
+         a.reference_delta() == b.reference_delta();
+}
+
+// Tests two rates for inequality.
+inline bool operator!=(const TimelineRate& a, const TimelineRate& b) {
+  return !(a == b);
+}
+
+// Returns the product of the two rates. DCHECKs on loss of precision.
+inline TimelineRate operator*(const TimelineRate& a, const TimelineRate& b) {
+  return TimelineRate::Product(a, b);
+}
+
+// Returns the product of the rate and the int64_t. Returns kOverflow on
+// overflow.
+inline int64_t operator*(const TimelineRate& a, int64_t b) {
+  return a.Scale(b);
+}
+
+// Returns the product of the rate and the int64_t. Returns kOverflow on
+// overflow.
+inline int64_t operator*(int64_t a, const TimelineRate& b) {
+  return b.Scale(a);
+}
+
+// Returns the the int64_t divided by the rate. Returns kOverflow on
+// overflow.
+inline int64_t operator/(int64_t a, const TimelineRate& b) {
+  return b.Inverse().Scale(a);
+}
+
+}  // namespace media
+}  // namespace mojo
+
+#endif  // MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_RATE_H_