1 files changed, 61 insertions, 0 deletions
diff --git a/chromium/ui/latency/fixed_point.cc b/chromium/ui/latency/fixed_point.cc
new file mode 100644
index 00000000000..fafcf9ee85e
--- /dev/null
+++ b/chromium/ui/latency/fixed_point.cc
@@ -0,0 +1,61 @@
+// Copyright 2018 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/latency/fixed_point.h"
+
+#include <cmath>
+#include <limits>
+
+#include "base/logging.h"
+
+namespace ui {
+namespace frame_metrics {
+
+namespace {
+
+constexpr uint64_t k2Pow32{1ULL << 32};
+constexpr uint64_t k32LsbMask{0xFFFFFFFF};
+
+}  // namespace
+
+Accumulator96b::Accumulator96b(uint32_t value_to_square, uint32_t weight) {
+  uint64_t square = static_cast<uint64_t>(value_to_square) * value_to_square;
+  uint64_t ms64b_temp = (square >> 32) * weight;
+  uint64_t ls32b_temp = (square & k32LsbMask) * weight;
+  ms64b = ms64b_temp + (ls32b_temp >> 32);
+  ls32b = ls32b_temp & k32LsbMask;
+}
+
+void Accumulator96b::Add(const Accumulator96b& rhs) {
+  uint64_t ls32b_temp = static_cast<uint64_t>(ls32b) + rhs.ls32b;
+  DCHECK_LT((ls32b_temp >> 32),
+            std::numeric_limits<decltype(ms64b)>::max() - rhs.ms64b)
+      << "Accumulator96b overflow.";
+  uint64_t ms64b_add = rhs.ms64b + (ls32b_temp >> 32);
+  DCHECK_LT(ms64b_add, std::numeric_limits<decltype(ms64b)>::max() - ms64b)
+      << "Accumulator96b overflow.";
+  ms64b += ms64b_add;
+  ls32b = ls32b_temp & k32LsbMask;
+}
+
+void Accumulator96b::Subtract(const Accumulator96b& rhs) {
+  uint64_t ls32b_temp = ls32b;
+  if (ls32b < rhs.ls32b) {
+    // Borrow from ms64b to ls32b.
+    ms64b--;
+    ls32b_temp |= k2Pow32;
+  }
+  DCHECK_GE(ms64b, rhs.ms64b) << "Accumulator96b underflow.";
+  DCHECK_GE(ls32b_temp, static_cast<uint64_t>(rhs.ls32b))
+      << "Accumulator96b underflow.";
+  ms64b -= rhs.ms64b;
+  ls32b = ls32b_temp - rhs.ls32b;
+}
+
+double Accumulator96b::ToDouble() const {
+  return (static_cast<double>(ms64b) * k2Pow32) + ls32b;
+}
+
+}  // namespace frame_metrics
+}  // namespace ui