libcelt/mdct.h

/* Copyright (c) 2007-2008 CSIRO
   Copyright (c) 2007-2008 Xiph.Org Foundation
   Written by Jean-Marc Valin */
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/* This is a simple MDCT implementation that uses a N/4 complex FFT
   to do most of the work. It should be relatively straightforward to
   plug in pretty much and FFT here.
   
   This replaces the Vorbis FFT (and uses the exact same API), which 
   was a bit too messy and that was ending up duplicating code 
   (might as well use the same FFT everywhere).
   
   The algorithm is similar to (and inspired from) Fabrice Bellard's
   MDCT implementation in FFMPEG, but has differences in signs, ordering
   and scaling in many places. 
*/

#ifndef MDCT_H
#define MDCT_H

#include "kiss_fft.h"
#include "arch.h"

typedef struct {
   int n;
   int maxshift;
   const kiss_fft_state *kfft[4];
   const kiss_twiddle_scalar * restrict trig;
} mdct_lookup;

void clt_mdct_init(mdct_lookup *l,int N, int maxshift);
void clt_mdct_clear(mdct_lookup *l);

/** Compute a forward MDCT and scale by 4/N */
void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar *out, const celt_word16 *window, int overlap, int shift);

/** Compute a backward MDCT (no scaling) and performs weighted overlap-add 
    (scales implicitly by 1/2) */
void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar *out, const celt_word16 * restrict window, int overlap, int shift);

#endif