common_audio/resampler/sinc_resampler.cc

/*
 *  Copyright (c) 2013 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.
 */

// Modified from the Chromium original:
// src/media/base/sinc_resampler.cc

// Initial input buffer layout, dividing into regions r0_ to r4_ (note: r0_, r3_
// and r4_ will move after the first load):
//
// |----------------|-----------------------------------------|----------------|
//
//                                        request_frames_
//                   <--------------------------------------------------------->
//                                    r0_ (during first load)
//
//  kKernelSize / 2   kKernelSize / 2         kKernelSize / 2   kKernelSize / 2
// <---------------> <--------------->       <---------------> <--------------->
//        r1_               r2_                     r3_               r4_
//
//                             block_size_ == r4_ - r2_
//                   <--------------------------------------->
//
//                                                  request_frames_
//                                    <------------------ ... ----------------->
//                                               r0_ (during second load)
//
// On the second request r0_ slides to the right by kKernelSize / 2 and r3_, r4_
// and block_size_ are reinitialized via step (3) in the algorithm below.
//
// These new regions remain constant until a Flush() occurs.  While complicated,
// this allows us to reduce jitter by always requesting the same amount from the
// provided callback.
//
// The algorithm:
//
// 1) Allocate input_buffer of size: request_frames_ + kKernelSize; this ensures
//    there's enough room to read request_frames_ from the callback into region
//    r0_ (which will move between the first and subsequent passes).
//
// 2) Let r1_, r2_ each represent half the kernel centered around r0_:
//
//        r0_ = input_buffer_ + kKernelSize / 2
//        r1_ = input_buffer_
//        r2_ = r0_
//
//    r0_ is always request_frames_ in size.  r1_, r2_ are kKernelSize / 2 in
//    size.  r1_ must be zero initialized to avoid convolution with garbage (see
//    step (5) for why).
//
// 3) Let r3_, r4_ each represent half the kernel right aligned with the end of
//    r0_ and choose block_size_ as the distance in frames between r4_ and r2_:
//
//        r3_ = r0_ + request_frames_ - kKernelSize
//        r4_ = r0_ + request_frames_ - kKernelSize / 2
//        block_size_ = r4_ - r2_ = request_frames_ - kKernelSize / 2
//
// 4) Consume request_frames_ frames into r0_.
//
// 5) Position kernel centered at start of r2_ and generate output frames until
//    the kernel is centered at the start of r4_ or we've finished generating
//    all the output frames.
//
// 6) Wrap left over data from the r3_ to r1_ and r4_ to r2_.
//
// 7) If we're on the second load, in order to avoid overwriting the frames we
//    just wrapped from r4_ we need to slide r0_ to the right by the size of
//    r4_, which is kKernelSize / 2:
//
//        r0_ = r0_ + kKernelSize / 2 = input_buffer_ + kKernelSize
//
//    r3_, r4_, and block_size_ then need to be reinitialized, so goto (3).
//
// 8) Else, if we're not on the second load, goto (4).
//
// Note: we're glossing over how the sub-sample handling works with
// `virtual_source_idx_`, etc.

// MSVC++ requires this to be set before any other includes to get M_PI.
#define _USE_MATH_DEFINES

#include "common_audio/resampler/sinc_resampler.h"

#include <math.h>
#include <stdint.h>
#include <string.h>

#include <limits>

#include "rtc_base/checks.h"
#include "rtc_base/system/arch.h"
#include "system_wrappers/include/cpu_features_wrapper.h"  // kSSE2, WebRtc_G...

namespace webrtc {

namespace {

double SincScaleFactor(double io_ratio) {
  // `sinc_scale_factor` is basically the normalized cutoff frequency of the
  // low-pass filter.
  double sinc_scale_factor = io_ratio > 1.0 ? 1.0 / io_ratio : 1.0;

  // The sinc function is an idealized brick-wall filter, but since we're
  // windowing it the transition from pass to stop does not happen right away.
  // So we should adjust the low pass filter cutoff slightly downward to avoid
  // some aliasing at the very high-end.
  // TODO(crogers): this value is empirical and to be more exact should vary
  // depending on kKernelSize.
  sinc_scale_factor *= 0.9;

  return sinc_scale_factor;
}

}  // namespace

const size_t SincResampler::kKernelSize;

// If we know the minimum architecture at compile time, avoid CPU detection.
void SincResampler::InitializeCPUSpecificFeatures() {
#if defined(WEBRTC_HAS_NEON)
  convolve_proc_ = Convolve_NEON;
#elif defined(WEBRTC_ARCH_X86_FAMILY)
  // Using AVX2 instead of SSE2 when AVX2/FMA3 supported.
  if (GetCPUInfo(kAVX2) && GetCPUInfo(kFMA3))
    convolve_proc_ = Convolve_AVX2;
  else if (GetCPUInfo(kSSE2))
    convolve_proc_ = Convolve_SSE;
  else
    convolve_proc_ = Convolve_C;
#else
  // Unknown architecture.
  convolve_proc_ = Convolve_C;
#endif
}

SincResampler::SincResampler(double io_sample_rate_ratio,
                             size_t request_frames,
                             SincResamplerCallback* read_cb)
    : io_sample_rate_ratio_(io_sample_rate_ratio),
      read_cb_(read_cb),
      request_frames_(request_frames),
      input_buffer_size_(request_frames_ + kKernelSize),
      // Create input buffers with a 32-byte alignment for SIMD optimizations.
      kernel_storage_(static_cast<float*>(
          AlignedMalloc(sizeof(float) * kKernelStorageSize, 32))),
      kernel_pre_sinc_storage_(static_cast<float*>(
          AlignedMalloc(sizeof(float) * kKernelStorageSize, 32))),
      kernel_window_storage_(static_cast<float*>(
          AlignedMalloc(sizeof(float) * kKernelStorageSize, 32))),
      input_buffer_(static_cast<float*>(
          AlignedMalloc(sizeof(float) * input_buffer_size_, 32))),
      convolve_proc_(nullptr),
      r1_(input_buffer_.get()),
      r2_(input_buffer_.get() + kKernelSize / 2) {
  InitializeCPUSpecificFeatures();
  RTC_DCHECK(convolve_proc_);
  RTC_DCHECK_GT(request_frames_, 0);
  Flush();
  RTC_DCHECK_GT(block_size_, kKernelSize);

  memset(kernel_storage_.get(), 0,
         sizeof(*kernel_storage_.get()) * kKernelStorageSize);
  memset(kernel_pre_sinc_storage_.get(), 0,
         sizeof(*kernel_pre_sinc_storage_.get()) * kKernelStorageSize);
  memset(kernel_window_storage_.get(), 0,
         sizeof(*kernel_window_storage_.get()) * kKernelStorageSize);

  InitializeKernel();
}

SincResampler::~SincResampler() {}

void SincResampler::UpdateRegions(bool second_load) {
  // Setup various region pointers in the buffer (see diagram above).  If we're
  // on the second load we need to slide r0_ to the right by kKernelSize / 2.
  r0_ = input_buffer_.get() + (second_load ? kKernelSize : kKernelSize / 2);
  r3_ = r0_ + request_frames_ - kKernelSize;
  r4_ = r0_ + request_frames_ - kKernelSize / 2;
  block_size_ = r4_ - r2_;

  // r1_ at the beginning of the buffer.
  RTC_DCHECK_EQ(r1_, input_buffer_.get());
  // r1_ left of r2_, r4_ left of r3_ and size correct.
  RTC_DCHECK_EQ(r2_ - r1_, r4_ - r3_);
  // r2_ left of r3.
  RTC_DCHECK_LT(r2_, r3_);
}

void SincResampler::InitializeKernel() {
  // Blackman window parameters.
  static const double kAlpha = 0.16;
  static const double kA0 = 0.5 * (1.0 - kAlpha);
  static const double kA1 = 0.5;
  static const double kA2 = 0.5 * kAlpha;

  // Generates a set of windowed sinc() kernels.
  // We generate a range of sub-sample offsets from 0.0 to 1.0.
  const double sinc_scale_factor = SincScaleFactor(io_sample_rate_ratio_);
  for (size_t offset_idx = 0; offset_idx <= kKernelOffsetCount; ++offset_idx) {
    const float subsample_offset =
        static_cast<float>(offset_idx) / kKernelOffsetCount;

    for (size_t i = 0; i < kKernelSize; ++i) {
      const size_t idx = i + offset_idx * kKernelSize;
      const float pre_sinc = static_cast<float>(
          M_PI * (static_cast<int>(i) - static_cast<int>(kKernelSize / 2) -
                  subsample_offset));
      kernel_pre_sinc_storage_[idx] = pre_sinc;

      // Compute Blackman window, matching the offset of the sinc().
      const float x = (i - subsample_offset) / kKernelSize;
      const float window = static_cast<float>(kA0 - kA1 * cos(2.0 * M_PI * x) +
                                              kA2 * cos(4.0 * M_PI * x));
      kernel_window_storage_[idx] = window;

      // Compute the sinc with offset, then window the sinc() function and store
      // at the correct offset.
      kernel_storage_[idx] = static_cast<float>(
          window * ((pre_sinc == 0)
                        ? sinc_scale_factor
                        : (sin(sinc_scale_factor * pre_sinc) / pre_sinc)));
    }
  }
}

void SincResampler::SetRatio(double io_sample_rate_ratio) {
  if (fabs(io_sample_rate_ratio_ - io_sample_rate_ratio) <
      std::numeric_limits<double>::epsilon()) {
    return;
  }

  io_sample_rate_ratio_ = io_sample_rate_ratio;

  // Optimize reinitialization by reusing values which are independent of
  // `sinc_scale_factor`.  Provides a 3x speedup.
  const double sinc_scale_factor = SincScaleFactor(io_sample_rate_ratio_);
  for (size_t offset_idx = 0; offset_idx <= kKernelOffsetCount; ++offset_idx) {
    for (size_t i = 0; i < kKernelSize; ++i) {
      const size_t idx = i + offset_idx * kKernelSize;
      const float window = kernel_window_storage_[idx];
      const float pre_sinc = kernel_pre_sinc_storage_[idx];

      kernel_storage_[idx] = static_cast<float>(
          window * ((pre_sinc == 0)
                        ? sinc_scale_factor
                        : (sin(sinc_scale_factor * pre_sinc) / pre_sinc)));
    }
  }
}

void SincResampler::Resample(size_t frames, float* destination) {
  size_t remaining_frames = frames;

  // Step (1) -- Prime the input buffer at the start of the input stream.
  if (!buffer_primed_ && remaining_frames) {
    read_cb_->Run(request_frames_, r0_);
    buffer_primed_ = true;
  }

  // Step (2) -- Resample!  const what we can outside of the loop for speed.  It
  // actually has an impact on ARM performance.  See inner loop comment below.
  const double current_io_ratio = io_sample_rate_ratio_;
  const float* const kernel_ptr = kernel_storage_.get();
  while (remaining_frames) {
    // `i` may be negative if the last Resample() call ended on an iteration
    // that put `virtual_source_idx_` over the limit.
    //
    // Note: The loop construct here can severely impact performance on ARM
    // or when built with clang.  See https://codereview.chromium.org/18566009/
    for (int i = static_cast<int>(
             ceil((block_size_ - virtual_source_idx_) / current_io_ratio));
         i > 0; --i) {
      RTC_DCHECK_LT(virtual_source_idx_, block_size_);

      // `virtual_source_idx_` lies in between two kernel offsets so figure out
      // what they are.
      const int source_idx = static_cast<int>(virtual_source_idx_);
      const double subsample_remainder = virtual_source_idx_ - source_idx;

      const double virtual_offset_idx =
          subsample_remainder * kKernelOffsetCount;
      const int offset_idx = static_cast<int>(virtual_offset_idx);

      // We'll compute "convolutions" for the two kernels which straddle
      // `virtual_source_idx_`.
      const float* const k1 = kernel_ptr + offset_idx * kKernelSize;
      const float* const k2 = k1 + kKernelSize;

      // Ensure `k1`, `k2` are 32-byte aligned for SIMD usage.  Should always be
      // true so long as kKernelSize is a multiple of 32.
      RTC_DCHECK_EQ(0, reinterpret_cast<uintptr_t>(k1) % 32);
      RTC_DCHECK_EQ(0, reinterpret_cast<uintptr_t>(k2) % 32);

      // Initialize input pointer based on quantized `virtual_source_idx_`.
      const float* const input_ptr = r1_ + source_idx;

      // Figure out how much to weight each kernel's "convolution".
      const double kernel_interpolation_factor =
          virtual_offset_idx - offset_idx;
      *destination++ =
          convolve_proc_(input_ptr, k1, k2, kernel_interpolation_factor);

      // Advance the virtual index.
      virtual_source_idx_ += current_io_ratio;

      if (!--remaining_frames)
        return;
    }

    // Wrap back around to the start.
    virtual_source_idx_ -= block_size_;

    // Step (3) -- Copy r3_, r4_ to r1_, r2_.
    // This wraps the last input frames back to the start of the buffer.
    memcpy(r1_, r3_, sizeof(*input_buffer_.get()) * kKernelSize);

    // Step (4) -- Reinitialize regions if necessary.
    if (r0_ == r2_)
      UpdateRegions(true);

    // Step (5) -- Refresh the buffer with more input.
    read_cb_->Run(request_frames_, r0_);
  }
}

#undef CONVOLVE_FUNC

size_t SincResampler::ChunkSize() const {
  return static_cast<size_t>(block_size_ / io_sample_rate_ratio_);
}

void SincResampler::Flush() {
  virtual_source_idx_ = 0;
  buffer_primed_ = false;
  memset(input_buffer_.get(), 0,
         sizeof(*input_buffer_.get()) * input_buffer_size_);
  UpdateRegions(false);
}

float SincResampler::Convolve_C(const float* input_ptr,
                                const float* k1,
                                const float* k2,
                                double kernel_interpolation_factor) {
  float sum1 = 0;
  float sum2 = 0;

  // Generate a single output sample.  Unrolling this loop hurt performance in
  // local testing.
  size_t n = kKernelSize;
  while (n--) {
    sum1 += *input_ptr * *k1++;
    sum2 += *input_ptr++ * *k2++;
  }

  // Linearly interpolate the two "convolutions".
  return static_cast<float>((1.0 - kernel_interpolation_factor) * sum1 +
                            kernel_interpolation_factor * sum2);
}

}  // namespace webrtc