1/*
2 *  Copyright (c) 2012 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 "webrtc/common_audio/signal_processing/include/real_fft.h"
12
13#include <stdlib.h>
14
15#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
16
17struct RealFFT {
18  int order;
19};
20
21struct RealFFT* WebRtcSpl_CreateRealFFTC(int order) {
22  struct RealFFT* self = NULL;
23
24  if (order > kMaxFFTOrder || order < 0) {
25    return NULL;
26  }
27
28  self = malloc(sizeof(struct RealFFT));
29  if (self == NULL) {
30    return NULL;
31  }
32  self->order = order;
33
34  return self;
35}
36
37void WebRtcSpl_FreeRealFFTC(struct RealFFT* self) {
38  if (self != NULL) {
39    free(self);
40  }
41}
42
43// The C version FFT functions (i.e. WebRtcSpl_RealForwardFFTC and
44// WebRtcSpl_RealInverseFFTC) are real-valued FFT wrappers for complex-valued
45// FFT implementation in SPL.
46
47int WebRtcSpl_RealForwardFFTC(struct RealFFT* self,
48                              const int16_t* real_data_in,
49                              int16_t* complex_data_out) {
50  int i = 0;
51  int j = 0;
52  int result = 0;
53  int n = 1 << self->order;
54  // The complex-value FFT implementation needs a buffer to hold 2^order
55  // 16-bit COMPLEX numbers, for both time and frequency data.
56  int16_t complex_buffer[2 << kMaxFFTOrder];
57
58  // Insert zeros to the imaginary parts for complex forward FFT input.
59  for (i = 0, j = 0; i < n; i += 1, j += 2) {
60    complex_buffer[j] = real_data_in[i];
61    complex_buffer[j + 1] = 0;
62  };
63
64  WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
65  result = WebRtcSpl_ComplexFFT(complex_buffer, self->order, 1);
66
67  // For real FFT output, use only the first N + 2 elements from
68  // complex forward FFT.
69  memcpy(complex_data_out, complex_buffer, sizeof(int16_t) * (n + 2));
70
71  return result;
72}
73
74int WebRtcSpl_RealInverseFFTC(struct RealFFT* self,
75                              const int16_t* complex_data_in,
76                              int16_t* real_data_out) {
77  int i = 0;
78  int j = 0;
79  int result = 0;
80  int n = 1 << self->order;
81  // Create the buffer specific to complex-valued FFT implementation.
82  int16_t complex_buffer[2 << kMaxFFTOrder];
83
84  // For n-point FFT, first copy the first n + 2 elements into complex
85  // FFT, then construct the remaining n - 2 elements by real FFT's
86  // conjugate-symmetric properties.
87  memcpy(complex_buffer, complex_data_in, sizeof(int16_t) * (n + 2));
88  for (i = n + 2; i < 2 * n; i += 2) {
89    complex_buffer[i] = complex_data_in[2 * n - i];
90    complex_buffer[i + 1] = -complex_data_in[2 * n - i + 1];
91  }
92
93  WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
94  result = WebRtcSpl_ComplexIFFT(complex_buffer, self->order, 1);
95
96  // Strip out the imaginary parts of the complex inverse FFT output.
97  for (i = 0, j = 0; i < n; i += 1, j += 2) {
98    real_data_out[i] = complex_buffer[j];
99  }
100
101  return result;
102}
103
104#if defined(WEBRTC_DETECT_ARM_NEON) || defined(WEBRTC_ARCH_ARM_NEON)
105// TODO(kma): Replace the following function bodies into optimized functions
106// for ARM Neon.
107struct RealFFT* WebRtcSpl_CreateRealFFTNeon(int order) {
108  return WebRtcSpl_CreateRealFFTC(order);
109}
110
111void WebRtcSpl_FreeRealFFTNeon(struct RealFFT* self) {
112  WebRtcSpl_FreeRealFFTC(self);
113}
114
115int WebRtcSpl_RealForwardFFTNeon(struct RealFFT* self,
116                                 const int16_t* real_data_in,
117                                 int16_t* complex_data_out) {
118  return WebRtcSpl_RealForwardFFTC(self, real_data_in, complex_data_out);
119}
120
121int WebRtcSpl_RealInverseFFTNeon(struct RealFFT* self,
122                                 const int16_t* complex_data_in,
123                                 int16_t* real_data_out) {
124  return WebRtcSpl_RealInverseFFTC(self, complex_data_in, real_data_out);
125}
126#endif  // WEBRTC_DETECT_ARM_NEON || WEBRTC_ARCH_ARM_NEON
127