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Making the MDCT produce interleaved data

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -401,32 +401,24 @@

    if (C==1 && !shortBlocks)

    {

       const int overlap = OVERLAP(mode);

-      clt_mdct_forward(&mode->mdct, in, out, mode->window, overlap, mode->maxLM-LM);

+      clt_mdct_forward(&mode->mdct, in, out, mode->window, overlap, mode->maxLM-LM, 1);

    } else {

       const int overlap = OVERLAP(mode);

       int N = mode->shortMdctSize<<LM;

       int B = 1;

       int b, c;

-      VARDECL(opus_val32, tmp);

-      SAVE_STACK;

       if (shortBlocks)

       {

-         /*lookup = &mode->mdct[0];*/

          N = mode->shortMdctSize;

          B = shortBlocks;

       }

-      ALLOC(tmp, N, opus_val32);

       c=0; do {

          for (b=0;b<B;b++)

          {

-            int j;

-            clt_mdct_forward(&mode->mdct, in+c*(B*N+overlap)+b*N, tmp, mode->window, overlap, shortBlocks ? mode->maxLM : mode->maxLM-LM);

-            /* Interleaving the sub-frames */

-            for (j=0;j<N;j++)

-               out[(j*B+b)+c*N*B] = tmp[j];

+            /* Interleaving the sub-frames while doing the MDCTs */

+            clt_mdct_forward(&mode->mdct, in+c*(B*N+overlap)+b*N, &out[b+c*N*B], mode->window, overlap, shortBlocks ? mode->maxLM : mode->maxLM-LM, B);

          }

       } while (++c<C);

-      RESTORE_STACK;

    }

 }

--- a/libcelt/mdct.c

+++ b/libcelt/mdct.c

@@ -99,7 +99,8 @@

 #endif /* CUSTOM_MODES */

-void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar * restrict out, const opus_val16 *window, int overlap, int shift)

+void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar * restrict out,

+      const opus_val16 *window, int overlap, int shift, int stride)

 {

    int i;

    int N, N2, N4;

@@ -124,7 +125,7 @@

       /* 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;

+      kiss_fft_scalar * restrict yp = f;

       const opus_val16 * restrict wp1 = window+(overlap>>1);

       const opus_val16 * restrict wp2 = window+(overlap>>1)-1;

       for(i=0;i<(overlap>>2);i++)

@@ -160,7 +161,7 @@

    }

    /* Pre-rotation */

    {

-      kiss_fft_scalar * restrict yp = out;

+      kiss_fft_scalar * restrict yp = f;

       const kiss_twiddle_scalar *t = &l->trig[0];

       for(i=0;i<N4;i++)

       {

@@ -176,14 +177,14 @@

    }

    /* N/4 complex FFT, down-scales by 4/N */

-   opus_fft(l->kfft[shift], (kiss_fft_cpx *)out, (kiss_fft_cpx *)f);

+   opus_fft(l->kfft[shift], (kiss_fft_cpx *)f, (kiss_fft_cpx *)in);

    /* Post-rotate */

    {

       /* Temp pointers to make it really clear to the compiler what we're doing */

-      const kiss_fft_scalar * restrict fp = f;

+      const kiss_fft_scalar * restrict fp = in;

       kiss_fft_scalar * restrict yp1 = out;

-      kiss_fft_scalar * restrict yp2 = out+N2-1;

+      kiss_fft_scalar * restrict yp2 = out+stride*(N2-1);

       const kiss_twiddle_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++)

@@ -195,8 +196,8 @@

          *yp1 = yr - S_MUL(yi,sine);

          *yp2 = yi + S_MUL(yr,sine);;

          fp += 2;

-         yp1 += 2;

-         yp2 -= 2;

+         yp1 += 2*stride;

+         yp2 -= 2*stride;

       }

    }

    RESTORE_STACK;

--- a/libcelt/mdct.h

+++ b/libcelt/mdct.h

@@ -56,7 +56,8 @@

 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 opus_val16 *window, int overlap, int shift);

+void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar *out,

+      const opus_val16 *window, int overlap, int shift, int stride);

 /** Compute a backward MDCT (no scaling) and performs weighted overlap-add

     (scales implicitly by 1/2) */

--- a/libcelt/tests/mdct-test.c

+++ b/libcelt/tests/mdct-test.c

@@ -93,6 +93,7 @@

     size_t buflen = sizeof(kiss_fft_scalar)*nfft;

     kiss_fft_scalar  * in = (kiss_fft_scalar*)malloc(buflen);

+    kiss_fft_scalar  * in_copy = (kiss_fft_scalar*)malloc(buflen);

     kiss_fft_scalar  * out= (kiss_fft_scalar*)malloc(buflen);

     opus_val16  * window= (opus_val16*)malloc(sizeof(opus_val16)*nfft/2);

     int k;

@@ -116,6 +117,8 @@

        }

     }

+    for (k=0;k<nfft;++k)

+       in_copy[k] = in[k];

     /*for (k=0;k<nfft;++k) printf("%d %d ", in[k].r, in[k].i);printf("\n");*/

     if (isinverse)

@@ -125,8 +128,8 @@

        clt_mdct_backward(&cfg,in,out, window, nfft/2, 0, 1);

        check_inv(in,out,nfft,isinverse);

     } else {

-       clt_mdct_forward(&cfg,in,out,window, nfft/2, 0);

-       check(in,out,nfft,isinverse);

+       clt_mdct_forward(&cfg,in,out,window, nfft/2, 0, 1);

+       check(in_copy,out,nfft,isinverse);

     }

     /*for (k=0;k<nfft;++k) printf("%d %d ", out[k].r, out[k].i);printf("\n");*/