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 #ifndef WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_ 12 #define WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_ 13 14 #include "webrtc/typedefs.h" 15 16 // For ComplexFFT(), the maximum fft order is 10; 17 // for OpenMax FFT in ARM, it is 12; 18 // WebRTC APM uses orders of only 7 and 8. 19 enum {kMaxFFTOrder = 10}; 20 21 struct RealFFT; 22 23 #ifdef __cplusplus 24 extern "C" { 25 #endif 26 27 struct RealFFT* WebRtcSpl_CreateRealFFT(int order); 28 void WebRtcSpl_FreeRealFFT(struct RealFFT* self); 29 30 // Compute an FFT for a real-valued signal of length of 2^order, 31 // where 1 < order <= MAX_FFT_ORDER. Transform length is determined by the 32 // specification structure, which must be initialized prior to calling the FFT 33 // function with WebRtcSpl_CreateRealFFT(). 34 // The relationship between the input and output sequences can 35 // be expressed in terms of the DFT, i.e.: 36 // x[n] = (2^(-scalefactor)/N) . SUM[k=0,...,N-1] X[k].e^(jnk.2.pi/N) 37 // n=0,1,2,...N-1 38 // N=2^order. 39 // The conjugate-symmetric output sequence is represented using a CCS vector, 40 // which is of length N+2, and is organized as follows: 41 // Index: 0 1 2 3 4 5 . . . N-2 N-1 N N+1 42 // Component: R0 0 R1 I1 R2 I2 . . . R[N/2-1] I[N/2-1] R[N/2] 0 43 // where R[n] and I[n], respectively, denote the real and imaginary components 44 // for FFT bin 'n'. Bins are numbered from 0 to N/2, where N is the FFT length. 45 // Bin index 0 corresponds to the DC component, and bin index N/2 corresponds to 46 // the foldover frequency. 47 // 48 // Input Arguments: 49 // self - pointer to preallocated and initialized FFT specification structure. 50 // real_data_in - the input signal. For an ARM Neon platform, it must be 51 // aligned on a 32-byte boundary. 52 // 53 // Output Arguments: 54 // complex_data_out - the output complex signal with (2^order + 2) 16-bit 55 // elements. For an ARM Neon platform, it must be different 56 // from real_data_in, and aligned on a 32-byte boundary. 57 // 58 // Return Value: 59 // 0 - FFT calculation is successful. 60 // -1 - Error with bad arguments (NULL pointers). 61 int WebRtcSpl_RealForwardFFT(struct RealFFT* self, 62 const int16_t* real_data_in, 63 int16_t* complex_data_out); 64 65 // Compute the inverse FFT for a conjugate-symmetric input sequence of length of 66 // 2^order, where 1 < order <= MAX_FFT_ORDER. Transform length is determined by 67 // the specification structure, which must be initialized prior to calling the 68 // FFT function with WebRtcSpl_CreateRealFFT(). 69 // For a transform of length M, the input sequence is represented using a packed 70 // CCS vector of length M+2, which is explained in the comments for 71 // WebRtcSpl_RealForwardFFTC above. 72 // 73 // Input Arguments: 74 // self - pointer to preallocated and initialized FFT specification structure. 75 // complex_data_in - the input complex signal with (2^order + 2) 16-bit 76 // elements. For an ARM Neon platform, it must be aligned on 77 // a 32-byte boundary. 78 // 79 // Output Arguments: 80 // real_data_out - the output real signal. For an ARM Neon platform, it must 81 // be different to complex_data_in, and aligned on a 32-byte 82 // boundary. 83 // 84 // Return Value: 85 // 0 or a positive number - a value that the elements in the |real_data_out| 86 // should be shifted left with in order to get 87 // correct physical values. 88 // -1 - Error with bad arguments (NULL pointers). 89 int WebRtcSpl_RealInverseFFT(struct RealFFT* self, 90 const int16_t* complex_data_in, 91 int16_t* real_data_out); 92 93 #ifdef __cplusplus 94 } 95 #endif 96 97 #endif // WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_ 98