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