Update to current webrtc library

This is from the upstream library commit id
3326535126e435f1ba647885ce43a8f0f3d317eb, corresponding to Chromium
88.0.4290.1.

webrtc/modules/audio_processing/ns/fast_math.cc

@@ -0,0 +1,84 @@
+/*
+ *  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 <math.h>
+#include <stdint.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 = 0.69314718056f;
+  return FastLog2f(x) * kLogOf2;
+}
+
+void LogApproximation(rtc::ArrayView<const float> x, rtc::ArrayView<float> y) {
+  for (size_t k = 0; k < x.size(); ++k) {
+    y[k] = LogApproximation(x[k]);
+  }
+}
+
+float ExpApproximation(float x) {
+  constexpr float kLog10Ofe = 0.4342944819f;
+  return PowApproximation(10.f, x * kLog10Ofe);
+}
+
+void ExpApproximation(rtc::ArrayView<const float> x, rtc::ArrayView<float> y) {
+  for (size_t k = 0; k < x.size(); ++k) {
+    y[k] = ExpApproximation(x[k]);
+  }
+}
+
+void ExpApproximationSignFlip(rtc::ArrayView<const float> x,
+                              rtc::ArrayView<float> y) {
+  for (size_t k = 0; k < x.size(); ++k) {
+    y[k] = ExpApproximation(-x[k]);
+  }
+}
+
+}  // namespace webrtc