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 /* * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. * * Use of this source code is governed by a BSD-style license * that can be found in the LICENSE file in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. */ #ifndef COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_ #define COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_ #include // For ComplexFFT(), the maximum fft order is 10; // WebRTC APM uses orders of only 7 and 8. enum { kMaxFFTOrder = 10 }; struct RealFFT; #ifdef __cplusplus extern "C" { #endif struct RealFFT* WebRtcSpl_CreateRealFFT(int order); void WebRtcSpl_FreeRealFFT(struct RealFFT* self); // Compute an FFT for a real-valued signal of length of 2^order, // where 1 < order <= MAX_FFT_ORDER. Transform length is determined by the // specification structure, which must be initialized prior to calling the FFT // function with WebRtcSpl_CreateRealFFT(). // The relationship between the input and output sequences can // be expressed in terms of the DFT, i.e.: // x[n] = (2^(-scalefactor)/N) . SUM[k=0,...,N-1] X[k].e^(jnk.2.pi/N) // n=0,1,2,...N-1 // N=2^order. // The conjugate-symmetric output sequence is represented using a CCS vector, // which is of length N+2, and is organized as follows: // Index: 0 1 2 3 4 5 . . . N-2 N-1 N N+1 // Component: R0 0 R1 I1 R2 I2 . . . R[N/2-1] I[N/2-1] R[N/2] 0 // where R[n] and I[n], respectively, denote the real and imaginary components // for FFT bin 'n'. Bins are numbered from 0 to N/2, where N is the FFT length. // Bin index 0 corresponds to the DC component, and bin index N/2 corresponds to // the foldover frequency. // // Input Arguments: // self - pointer to preallocated and initialized FFT specification structure. // real_data_in - the input signal. For an ARM Neon platform, it must be // aligned on a 32-byte boundary. // // Output Arguments: // complex_data_out - the output complex signal with (2^order + 2) 16-bit // elements. For an ARM Neon platform, it must be different // from real_data_in, and aligned on a 32-byte boundary. // // Return Value: // 0 - FFT calculation is successful. // -1 - Error with bad arguments (null pointers). int WebRtcSpl_RealForwardFFT(struct RealFFT* self, const int16_t* real_data_in, int16_t* complex_data_out); // Compute the inverse FFT for a conjugate-symmetric input sequence of length of // 2^order, where 1 < order <= MAX_FFT_ORDER. Transform length is determined by // the specification structure, which must be initialized prior to calling the // FFT function with WebRtcSpl_CreateRealFFT(). // For a transform of length M, the input sequence is represented using a packed // CCS vector of length M+2, which is explained in the comments for // WebRtcSpl_RealForwardFFTC above. // // Input Arguments: // self - pointer to preallocated and initialized FFT specification structure. // complex_data_in - the input complex signal with (2^order + 2) 16-bit // elements. For an ARM Neon platform, it must be aligned on // a 32-byte boundary. // // Output Arguments: // real_data_out - the output real signal. For an ARM Neon platform, it must // be different to complex_data_in, and aligned on a 32-byte // boundary. // // Return Value: // 0 or a positive number - a value that the elements in the `real_data_out` // should be shifted left with in order to get // correct physical values. // -1 - Error with bad arguments (null pointers). int WebRtcSpl_RealInverseFFT(struct RealFFT* self, const int16_t* complex_data_in, int16_t* real_data_out); #ifdef __cplusplus } #endif #endif // COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_