85 lines
2.2 KiB
C++
85 lines
2.2 KiB
C++
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/*
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* Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "modules/audio_processing/ns/fast_math.h"
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#include <math.h>
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#include <stdint.h>
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#include "rtc_base/checks.h"
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namespace webrtc {
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namespace {
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float FastLog2f(float in) {
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RTC_DCHECK_GT(in, .0f);
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// Read and interpret float as uint32_t and then cast to float.
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// This is done to extract the exponent (bits 30 - 23).
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// "Right shift" of the exponent is then performed by multiplying
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// with the constant (1/2^23). Finally, we subtract a constant to
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// remove the bias (https://en.wikipedia.org/wiki/Exponent_bias).
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union {
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float dummy;
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uint32_t a;
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} x = {in};
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float out = x.a;
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out *= 1.1920929e-7f; // 1/2^23
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out -= 126.942695f; // Remove bias.
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return out;
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}
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} // namespace
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float SqrtFastApproximation(float f) {
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// TODO(peah): Add fast approximate implementation.
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return sqrtf(f);
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}
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float Pow2Approximation(float p) {
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// TODO(peah): Add fast approximate implementation.
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return powf(2.f, p);
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}
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float PowApproximation(float x, float p) {
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return Pow2Approximation(p * FastLog2f(x));
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}
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float LogApproximation(float x) {
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constexpr float kLogOf2 = 0.69314718056f;
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return FastLog2f(x) * kLogOf2;
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}
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void LogApproximation(rtc::ArrayView<const float> x, rtc::ArrayView<float> y) {
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for (size_t k = 0; k < x.size(); ++k) {
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y[k] = LogApproximation(x[k]);
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}
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}
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float ExpApproximation(float x) {
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constexpr float kLog10Ofe = 0.4342944819f;
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return PowApproximation(10.f, x * kLog10Ofe);
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}
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void ExpApproximation(rtc::ArrayView<const float> x, rtc::ArrayView<float> y) {
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for (size_t k = 0; k < x.size(); ++k) {
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y[k] = ExpApproximation(x[k]);
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}
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}
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void ExpApproximationSignFlip(rtc::ArrayView<const float> x,
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rtc::ArrayView<float> y) {
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for (size_t k = 0; k < x.size(); ++k) {
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y[k] = ExpApproximation(-x[k]);
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}
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}
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} // namespace webrtc
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