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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/optimization_guide/core/noisy_metrics_recorder.h"
#include <cmath>
#include "base/check_op.h"
#include "base/logging.h"
#include "base/rand_util.h"
NoisyMetricsRecorder::NoisyMetricsRecorder() = default;
NoisyMetricsRecorder::~NoisyMetricsRecorder() = default;
uint32_t NoisyMetricsRecorder::GetNoisyMetric(float flip_probability,
uint32_t original_metric,
uint8_t count_bits) {
DCHECK_LE(flip_probability, 1.0f);
DCHECK_GE(flip_probability, 0.0f);
// |original_metric| should fit within least significant |count_bits|.
DCHECK_LE(original_metric, std::pow(2, count_bits) - 1);
uint32_t flipped_value = 0u;
for (size_t idx = 0; idx < count_bits; ++idx) {
uint32_t flipped_bit = 0;
uint32_t bit = original_metric & 0x1;
original_metric = original_metric >> 1;
float first_coin_flip = GetRandBetween0And1();
if (first_coin_flip < flip_probability) {
flipped_bit = GetRandEither0Or1();
} else {
flipped_bit = bit;
}
flipped_value |= (flipped_bit << idx);
}
// The method has iterated through least significant |count_bits| and did that
// many right shifts. At this point, rest of the bits in |original_metric|
// should be 0.
DCHECK_EQ(original_metric, 0u);
DCHECK_EQ(flipped_value >> count_bits, 0u);
return flipped_value;
}
float NoisyMetricsRecorder::GetRandBetween0And1() const {
return base::RandDouble();
}
int NoisyMetricsRecorder::GetRandEither0Or1() const {
return base::RandInt(0, 1);
}
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