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// 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
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