jamulus/libs/celt/mdct.c

/* (C) 2008 Jean-Marc Valin, CSIRO
*/
/*
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   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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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. 
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "mdct.h"
#include "kfft_double.h"
#include <math.h>
#include "os_support.h"
#include "mathops.h"
#include "stack_alloc.h"

#ifndef M_PI
#define M_PI 3.141592653
#endif

void mdct_init(mdct_lookup *l,int N)
{
   int i;
   int N2;
   l->n = N;
   N2 = N>>1;
   l->kfft = cpx32_fft_alloc(N>>2);
   if (l->kfft==NULL)
     return;
   l->trig = (kiss_twiddle_scalar*)celt_alloc(N2*sizeof(kiss_twiddle_scalar));
   if (l->trig==NULL)
     return;
   /* We have enough points that sine isn't necessary */
#if defined(FIXED_POINT)
#if defined(DOUBLE_PRECISION) & !defined(MIXED_PRECISION)
   for (i=0;i<N2;i++)
      l->trig[i] = SAMP_MAX*cos(2*M_PI*(i+1./8.)/N);
#else
   for (i=0;i<N2;i++)
      l->trig[i] = TRIG_UPSCALE*celt_cos_norm(DIV32(ADD32(SHL32(EXTEND32(i),17),16386),N));
#endif
#else
   for (i=0;i<N2;i++)
      l->trig[i] = cos(2*M_PI*(i+1./8.)/N);
#endif
}

void mdct_clear(mdct_lookup *l)
{
   cpx32_fft_free(l->kfft);
   celt_free(l->trig);
}

void mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar * __restrict out, const celt_word16_t *window, int overlap)
{
   int i;
   int N, N2, N4;
   VARDECL(kiss_fft_scalar, f);
   SAVE_STACK;
   N = l->n;
   N2 = N>>1;
   N4 = N>>2;
   ALLOC(f, N2, kiss_fft_scalar);
   
   /* Consider the input to be compused of four blocks: [a, b, c, d] */
   /* Window, shuffle, fold */
   {
      /* Temp pointers to make it really clear to the compiler what we're doing */
      const kiss_fft_scalar * __restrict xp1 = in+(overlap>>1);
      const kiss_fft_scalar * __restrict xp2 = in+N2-1+(overlap>>1);
      kiss_fft_scalar * __restrict yp = out;
      const celt_word16_t * __restrict wp1 = window+(overlap>>1);
      const celt_word16_t * __restrict wp2 = window+(overlap>>1)-1;
      for(i=0;i<(overlap>>2);i++)
      {
         /* Real part arranged as -d-cR, Imag part arranged as -b+aR*/
         *yp++ = MULT16_32_Q15(*wp2, xp1[N2]) + MULT16_32_Q15(*wp1,*xp2);
         *yp++ = MULT16_32_Q15(*wp1, *xp1)    - MULT16_32_Q15(*wp2, xp2[-N2]);
         xp1+=2;
         xp2-=2;
         wp1+=2;
         wp2-=2;
      }
      wp1 = window;
      wp2 = window+overlap-1;
      for(;i<N4-(overlap>>2);i++)
      {
         /* Real part arranged as a-bR, Imag part arranged as -c-dR */
         *yp++ = *xp2;
         *yp++ = *xp1;
         xp1+=2;
         xp2-=2;
      }
      for(;i<N4;i++)
      {
         /* Real part arranged as a-bR, Imag part arranged as -c-dR */
         *yp++ =  -MULT16_32_Q15(*wp1, xp1[-N2]) + MULT16_32_Q15(*wp2, *xp2);
         *yp++ = MULT16_32_Q15(*wp2, *xp1)     + MULT16_32_Q15(*wp1, xp2[N2]);
         xp1+=2;
         xp2-=2;
         wp1+=2;
         wp2-=2;
      }
   }
   /* Pre-rotation */
   {
      kiss_fft_scalar * __restrict yp = out;
      kiss_fft_scalar *t = &l->trig[0];
      for(i=0;i<N4;i++)
      {
         kiss_fft_scalar re, im;
         re = yp[0];
         im = yp[1];
         *yp++ = -S_MUL(re,t[0])  +  S_MUL(im,t[N4]);
         *yp++ = -S_MUL(im,t[0])  -  S_MUL(re,t[N4]);
         t++;
      }
   }

   /* N/4 complex FFT, down-scales by 4/N */
   cpx32_fft(l->kfft, out, f, N4);

   /* Post-rotate */
   {
      /* Temp pointers to make it really clear to the compiler what we're doing */
      const kiss_fft_scalar * __restrict fp = f;
      kiss_fft_scalar * __restrict yp1 = out;
      kiss_fft_scalar * __restrict yp2 = out+N2-1;
      kiss_fft_scalar *t = &l->trig[0];
      /* Temp pointers to make it really clear to the compiler what we're doing */
      for(i=0;i<N4;i++)
      {
         *yp1 = -S_MUL(fp[1],t[N4]) + S_MUL(fp[0],t[0]);
         *yp2 = -S_MUL(fp[0],t[N4]) - S_MUL(fp[1],t[0]);
         fp += 2;
         yp1 += 2;
         yp2 -= 2;
         t++;
      }
   }
   RESTORE_STACK;
}


void mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar * __restrict out, const celt_word16_t * __restrict window, int overlap)
{
   int i;
   int N, N2, N4;
   VARDECL(kiss_fft_scalar, f);
   VARDECL(kiss_fft_scalar, f2);
   SAVE_STACK;
   N = l->n;
   N2 = N>>1;
   N4 = N>>2;
   ALLOC(f, N2, kiss_fft_scalar);
   ALLOC(f2, N2, kiss_fft_scalar);
   
   /* Pre-rotate */
   {
      /* Temp pointers to make it really clear to the compiler what we're doing */
      const kiss_fft_scalar * __restrict xp1 = in;
      const kiss_fft_scalar * __restrict xp2 = in+N2-1;
      kiss_fft_scalar * __restrict yp = f2;
      kiss_fft_scalar *t = &l->trig[0];
      for(i=0;i<N4;i++) 
      {
         *yp++ = -S_MUL(*xp2, t[0])  - S_MUL(*xp1,t[N4]);
         *yp++ =  S_MUL(*xp2, t[N4]) - S_MUL(*xp1,t[0]);
         xp1+=2;
         xp2-=2;
         t++;
      }
   }

   /* Inverse N/4 complex FFT. This one should *not* downscale even in fixed-point */
   cpx32_ifft(l->kfft, f2, f, N4);
   
   /* Post-rotate */
   {
      kiss_fft_scalar * __restrict fp = f;
      kiss_fft_scalar *t = &l->trig[0];

      for(i=0;i<N4;i++)
      {
         kiss_fft_scalar re, im;
         re = fp[0];
         im = fp[1];
         /* We'd scale up by 2 here, but instead it's done when mixing the windows */
         *fp++ = S_MUL(re,*t) + S_MUL(im,t[N4]);
         *fp++ = S_MUL(im,*t) - S_MUL(re,t[N4]);
         t++;
      }
   }
   /* De-shuffle the components for the middle of the window only */
   {
      const kiss_fft_scalar * __restrict fp1 = f;
      const kiss_fft_scalar * __restrict fp2 = f+N2-1;
      kiss_fft_scalar * __restrict yp = f2;
      for(i = 0; i < N4; i++)
      {
         *yp++ =-*fp1;
         *yp++ = *fp2;
         fp1 += 2;
         fp2 -= 2;
      }
   }

   /* Mirror on both sides for TDAC */
   {
      kiss_fft_scalar * __restrict fp1 = f2+N4-1;
      kiss_fft_scalar * __restrict xp1 = out+N2-1;
      kiss_fft_scalar * __restrict yp1 = out+N4-overlap/2;
      const celt_word16_t * __restrict wp1 = window;
      const celt_word16_t * __restrict wp2 = window+overlap-1;
      for(i = 0; i< N4-overlap/2; i++)
      {
         *xp1 = *fp1;
         xp1--;
         fp1--;
      }
      for(; i < N4; i++)
      {
         kiss_fft_scalar x1;
         x1 = *fp1--;
         *yp1++ +=-MULT16_32_Q15(*wp1, x1);
         *xp1-- += MULT16_32_Q15(*wp2, x1);
         wp1++;
         wp2--;
      }
   }
   {
      kiss_fft_scalar * __restrict fp2 = f2+N4;
      kiss_fft_scalar * __restrict xp2 = out+N2;
      kiss_fft_scalar * __restrict yp2 = out+N-1-(N4-overlap/2);
      const celt_word16_t * __restrict wp1 = window;
      const celt_word16_t * __restrict wp2 = window+overlap-1;
      for(i = 0; i< N4-overlap/2; i++)
      {
         *xp2 = *fp2;
         xp2++;
         fp2++;
      }
      for(; i < N4; i++)
      {
         kiss_fft_scalar x2;
         x2 = *fp2++;
         *yp2--  = MULT16_32_Q15(*wp1, x2);
         *xp2++  = MULT16_32_Q15(*wp2, x2);
         wp1++;
         wp2--;
      }
   }
   RESTORE_STACK;
}