Creating utility for converting TimeTicks to WebKit double and use it in the Chrome compositor.

webkit/renderer/compositor_bindings/webkit_time.cc

+// Copyright 2012 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 "webkit/renderer/compositor_bindings/webkit_time.h"
+
+#include <limits>
+
+#include "base/float_util.h"
+
+namespace webkit {
+
+base::TimeTicks FromWebKitTime(double monotonic_time) {
+  // Outside of 2**53 the conversion to/from double isn't presevative.
+
+  if (monotonic_time == 0 || base::IsNaN(monotonic_time))
+    return base::TimeTicks();  // Preserve 0 so we can tell it doesn't exist.
+
+  double d_microseconds =
+      monotonic_time * static_cast<double>(base::Time::kMicrosecondsPerSecond);
+
+  // Check double isn't too big for an int64
+  if (d_microseconds >= static_cast<double>(std::numeric_limits<int64>::max()))
+    return base::TimeTicks::FromInternalValue(
+        std::numeric_limits<int64>::max());
+  if (d_microseconds <= static_cast<double>(std::numeric_limits<int64>::min()))
+    return base::TimeTicks::FromInternalValue(
+        std::numeric_limits<int64>::min());
+
+  int64 i_microseconds = static_cast<int64>(d_microseconds);
+  int64 epoch_ticks_t0 = base::TimeTicks::UnixEpoch().ToInternalValue();
+
+  // Make sure the Epoch adjustment won't cause over/under flow.
+  if (epoch_ticks_t0 > 0 &&
+      i_microseconds >= std::numeric_limits<int64>::max() - epoch_ticks_t0)
+    return base::TimeTicks::FromInternalValue(
+        std::numeric_limits<int64>::max());
+  if (epoch_ticks_t0 < 0 &&
+      i_microseconds <= std::numeric_limits<int64>::min() - epoch_ticks_t0)
+    return base::TimeTicks::FromInternalValue(
+        std::numeric_limits<int64>::min());
+
+  return base::TimeTicks::FromInternalValue(i_microseconds + epoch_ticks_t0);
+}
+
+double ToWebKitTime(base::TimeTicks monotonic_time) {
+  if (monotonic_time.is_null())
+    return 0;  // Preserve 0 so we can tell it doesn't exist.
+
+  int64 ticks = monotonic_time.ToInternalValue();
+  if (ticks == std::numeric_limits<int64>::max())
+    return std::numeric_limits<double>::infinity();
+  if (ticks == std::numeric_limits<int64>::min())
+    return -std::numeric_limits<double>::infinity();
+
+  return (static_cast<double>(ticks -
+                              base::TimeTicks::UnixEpoch().ToInternalValue()) /
+          static_cast<double>(base::Time::kMicrosecondsPerSecond));
+}
+
+}  // namespace webkit