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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.
#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_TIMING_TIME_CLAMPER_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_TIMING_TIME_CLAMPER_H_
#include "base/macros.h"
#include "build/build_config.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include <stdint.h>
namespace blink {
class CORE_EXPORT TimeClamper {
USING_FAST_MALLOC(TimeClamper);
public:
// As site isolation is enabled on desktop platforms, we can safely provide
// more timing resolution. Jittering is still enabled everywhere.
#if defined(OS_ANDROID)
static constexpr double kResolutionSeconds = 100e-6;
#else
static constexpr double kResolutionSeconds = 5e-6;
#endif
TimeClamper();
// Deterministically clamp the time value |time_seconds| to a fixed interval
// to prevent timing attacks. See
// http://www.w3.org/TR/hr-time-2/#privacy-security.
//
// For each clamped time interval, we compute a pseudorandom transition
// threshold. The returned time will either be the start of that interval or
// the next one depending on which side of the threshold |time_seconds| is.
double ClampTimeResolution(double time_seconds) const;
private:
inline double ThresholdFor(double clamped_time) const;
static inline double ToDouble(uint64_t value);
static inline uint64_t MurmurHash3(uint64_t value);
uint64_t secret_;
DISALLOW_COPY_AND_ASSIGN(TimeClamper);
};
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_CORE_TIMING_TIME_CLAMPER_H_
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