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/*
* Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "modules/audio_processing/ns/fast_math.h"
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <numbers>
#include "api/array_view.h"
#include "rtc_base/checks.h"
namespace webrtc {
namespace {
float FastLog2f(float in) {
RTC_DCHECK_GT(in, .0f);
// Read and interpret float as uint32_t and then cast to float.
// This is done to extract the exponent (bits 30 - 23).
// "Right shift" of the exponent is then performed by multiplying
// with the constant (1/2^23). Finally, we subtract a constant to
// remove the bias (https://en.wikipedia.org/wiki/Exponent_bias).
union {
float dummy;
uint32_t a;
} x = {in};
float out = x.a;
out *= 1.1920929e-7f; // 1/2^23
out -= 126.942695f; // Remove bias.
return out;
}
} // namespace
float SqrtFastApproximation(float f) {
// TODO(peah): Add fast approximate implementation.
return sqrtf(f);
}
float Pow2Approximation(float p) {
// TODO(peah): Add fast approximate implementation.
return powf(2.f, p);
}
float PowApproximation(float x, float p) {
return Pow2Approximation(p * FastLog2f(x));
}
float LogApproximation(float x) {
constexpr float kLogOf2 = std::numbers::ln2_v<float>;
return FastLog2f(x) * kLogOf2;
}
void LogApproximation(ArrayView<const float> x, ArrayView<float> y) {
for (size_t k = 0; k < x.size(); ++k) {
y[k] = LogApproximation(x[k]);
}
}
float ExpApproximation(float x) {
constexpr float kLog10Ofe = std::numbers::log10e_v<float>;
return PowApproximation(10.f, x * kLog10Ofe);
}
void ExpApproximation(ArrayView<const float> x, ArrayView<float> y) {
for (size_t k = 0; k < x.size(); ++k) {
y[k] = ExpApproximation(x[k]);
}
}
void ExpApproximationSignFlip(ArrayView<const float> x, ArrayView<float> y) {
for (size_t k = 0; k < x.size(); ++k) {
y[k] = ExpApproximation(-x[k]);
}
}
} // namespace webrtc
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