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 17 struct RealFFT { 18 int order; 19 }; 20 21 struct RealFFT* WebRtcSpl_CreateRealFFT(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 37 void WebRtcSpl_FreeRealFFT(struct RealFFT* self) { 38 if (self != NULL) { 39 free(self); 40 } 41 } 42 43 // The C version FFT functions (i.e. WebRtcSpl_RealForwardFFT and 44 // WebRtcSpl_RealInverseFFT) are real-valued FFT wrappers for complex-valued 45 // FFT implementation in SPL. 46 47 int WebRtcSpl_RealForwardFFT(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 74 int WebRtcSpl_RealInverseFFT(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
