1 /*
2 * Copyright (c) 2014 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 "common_audio/fir_filter_c.h"
12
13 #include <string.h>
14
15 #include <memory>
16
17 #include "rtc_base/checks.h"
18
19 namespace webrtc {
20
~FIRFilterC()21 FIRFilterC::~FIRFilterC() {}
22
FIRFilterC(const float * coefficients,size_t coefficients_length)23 FIRFilterC::FIRFilterC(const float* coefficients, size_t coefficients_length)
24 : coefficients_length_(coefficients_length),
25 state_length_(coefficients_length - 1),
26 coefficients_(new float[coefficients_length_]),
27 state_(new float[state_length_]) {
28 for (size_t i = 0; i < coefficients_length_; ++i) {
29 coefficients_[i] = coefficients[coefficients_length_ - i - 1];
30 }
31 memset(state_.get(), 0, state_length_ * sizeof(state_[0]));
32 }
33
Filter(const float * in,size_t length,float * out)34 void FIRFilterC::Filter(const float* in, size_t length, float* out) {
35 RTC_DCHECK_GT(length, 0);
36
37 // Convolves the input signal `in` with the filter kernel `coefficients_`
38 // taking into account the previous state.
39 for (size_t i = 0; i < length; ++i) {
40 out[i] = 0.f;
41 size_t j;
42 for (j = 0; state_length_ > i && j < state_length_ - i; ++j) {
43 out[i] += state_[i + j] * coefficients_[j];
44 }
45 for (; j < coefficients_length_; ++j) {
46 out[i] += in[j + i - state_length_] * coefficients_[j];
47 }
48 }
49
50 // Update current state.
51 if (length >= state_length_) {
52 memcpy(state_.get(), &in[length - state_length_],
53 state_length_ * sizeof(*in));
54 } else {
55 memmove(state_.get(), &state_[length],
56 (state_length_ - length) * sizeof(state_[0]));
57 memcpy(&state_[state_length_ - length], in, length * sizeof(*in));
58 }
59 }
60
61 } // namespace webrtc
62