Line data    Source code

       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           0 : struct RealFFT* WebRtcSpl_CreateRealFFT(int order) {
      22           0 :   struct RealFFT* self = NULL;
      23             : 
      24           0 :   if (order > kMaxFFTOrder || order < 0) {
      25           0 :     return NULL;
      26             :   }
      27             : 
      28           0 :   self = malloc(sizeof(struct RealFFT));
      29           0 :   if (self == NULL) {
      30           0 :     return NULL;
      31             :   }
      32           0 :   self->order = order;
      33             : 
      34           0 :   return self;
      35             : }
      36             : 
      37           0 : void WebRtcSpl_FreeRealFFT(struct RealFFT* self) {
      38           0 :   if (self != NULL) {
      39           0 :     free(self);
      40             :   }
      41           0 : }
      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           0 : int WebRtcSpl_RealForwardFFT(struct RealFFT* self,
      48             :                              const int16_t* real_data_in,
      49             :                              int16_t* complex_data_out) {
      50           0 :   int i = 0;
      51           0 :   int j = 0;
      52           0 :   int result = 0;
      53           0 :   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           0 :   for (i = 0, j = 0; i < n; i += 1, j += 2) {
      60           0 :     complex_buffer[j] = real_data_in[i];
      61           0 :     complex_buffer[j + 1] = 0;
      62             :   };
      63             : 
      64           0 :   WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
      65           0 :   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           0 :   memcpy(complex_data_out, complex_buffer, sizeof(int16_t) * (n + 2));
      70             : 
      71           0 :   return result;
      72             : }
      73             : 
      74           0 : int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
      75             :                              const int16_t* complex_data_in,
      76             :                              int16_t* real_data_out) {
      77           0 :   int i = 0;
      78           0 :   int j = 0;
      79           0 :   int result = 0;
      80           0 :   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           0 :   memcpy(complex_buffer, complex_data_in, sizeof(int16_t) * (n + 2));
      88           0 :   for (i = n + 2; i < 2 * n; i += 2) {
      89           0 :     complex_buffer[i] = complex_data_in[2 * n - i];
      90           0 :     complex_buffer[i + 1] = -complex_data_in[2 * n - i + 1];
      91             :   }
      92             : 
      93           0 :   WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
      94           0 :   result = WebRtcSpl_ComplexIFFT(complex_buffer, self->order, 1);
      95             : 
      96             :   // Strip out the imaginary parts of the complex inverse FFT output.
      97           0 :   for (i = 0, j = 0; i < n; i += 1, j += 2) {
      98           0 :     real_data_out[i] = complex_buffer[j];
      99             :   }
     100             : 
     101           0 :   return result;
     102             : }