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1 /*
2  *  Copyright (c) 2013 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 // Modified from the Chromium original:
12 // src/media/base/sinc_resampler.cc
13 
14 // Initial input buffer layout, dividing into regions r0_ to r4_ (note: r0_, r3_
15 // and r4_ will move after the first load):
16 //
17 // |----------------|-----------------------------------------|----------------|
18 //
19 //                                        request_frames_
20 //                   <--------------------------------------------------------->
21 //                                    r0_ (during first load)
22 //
23 //  kKernelSize / 2   kKernelSize / 2         kKernelSize / 2   kKernelSize / 2
24 // <---------------> <--------------->       <---------------> <--------------->
25 //        r1_               r2_                     r3_               r4_
26 //
27 //                             block_size_ == r4_ - r2_
28 //                   <--------------------------------------->
29 //
30 //                                                  request_frames_
31 //                                    <------------------ ... ----------------->
32 //                                               r0_ (during second load)
33 //
34 // On the second request r0_ slides to the right by kKernelSize / 2 and r3_, r4_
35 // and block_size_ are reinitialized via step (3) in the algorithm below.
36 //
37 // These new regions remain constant until a Flush() occurs.  While complicated,
38 // this allows us to reduce jitter by always requesting the same amount from the
39 // provided callback.
40 //
41 // The algorithm:
42 //
43 // 1) Allocate input_buffer of size: request_frames_ + kKernelSize; this ensures
44 //    there's enough room to read request_frames_ from the callback into region
45 //    r0_ (which will move between the first and subsequent passes).
46 //
47 // 2) Let r1_, r2_ each represent half the kernel centered around r0_:
48 //
49 //        r0_ = input_buffer_ + kKernelSize / 2
50 //        r1_ = input_buffer_
51 //        r2_ = r0_
52 //
53 //    r0_ is always request_frames_ in size.  r1_, r2_ are kKernelSize / 2 in
54 //    size.  r1_ must be zero initialized to avoid convolution with garbage (see
55 //    step (5) for why).
56 //
57 // 3) Let r3_, r4_ each represent half the kernel right aligned with the end of
58 //    r0_ and choose block_size_ as the distance in frames between r4_ and r2_:
59 //
60 //        r3_ = r0_ + request_frames_ - kKernelSize
61 //        r4_ = r0_ + request_frames_ - kKernelSize / 2
62 //        block_size_ = r4_ - r2_ = request_frames_ - kKernelSize / 2
63 //
64 // 4) Consume request_frames_ frames into r0_.
65 //
66 // 5) Position kernel centered at start of r2_ and generate output frames until
67 //    the kernel is centered at the start of r4_ or we've finished generating
68 //    all the output frames.
69 //
70 // 6) Wrap left over data from the r3_ to r1_ and r4_ to r2_.
71 //
72 // 7) If we're on the second load, in order to avoid overwriting the frames we
73 //    just wrapped from r4_ we need to slide r0_ to the right by the size of
74 //    r4_, which is kKernelSize / 2:
75 //
76 //        r0_ = r0_ + kKernelSize / 2 = input_buffer_ + kKernelSize
77 //
78 //    r3_, r4_, and block_size_ then need to be reinitialized, so goto (3).
79 //
80 // 8) Else, if we're not on the second load, goto (4).
81 //
82 // Note: we're glossing over how the sub-sample handling works with
83 // |virtual_source_idx_|, etc.
84 
85 // MSVC++ requires this to be set before any other includes to get M_PI.
86 #define _USE_MATH_DEFINES
87 
88 #include "webrtc/common_audio/resampler/sinc_resampler.h"
89 #include "webrtc/system_wrappers/interface/compile_assert.h"
90 #include "webrtc/system_wrappers/interface/cpu_features_wrapper.h"
91 #include "webrtc/typedefs.h"
92 
93 #include <assert.h>
94 #include <math.h>
95 #include <string.h>
96 
97 #include <limits>
98 
99 namespace webrtc {
100 
SincScaleFactor(double io_ratio)101 static double SincScaleFactor(double io_ratio) {
102   // |sinc_scale_factor| is basically the normalized cutoff frequency of the
103   // low-pass filter.
104   double sinc_scale_factor = io_ratio > 1.0 ? 1.0 / io_ratio : 1.0;
105 
106   // The sinc function is an idealized brick-wall filter, but since we're
107   // windowing it the transition from pass to stop does not happen right away.
108   // So we should adjust the low pass filter cutoff slightly downward to avoid
109   // some aliasing at the very high-end.
110   // TODO(crogers): this value is empirical and to be more exact should vary
111   // depending on kKernelSize.
112   sinc_scale_factor *= 0.9;
113 
114   return sinc_scale_factor;
115 }
116 
117 // If we know the minimum architecture at compile time, avoid CPU detection.
118 #if defined(WEBRTC_ARCH_X86_FAMILY)
119 #if defined(__SSE2__)
120 #define CONVOLVE_FUNC Convolve_SSE
InitializeCPUSpecificFeatures()121 void SincResampler::InitializeCPUSpecificFeatures() {}
122 #else
123 // x86 CPU detection required.  Function will be set by
124 // InitializeCPUSpecificFeatures().
125 // TODO(dalecurtis): Once Chrome moves to an SSE baseline this can be removed.
126 #define CONVOLVE_FUNC convolve_proc_
127 
InitializeCPUSpecificFeatures()128 void SincResampler::InitializeCPUSpecificFeatures() {
129   convolve_proc_ = WebRtc_GetCPUInfo(kSSE2) ? Convolve_SSE : Convolve_C;
130 }
131 #endif
132 #elif defined(WEBRTC_ARCH_ARM_V7)
133 #if defined(WEBRTC_ARCH_ARM_NEON)
134 #define CONVOLVE_FUNC Convolve_NEON
InitializeCPUSpecificFeatures()135 void SincResampler::InitializeCPUSpecificFeatures() {}
136 #else
137 // ARM CPU detection required.  Function will be set by
138 // InitializeCPUSpecificFeatures().
139 #define CONVOLVE_FUNC convolve_proc_
140 
InitializeCPUSpecificFeatures()141 void SincResampler::InitializeCPUSpecificFeatures() {
142   convolve_proc_ = WebRtc_GetCPUFeaturesARM() & kCPUFeatureNEON ?
143       Convolve_NEON : Convolve_C;
144 }
145 #endif
146 #else
147 // Unknown architecture.
148 #define CONVOLVE_FUNC Convolve_C
InitializeCPUSpecificFeatures()149 void SincResampler::InitializeCPUSpecificFeatures() {}
150 #endif
151 
SincResampler(double io_sample_rate_ratio,int request_frames,SincResamplerCallback * read_cb)152 SincResampler::SincResampler(double io_sample_rate_ratio,
153                              int request_frames,
154                              SincResamplerCallback* read_cb)
155     : io_sample_rate_ratio_(io_sample_rate_ratio),
156       read_cb_(read_cb),
157       request_frames_(request_frames),
158       input_buffer_size_(request_frames_ + kKernelSize),
159       // Create input buffers with a 16-byte alignment for SSE optimizations.
160       kernel_storage_(static_cast<float*>(
161           AlignedMalloc(sizeof(float) * kKernelStorageSize, 16))),
162       kernel_pre_sinc_storage_(static_cast<float*>(
163           AlignedMalloc(sizeof(float) * kKernelStorageSize, 16))),
164       kernel_window_storage_(static_cast<float*>(
165           AlignedMalloc(sizeof(float) * kKernelStorageSize, 16))),
166       input_buffer_(static_cast<float*>(
167           AlignedMalloc(sizeof(float) * input_buffer_size_, 16))),
168 #if defined(WEBRTC_CPU_DETECTION)
169       convolve_proc_(NULL),
170 #endif
171       r1_(input_buffer_.get()),
172       r2_(input_buffer_.get() + kKernelSize / 2) {
173 #if defined(WEBRTC_CPU_DETECTION)
174   InitializeCPUSpecificFeatures();
175   assert(convolve_proc_);
176 #endif
177   assert(request_frames_ > 0);
178   Flush();
179   assert(block_size_ > kKernelSize);
180 
181   memset(kernel_storage_.get(), 0,
182          sizeof(*kernel_storage_.get()) * kKernelStorageSize);
183   memset(kernel_pre_sinc_storage_.get(), 0,
184          sizeof(*kernel_pre_sinc_storage_.get()) * kKernelStorageSize);
185   memset(kernel_window_storage_.get(), 0,
186          sizeof(*kernel_window_storage_.get()) * kKernelStorageSize);
187 
188   InitializeKernel();
189 }
190 
~SincResampler()191 SincResampler::~SincResampler() {}
192 
UpdateRegions(bool second_load)193 void SincResampler::UpdateRegions(bool second_load) {
194   // Setup various region pointers in the buffer (see diagram above).  If we're
195   // on the second load we need to slide r0_ to the right by kKernelSize / 2.
196   r0_ = input_buffer_.get() + (second_load ? kKernelSize : kKernelSize / 2);
197   r3_ = r0_ + request_frames_ - kKernelSize;
198   r4_ = r0_ + request_frames_ - kKernelSize / 2;
199   block_size_ = r4_ - r2_;
200 
201   // r1_ at the beginning of the buffer.
202   assert(r1_ == input_buffer_.get());
203   // r1_ left of r2_, r4_ left of r3_ and size correct.
204   assert(r2_ - r1_ == r4_ - r3_);
205   // r2_ left of r3.
206   assert(r2_ < r3_);
207 }
208 
InitializeKernel()209 void SincResampler::InitializeKernel() {
210   // Blackman window parameters.
211   static const double kAlpha = 0.16;
212   static const double kA0 = 0.5 * (1.0 - kAlpha);
213   static const double kA1 = 0.5;
214   static const double kA2 = 0.5 * kAlpha;
215 
216   // Generates a set of windowed sinc() kernels.
217   // We generate a range of sub-sample offsets from 0.0 to 1.0.
218   const double sinc_scale_factor = SincScaleFactor(io_sample_rate_ratio_);
219   for (int offset_idx = 0; offset_idx <= kKernelOffsetCount; ++offset_idx) {
220     const float subsample_offset =
221         static_cast<float>(offset_idx) / kKernelOffsetCount;
222 
223     for (int i = 0; i < kKernelSize; ++i) {
224       const int idx = i + offset_idx * kKernelSize;
225       const float pre_sinc =
226           static_cast<float>(M_PI * (i - kKernelSize / 2 - subsample_offset));
227       kernel_pre_sinc_storage_[idx] = pre_sinc;
228 
229       // Compute Blackman window, matching the offset of the sinc().
230       const float x = (i - subsample_offset) / kKernelSize;
231       const float window = static_cast<float>(kA0 - kA1 * cos(2.0 * M_PI * x) +
232           kA2 * cos(4.0 * M_PI * x));
233       kernel_window_storage_[idx] = window;
234 
235       // Compute the sinc with offset, then window the sinc() function and store
236       // at the correct offset.
237       kernel_storage_[idx] = static_cast<float>(window *
238           ((pre_sinc == 0) ?
239               sinc_scale_factor :
240               (sin(sinc_scale_factor * pre_sinc) / pre_sinc)));
241     }
242   }
243 }
244 
SetRatio(double io_sample_rate_ratio)245 void SincResampler::SetRatio(double io_sample_rate_ratio) {
246   if (fabs(io_sample_rate_ratio_ - io_sample_rate_ratio) <
247       std::numeric_limits<double>::epsilon()) {
248     return;
249   }
250 
251   io_sample_rate_ratio_ = io_sample_rate_ratio;
252 
253   // Optimize reinitialization by reusing values which are independent of
254   // |sinc_scale_factor|.  Provides a 3x speedup.
255   const double sinc_scale_factor = SincScaleFactor(io_sample_rate_ratio_);
256   for (int offset_idx = 0; offset_idx <= kKernelOffsetCount; ++offset_idx) {
257     for (int i = 0; i < kKernelSize; ++i) {
258       const int idx = i + offset_idx * kKernelSize;
259       const float window = kernel_window_storage_[idx];
260       const float pre_sinc = kernel_pre_sinc_storage_[idx];
261 
262       kernel_storage_[idx] = static_cast<float>(window *
263           ((pre_sinc == 0) ?
264               sinc_scale_factor :
265               (sin(sinc_scale_factor * pre_sinc) / pre_sinc)));
266     }
267   }
268 }
269 
Resample(int frames,float * destination)270 void SincResampler::Resample(int frames, float* destination) {
271   int remaining_frames = frames;
272 
273   // Step (1) -- Prime the input buffer at the start of the input stream.
274   if (!buffer_primed_ && remaining_frames) {
275     read_cb_->Run(request_frames_, r0_);
276     buffer_primed_ = true;
277   }
278 
279   // Step (2) -- Resample!  const what we can outside of the loop for speed.  It
280   // actually has an impact on ARM performance.  See inner loop comment below.
281   const double current_io_ratio = io_sample_rate_ratio_;
282   const float* const kernel_ptr = kernel_storage_.get();
283   while (remaining_frames) {
284     // |i| may be negative if the last Resample() call ended on an iteration
285     // that put |virtual_source_idx_| over the limit.
286     //
287     // Note: The loop construct here can severely impact performance on ARM
288     // or when built with clang.  See https://codereview.chromium.org/18566009/
289     for (int i = static_cast<int>(
290              ceil((block_size_ - virtual_source_idx_) / current_io_ratio));
291          i > 0; --i) {
292       assert(virtual_source_idx_ < block_size_);
293 
294       // |virtual_source_idx_| lies in between two kernel offsets so figure out
295       // what they are.
296       const int source_idx = static_cast<int>(virtual_source_idx_);
297       const double subsample_remainder = virtual_source_idx_ - source_idx;
298 
299       const double virtual_offset_idx =
300           subsample_remainder * kKernelOffsetCount;
301       const int offset_idx = static_cast<int>(virtual_offset_idx);
302 
303       // We'll compute "convolutions" for the two kernels which straddle
304       // |virtual_source_idx_|.
305       const float* const k1 = kernel_ptr + offset_idx * kKernelSize;
306       const float* const k2 = k1 + kKernelSize;
307 
308       // Ensure |k1|, |k2| are 16-byte aligned for SIMD usage.  Should always be
309       // true so long as kKernelSize is a multiple of 16.
310       assert(0u == (reinterpret_cast<uintptr_t>(k1) & 0x0F));
311       assert(0u == (reinterpret_cast<uintptr_t>(k2) & 0x0F));
312 
313       // Initialize input pointer based on quantized |virtual_source_idx_|.
314       const float* const input_ptr = r1_ + source_idx;
315 
316       // Figure out how much to weight each kernel's "convolution".
317       const double kernel_interpolation_factor =
318           virtual_offset_idx - offset_idx;
319       *destination++ = CONVOLVE_FUNC(
320           input_ptr, k1, k2, kernel_interpolation_factor);
321 
322       // Advance the virtual index.
323       virtual_source_idx_ += current_io_ratio;
324 
325       if (!--remaining_frames)
326         return;
327     }
328 
329     // Wrap back around to the start.
330     virtual_source_idx_ -= block_size_;
331 
332     // Step (3) -- Copy r3_, r4_ to r1_, r2_.
333     // This wraps the last input frames back to the start of the buffer.
334     memcpy(r1_, r3_, sizeof(*input_buffer_.get()) * kKernelSize);
335 
336     // Step (4) -- Reinitialize regions if necessary.
337     if (r0_ == r2_)
338       UpdateRegions(true);
339 
340     // Step (5) -- Refresh the buffer with more input.
341     read_cb_->Run(request_frames_, r0_);
342   }
343 }
344 
345 #undef CONVOLVE_FUNC
346 
ChunkSize() const347 int SincResampler::ChunkSize() const {
348   return static_cast<int>(block_size_ / io_sample_rate_ratio_);
349 }
350 
Flush()351 void SincResampler::Flush() {
352   virtual_source_idx_ = 0;
353   buffer_primed_ = false;
354   memset(input_buffer_.get(), 0,
355          sizeof(*input_buffer_.get()) * input_buffer_size_);
356   UpdateRegions(false);
357 }
358 
Convolve_C(const float * input_ptr,const float * k1,const float * k2,double kernel_interpolation_factor)359 float SincResampler::Convolve_C(const float* input_ptr, const float* k1,
360                                 const float* k2,
361                                 double kernel_interpolation_factor) {
362   float sum1 = 0;
363   float sum2 = 0;
364 
365   // Generate a single output sample.  Unrolling this loop hurt performance in
366   // local testing.
367   int n = kKernelSize;
368   while (n--) {
369     sum1 += *input_ptr * *k1++;
370     sum2 += *input_ptr++ * *k2++;
371   }
372 
373   // Linearly interpolate the two "convolutions".
374   return static_cast<float>((1.0 - kernel_interpolation_factor) * sum1 +
375       kernel_interpolation_factor * sum2);
376 }
377 
378 }  // namespace webrtc
379