tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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fast_math.cc (2288B)

      1 /*
      2 *  Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
      3 *
      4 *  Use of this source code is governed by a BSD-style license
      5 *  that can be found in the LICENSE file in the root of the source
      6 *  tree. An additional intellectual property rights grant can be found
      7 *  in the file PATENTS.  All contributing project authors may
      8 *  be found in the AUTHORS file in the root of the source tree.
      9 */
     10 
     11 #include "modules/audio_processing/ns/fast_math.h"
     12 
     13 #include <cmath>
     14 #include <cstddef>
     15 #include <cstdint>
     16 #include <numbers>
     17 
     18 #include "api/array_view.h"
     19 #include "rtc_base/checks.h"
     20 
     21 namespace webrtc {
     22 
     23 namespace {
     24 
     25 float FastLog2f(float in) {
     26  RTC_DCHECK_GT(in, .0f);
     27  // Read and interpret float as uint32_t and then cast to float.
     28  // This is done to extract the exponent (bits 30 - 23).
     29  // "Right shift" of the exponent is then performed by multiplying
     30  // with the constant (1/2^23). Finally, we subtract a constant to
     31  // remove the bias (https://en.wikipedia.org/wiki/Exponent_bias).
     32  union {
     33    float dummy;
     34    uint32_t a;
     35  } x = {in};
     36  float out = x.a;
     37  out *= 1.1920929e-7f;  // 1/2^23
     38  out -= 126.942695f;    // Remove bias.
     39  return out;
     40 }
     41 
     42 }  // namespace
     43 
     44 float SqrtFastApproximation(float f) {
     45  // TODO(peah): Add fast approximate implementation.
     46  return sqrtf(f);
     47 }
     48 
     49 float Pow2Approximation(float p) {
     50  // TODO(peah): Add fast approximate implementation.
     51  return powf(2.f, p);
     52 }
     53 
     54 float PowApproximation(float x, float p) {
     55  return Pow2Approximation(p * FastLog2f(x));
     56 }
     57 
     58 float LogApproximation(float x) {
     59  constexpr float kLogOf2 = std::numbers::ln2_v<float>;
     60  return FastLog2f(x) * kLogOf2;
     61 }
     62 
     63 void LogApproximation(ArrayView<const float> x, ArrayView<float> y) {
     64  for (size_t k = 0; k < x.size(); ++k) {
     65    y[k] = LogApproximation(x[k]);
     66  }
     67 }
     68 
     69 float ExpApproximation(float x) {
     70  constexpr float kLog10Ofe = std::numbers::log10e_v<float>;
     71  return PowApproximation(10.f, x * kLog10Ofe);
     72 }
     73 
     74 void ExpApproximation(ArrayView<const float> x, ArrayView<float> y) {
     75  for (size_t k = 0; k < x.size(); ++k) {
     76    y[k] = ExpApproximation(x[k]);
     77  }
     78 }
     79 
     80 void ExpApproximationSignFlip(ArrayView<const float> x, ArrayView<float> y) {
     81  for (size_t k = 0; k < x.size(); ++k) {
     82    y[k] = ExpApproximation(-x[k]);
     83  }
     84 }
     85 
     86 }  // namespace webrtc