103 lines
3.1 KiB
C
103 lines
3.1 KiB
C
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/*
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* Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "common_audio/signal_processing/include/real_fft.h"
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#include <stdlib.h>
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#include "common_audio/signal_processing/include/signal_processing_library.h"
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struct RealFFT {
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int order;
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};
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struct RealFFT* WebRtcSpl_CreateRealFFT(int order) {
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struct RealFFT* self = NULL;
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if (order > kMaxFFTOrder || order < 0) {
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return NULL;
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}
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self = malloc(sizeof(struct RealFFT));
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if (self == NULL) {
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return NULL;
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}
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self->order = order;
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return self;
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}
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void WebRtcSpl_FreeRealFFT(struct RealFFT* self) {
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if (self != NULL) {
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free(self);
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}
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}
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// The C version FFT functions (i.e. WebRtcSpl_RealForwardFFT and
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// WebRtcSpl_RealInverseFFT) are real-valued FFT wrappers for complex-valued
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// FFT implementation in SPL.
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int WebRtcSpl_RealForwardFFT(struct RealFFT* self,
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const int16_t* real_data_in,
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int16_t* complex_data_out) {
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int i = 0;
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int j = 0;
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int result = 0;
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int n = 1 << self->order;
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// The complex-value FFT implementation needs a buffer to hold 2^order
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// 16-bit COMPLEX numbers, for both time and frequency data.
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int16_t complex_buffer[2 << kMaxFFTOrder];
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// Insert zeros to the imaginary parts for complex forward FFT input.
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for (i = 0, j = 0; i < n; i += 1, j += 2) {
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complex_buffer[j] = real_data_in[i];
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complex_buffer[j + 1] = 0;
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};
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WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
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result = WebRtcSpl_ComplexFFT(complex_buffer, self->order, 1);
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// For real FFT output, use only the first N + 2 elements from
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// complex forward FFT.
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memcpy(complex_data_out, complex_buffer, sizeof(int16_t) * (n + 2));
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return result;
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}
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int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
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const int16_t* complex_data_in,
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int16_t* real_data_out) {
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int i = 0;
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int j = 0;
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int result = 0;
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int n = 1 << self->order;
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// Create the buffer specific to complex-valued FFT implementation.
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int16_t complex_buffer[2 << kMaxFFTOrder];
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// For n-point FFT, first copy the first n + 2 elements into complex
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// FFT, then construct the remaining n - 2 elements by real FFT's
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// conjugate-symmetric properties.
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memcpy(complex_buffer, complex_data_in, sizeof(int16_t) * (n + 2));
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for (i = n + 2; i < 2 * n; i += 2) {
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complex_buffer[i] = complex_data_in[2 * n - i];
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complex_buffer[i + 1] = -complex_data_in[2 * n - i + 1];
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}
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WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
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result = WebRtcSpl_ComplexIFFT(complex_buffer, self->order, 1);
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// Strip out the imaginary parts of the complex inverse FFT output.
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for (i = 0, j = 0; i < n; i += 1, j += 2) {
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real_data_out[i] = complex_buffer[j];
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}
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return result;
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}
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