content/common/inter_process_time_ticks_converter.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/common/inter_process_time_ticks_converter.h"
   6
   7 #include "base/logging.h"
   8 #include "base/strings/string_number_conversions.h"
   9
  10 namespace content {
  11
  12 InterProcessTimeTicksConverter::InterProcessTimeTicksConverter(
  13     const LocalTimeTicks& local_lower_bound,
  14     const LocalTimeTicks& local_upper_bound,
  15     const RemoteTimeTicks& remote_lower_bound,
  16     const RemoteTimeTicks& remote_upper_bound)
  17     : remote_lower_bound_(remote_lower_bound.value_),
  18       remote_upper_bound_(remote_upper_bound.value_) {
  19   int64 target_range = local_upper_bound.value_ - local_lower_bound.value_;
  20   int64 source_range = remote_upper_bound.value_ - remote_lower_bound.value_;
  21   DCHECK_GE(target_range, 0);
  22   DCHECK_GE(source_range, 0);
  23   if (source_range <= target_range) {
  24     // We fit!  Center the source range on the target range.
  25     numerator_ = 1;
  26     denominator_ = 1;
  27     local_base_time_ =
  28         local_lower_bound.value_ + (target_range - source_range) / 2;
  29     // When converting times, remote bounds should fall within local bounds.
  30     DCHECK_LE(local_lower_bound.value_,
  31               ToLocalTimeTicks(remote_lower_bound).value_);
  32     DCHECK_GE(local_upper_bound.value_,
  33               ToLocalTimeTicks(remote_upper_bound).value_);
  34     return;
  35   }
  36
  37   // Interpolate values so that remote range will be will exactly fit into the
  38   // local range, if possible.
  39   numerator_ = target_range;
  40   denominator_ = source_range;
  41   local_base_time_ = local_lower_bound.value_;
  42   // When converting times, remote bounds should equal local bounds.
  43   DCHECK_EQ(local_lower_bound.value_,
  44             ToLocalTimeTicks(remote_lower_bound).value_);
  45   DCHECK_EQ(local_upper_bound.value_,
  46             ToLocalTimeTicks(remote_upper_bound).value_);
  47   DCHECK_EQ(target_range, Convert(source_range));
  48 }
  49
  50 LocalTimeTicks InterProcessTimeTicksConverter::ToLocalTimeTicks(
  51     const RemoteTimeTicks& remote_ms) const {
  52   // If input time is "null", return another "null" time.
  53   if (remote_ms.value_ == 0)
  54     return LocalTimeTicks(0);
  55   DCHECK_LE(remote_lower_bound_, remote_ms.value_);
  56   DCHECK_GE(remote_upper_bound_, remote_ms.value_);
  57   RemoteTimeDelta remote_delta = remote_ms - remote_lower_bound_;
  58   return LocalTimeTicks(local_base_time_ +
  59                         ToLocalTimeDelta(remote_delta).value_);
  60 }
  61
  62 LocalTimeDelta InterProcessTimeTicksConverter::ToLocalTimeDelta(
  63     const RemoteTimeDelta& remote_delta) const {
  64   DCHECK_GE(remote_upper_bound_, remote_lower_bound_ + remote_delta.value_);
  65   return LocalTimeDelta(Convert(remote_delta.value_));
  66 }
  67
  68 int64 InterProcessTimeTicksConverter::Convert(int64 value) const {
  69   if (value <= 0) {
  70     return value;
  71   }
  72   return numerator_ * value / denominator_;
  73 }
  74
  75 bool InterProcessTimeTicksConverter::IsSkewAdditiveForMetrics() const {
  76   return numerator_ == 1 && denominator_ == 1;
  77 }
  78
  79 base::TimeDelta InterProcessTimeTicksConverter::GetSkewForMetrics() const {
  80   return base::TimeTicks::FromInternalValue(remote_lower_bound_) -
  81       base::TimeTicks::FromInternalValue(local_base_time_);
  82 }
  83
  84 }  // namespace content