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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/public/common/device_memory/approximated_device_memory.h"
#include "base/check_op.h"
#include "base/system/sys_info.h"
namespace blink {
// static
float ApproximatedDeviceMemory::approximated_device_memory_gb_ = 0.0;
int64_t ApproximatedDeviceMemory::physical_memory_mb_ = 0;
// static
void ApproximatedDeviceMemory::Initialize() {
if (approximated_device_memory_gb_ > 0.0)
return;
DCHECK_EQ(0, physical_memory_mb_);
physical_memory_mb_ = ::base::SysInfo::AmountOfPhysicalMemoryMB();
CalculateAndSetApproximatedDeviceMemory();
}
// static
float ApproximatedDeviceMemory::GetApproximatedDeviceMemory() {
return approximated_device_memory_gb_;
}
// static
void ApproximatedDeviceMemory::CalculateAndSetApproximatedDeviceMemory() {
// The calculations in this method are described in the specification:
// https://w3c.github.io/device-memory/.
DCHECK_GT(physical_memory_mb_, 0);
int lower_bound = physical_memory_mb_;
int power = 0;
// Extract the most-significant-bit and its location.
while (lower_bound > 1) {
lower_bound >>= 1;
power++;
}
// The remaining should always be equal to exactly 1.
DCHECK_EQ(lower_bound, 1);
int64_t upper_bound = lower_bound + 1;
lower_bound = lower_bound << power;
upper_bound = upper_bound << power;
// Find the closest bound, and convert it to GB.
if (physical_memory_mb_ - lower_bound <= upper_bound - physical_memory_mb_)
approximated_device_memory_gb_ = static_cast<float>(lower_bound) / 1024.0;
else
approximated_device_memory_gb_ = static_cast<float>(upper_bound) / 1024.0;
// Max-limit the reported value to 8GB to reduce fingerprintability of
// high-spec machines.
if (approximated_device_memory_gb_ > 8)
approximated_device_memory_gb_ = 8.0;
}
// static
void ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(
int64_t physical_memory_mb) {
physical_memory_mb_ = physical_memory_mb;
CalculateAndSetApproximatedDeviceMemory();
}
} // namespace blink
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