The Tor Browser: media/libopus/celt/kiss_fft.c@b8a032363ba2 (annotated)

media/libopus/celt/kiss_fft.c@b8a032363ba2 (annotated)

media/libopus/celt/kiss_fft.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /*Copyright (c) 2003-2004, Mark Borgerding
   Lots of modifications by Jean-Marc Valin
   Copyright (c) 2005-2007, Xiph.Org Foundation
   Copyright (c) 2008,      Xiph.Org Foundation, CSIRO
   All rights reserved.
   Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
     * Redistributions of source code must retain the above copyright notice,
        this list of conditions and the following disclaimer.
     * Redistributions in binary form must reproduce the above copyright notice,
        this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.
   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   POSSIBILITY OF SUCH DAMAGE.*/
 /* This code is originally from Mark Borgerding's KISS-FFT but has been
    heavily modified to better suit Opus */
 #ifndef SKIP_CONFIG_H
 #  ifdef HAVE_CONFIG_H
 #    include "config.h"
 #  endif
 #endif
 #include "_kiss_fft_guts.h"
 #include "arch.h"
 #include "os_support.h"
 #include "mathops.h"
 #include "stack_alloc.h"
 /* The guts header contains all the multiplication and addition macros that are defined for
    complex numbers.  It also delares the kf_ internal functions.
 */
 static void kf_bfly2(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    kiss_fft_cpx * Fout2;
    const kiss_twiddle_cpx * tw1;
    int i,j;
    kiss_fft_cpx * Fout_beg = Fout;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       Fout2 = Fout + m;
       tw1 = st->twiddles;
       for(j=0;j<m;j++)
       {
          kiss_fft_cpx t;
          Fout->r = SHR32(Fout->r, 1);Fout->i = SHR32(Fout->i, 1);
          Fout2->r = SHR32(Fout2->r, 1);Fout2->i = SHR32(Fout2->i, 1);
          C_MUL (t,  *Fout2 , *tw1);
          tw1 += fstride;
          C_SUB( *Fout2 ,  *Fout , t );
          C_ADDTO( *Fout ,  t );
          ++Fout2;
          ++Fout;
       }
    }
 }
 static void ki_bfly2(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    kiss_fft_cpx * Fout2;
    const kiss_twiddle_cpx * tw1;
    kiss_fft_cpx t;
    int i,j;
    kiss_fft_cpx * Fout_beg = Fout;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       Fout2 = Fout + m;
       tw1 = st->twiddles;
       for(j=0;j<m;j++)
       {
          C_MULC (t,  *Fout2 , *tw1);
          tw1 += fstride;
          C_SUB( *Fout2 ,  *Fout , t );
          C_ADDTO( *Fout ,  t );
          ++Fout2;
          ++Fout;
       }
    }
 }
 static void kf_bfly4(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    const kiss_twiddle_cpx *tw1,*tw2,*tw3;
    kiss_fft_cpx scratch[6];
    const size_t m2=2*m;
    const size_t m3=3*m;
    int i, j;
    kiss_fft_cpx * Fout_beg = Fout;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       tw3 = tw2 = tw1 = st->twiddles;
       for (j=0;j<m;j++)
       {
          C_MUL4(scratch[0],Fout[m] , *tw1 );
          C_MUL4(scratch[1],Fout[m2] , *tw2 );
          C_MUL4(scratch[2],Fout[m3] , *tw3 );
          Fout->r = PSHR32(Fout->r, 2);
          Fout->i = PSHR32(Fout->i, 2);
          C_SUB( scratch[5] , *Fout, scratch[1] );
          C_ADDTO(*Fout, scratch[1]);
          C_ADD( scratch[3] , scratch[0] , scratch[2] );
          C_SUB( scratch[4] , scratch[0] , scratch[2] );
          C_SUB( Fout[m2], *Fout, scratch[3] );
          tw1 += fstride;
          tw2 += fstride*2;
          tw3 += fstride*3;
          C_ADDTO( *Fout , scratch[3] );
          Fout[m].r = scratch[5].r + scratch[4].i;
          Fout[m].i = scratch[5].i - scratch[4].r;
          Fout[m3].r = scratch[5].r - scratch[4].i;
          Fout[m3].i = scratch[5].i + scratch[4].r;
          ++Fout;
       }
    }
 }
 static void ki_bfly4(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    const kiss_twiddle_cpx *tw1,*tw2,*tw3;
    kiss_fft_cpx scratch[6];
    const size_t m2=2*m;
    const size_t m3=3*m;
    int i, j;
    kiss_fft_cpx * Fout_beg = Fout;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       tw3 = tw2 = tw1 = st->twiddles;
       for (j=0;j<m;j++)
       {
          C_MULC(scratch[0],Fout[m] , *tw1 );
          C_MULC(scratch[1],Fout[m2] , *tw2 );
          C_MULC(scratch[2],Fout[m3] , *tw3 );
          C_SUB( scratch[5] , *Fout, scratch[1] );
          C_ADDTO(*Fout, scratch[1]);
          C_ADD( scratch[3] , scratch[0] , scratch[2] );
          C_SUB( scratch[4] , scratch[0] , scratch[2] );
          C_SUB( Fout[m2], *Fout, scratch[3] );
          tw1 += fstride;
          tw2 += fstride*2;
          tw3 += fstride*3;
          C_ADDTO( *Fout , scratch[3] );
          Fout[m].r = scratch[5].r - scratch[4].i;
          Fout[m].i = scratch[5].i + scratch[4].r;
          Fout[m3].r = scratch[5].r + scratch[4].i;
          Fout[m3].i = scratch[5].i - scratch[4].r;
          ++Fout;
       }
    }
 }
 #ifndef RADIX_TWO_ONLY
 static void kf_bfly3(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    int i;
    size_t k;
    const size_t m2 = 2*m;
    const kiss_twiddle_cpx *tw1,*tw2;
    kiss_fft_cpx scratch[5];
    kiss_twiddle_cpx epi3;
    kiss_fft_cpx * Fout_beg = Fout;
    epi3 = st->twiddles[fstride*m];
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       tw1=tw2=st->twiddles;
       k=m;
       do {
          C_FIXDIV(*Fout,3); C_FIXDIV(Fout[m],3); C_FIXDIV(Fout[m2],3);
          C_MUL(scratch[1],Fout[m] , *tw1);
          C_MUL(scratch[2],Fout[m2] , *tw2);
          C_ADD(scratch[3],scratch[1],scratch[2]);
          C_SUB(scratch[0],scratch[1],scratch[2]);
          tw1 += fstride;
          tw2 += fstride*2;
          Fout[m].r = Fout->r - HALF_OF(scratch[3].r);
          Fout[m].i = Fout->i - HALF_OF(scratch[3].i);
          C_MULBYSCALAR( scratch[0] , epi3.i );
          C_ADDTO(*Fout,scratch[3]);
          Fout[m2].r = Fout[m].r + scratch[0].i;
          Fout[m2].i = Fout[m].i - scratch[0].r;
          Fout[m].r -= scratch[0].i;
          Fout[m].i += scratch[0].r;
          ++Fout;
       } while(--k);
    }
 }
 static void ki_bfly3(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    int i, k;
    const size_t m2 = 2*m;
    const kiss_twiddle_cpx *tw1,*tw2;
    kiss_fft_cpx scratch[5];
    kiss_twiddle_cpx epi3;
    kiss_fft_cpx * Fout_beg = Fout;
    epi3 = st->twiddles[fstride*m];
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       tw1=tw2=st->twiddles;
       k=m;
       do{
          C_MULC(scratch[1],Fout[m] , *tw1);
          C_MULC(scratch[2],Fout[m2] , *tw2);
          C_ADD(scratch[3],scratch[1],scratch[2]);
          C_SUB(scratch[0],scratch[1],scratch[2]);
          tw1 += fstride;
          tw2 += fstride*2;
          Fout[m].r = Fout->r - HALF_OF(scratch[3].r);
          Fout[m].i = Fout->i - HALF_OF(scratch[3].i);
          C_MULBYSCALAR( scratch[0] , -epi3.i );
          C_ADDTO(*Fout,scratch[3]);
          Fout[m2].r = Fout[m].r + scratch[0].i;
          Fout[m2].i = Fout[m].i - scratch[0].r;
          Fout[m].r -= scratch[0].i;
          Fout[m].i += scratch[0].r;
          ++Fout;
       }while(--k);
    }
 }
 static void kf_bfly5(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    kiss_fft_cpx *Fout0,*Fout1,*Fout2,*Fout3,*Fout4;
    int i, u;
    kiss_fft_cpx scratch[13];
    const kiss_twiddle_cpx * twiddles = st->twiddles;
    const kiss_twiddle_cpx *tw;
    kiss_twiddle_cpx ya,yb;
    kiss_fft_cpx * Fout_beg = Fout;
    ya = twiddles[fstride*m];
    yb = twiddles[fstride*2*m];
    tw=st->twiddles;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       Fout0=Fout;
       Fout1=Fout0+m;
       Fout2=Fout0+2*m;
       Fout3=Fout0+3*m;
       Fout4=Fout0+4*m;
       for ( u=0; u<m; ++u ) {
          C_FIXDIV( *Fout0,5); C_FIXDIV( *Fout1,5); C_FIXDIV( *Fout2,5); C_FIXDIV( *Fout3,5); C_FIXDIV( *Fout4,5);
          scratch[0] = *Fout0;
          C_MUL(scratch[1] ,*Fout1, tw[u*fstride]);
          C_MUL(scratch[2] ,*Fout2, tw[2*u*fstride]);
          C_MUL(scratch[3] ,*Fout3, tw[3*u*fstride]);
          C_MUL(scratch[4] ,*Fout4, tw[4*u*fstride]);
          C_ADD( scratch[7],scratch[1],scratch[4]);
          C_SUB( scratch[10],scratch[1],scratch[4]);
          C_ADD( scratch[8],scratch[2],scratch[3]);
          C_SUB( scratch[9],scratch[2],scratch[3]);
          Fout0->r += scratch[7].r + scratch[8].r;
          Fout0->i += scratch[7].i + scratch[8].i;
          scratch[5].r = scratch[0].r + S_MUL(scratch[7].r,ya.r) + S_MUL(scratch[8].r,yb.r);
          scratch[5].i = scratch[0].i + S_MUL(scratch[7].i,ya.r) + S_MUL(scratch[8].i,yb.r);
          scratch[6].r =  S_MUL(scratch[10].i,ya.i) + S_MUL(scratch[9].i,yb.i);
          scratch[6].i = -S_MUL(scratch[10].r,ya.i) - S_MUL(scratch[9].r,yb.i);
          C_SUB(*Fout1,scratch[5],scratch[6]);
          C_ADD(*Fout4,scratch[5],scratch[6]);
          scratch[11].r = scratch[0].r + S_MUL(scratch[7].r,yb.r) + S_MUL(scratch[8].r,ya.r);
          scratch[11].i = scratch[0].i + S_MUL(scratch[7].i,yb.r) + S_MUL(scratch[8].i,ya.r);
          scratch[12].r = - S_MUL(scratch[10].i,yb.i) + S_MUL(scratch[9].i,ya.i);
          scratch[12].i = S_MUL(scratch[10].r,yb.i) - S_MUL(scratch[9].r,ya.i);
          C_ADD(*Fout2,scratch[11],scratch[12]);
          C_SUB(*Fout3,scratch[11],scratch[12]);
          ++Fout0;++Fout1;++Fout2;++Fout3;++Fout4;
       }
    }
 }
 static void ki_bfly5(
                      kiss_fft_cpx * Fout,
                      const size_t fstride,
                      const kiss_fft_state *st,
                      int m,
                      int N,
                      int mm
                     )
 {
    kiss_fft_cpx *Fout0,*Fout1,*Fout2,*Fout3,*Fout4;
    int i, u;
    kiss_fft_cpx scratch[13];
    const kiss_twiddle_cpx * twiddles = st->twiddles;
    const kiss_twiddle_cpx *tw;
    kiss_twiddle_cpx ya,yb;
    kiss_fft_cpx * Fout_beg = Fout;
    ya = twiddles[fstride*m];
    yb = twiddles[fstride*2*m];
    tw=st->twiddles;
    for (i=0;i<N;i++)
    {
       Fout = Fout_beg + i*mm;
       Fout0=Fout;
       Fout1=Fout0+m;
       Fout2=Fout0+2*m;
       Fout3=Fout0+3*m;
       Fout4=Fout0+4*m;
       for ( u=0; u<m; ++u ) {
          scratch[0] = *Fout0;
          C_MULC(scratch[1] ,*Fout1, tw[u*fstride]);
          C_MULC(scratch[2] ,*Fout2, tw[2*u*fstride]);
          C_MULC(scratch[3] ,*Fout3, tw[3*u*fstride]);
          C_MULC(scratch[4] ,*Fout4, tw[4*u*fstride]);
          C_ADD( scratch[7],scratch[1],scratch[4]);
          C_SUB( scratch[10],scratch[1],scratch[4]);
          C_ADD( scratch[8],scratch[2],scratch[3]);
          C_SUB( scratch[9],scratch[2],scratch[3]);
          Fout0->r += scratch[7].r + scratch[8].r;
          Fout0->i += scratch[7].i + scratch[8].i;
          scratch[5].r = scratch[0].r + S_MUL(scratch[7].r,ya.r) + S_MUL(scratch[8].r,yb.r);
          scratch[5].i = scratch[0].i + S_MUL(scratch[7].i,ya.r) + S_MUL(scratch[8].i,yb.r);
          scratch[6].r = -S_MUL(scratch[10].i,ya.i) - S_MUL(scratch[9].i,yb.i);
          scratch[6].i =  S_MUL(scratch[10].r,ya.i) + S_MUL(scratch[9].r,yb.i);
          C_SUB(*Fout1,scratch[5],scratch[6]);
          C_ADD(*Fout4,scratch[5],scratch[6]);
          scratch[11].r = scratch[0].r + S_MUL(scratch[7].r,yb.r) + S_MUL(scratch[8].r,ya.r);
          scratch[11].i = scratch[0].i + S_MUL(scratch[7].i,yb.r) + S_MUL(scratch[8].i,ya.r);
          scratch[12].r =  S_MUL(scratch[10].i,yb.i) - S_MUL(scratch[9].i,ya.i);
          scratch[12].i = -S_MUL(scratch[10].r,yb.i) + S_MUL(scratch[9].r,ya.i);
          C_ADD(*Fout2,scratch[11],scratch[12]);
          C_SUB(*Fout3,scratch[11],scratch[12]);
          ++Fout0;++Fout1;++Fout2;++Fout3;++Fout4;
       }
    }
 }
 #endif
 #ifdef CUSTOM_MODES
 static
 void compute_bitrev_table(
          int Fout,
          opus_int16 *f,
          const size_t fstride,
          int in_stride,
          opus_int16 * factors,
          const kiss_fft_state *st
             )
 {
    const int p=*factors++; /* the radix  */
    const int m=*factors++; /* stage's fft length/p */
     /*printf ("fft %d %d %d %d %d %d\n", p*m, m, p, s2, fstride*in_stride, N);*/
    if (m==1)
    {
       int j;
       for (j=0;j<p;j++)
       {
          *f = Fout+j;
          f += fstride*in_stride;
       }
    } else {
       int j;
       for (j=0;j<p;j++)
       {
          compute_bitrev_table( Fout , f, fstride*p, in_stride, factors,st);
          f += fstride*in_stride;
          Fout += m;
       }
    }
 }
 /*  facbuf is populated by p1,m1,p2,m2, ...
     where
     p[i] * m[i] = m[i-1]
     m0 = n                  */
 static
 int kf_factor(int n,opus_int16 * facbuf)
 {
     int p=4;
     /*factor out powers of 4, powers of 2, then any remaining primes */
     do {
         while (n % p) {
             switch (p) {
                 case 4: p = 2; break;
                 case 2: p = 3; break;
                 default: p += 2; break;
             }
             if (p>32000 || (opus_int32)p*(opus_int32)p > n)
                 p = n;          /* no more factors, skip to end */
         }
         n /= p;
 #ifdef RADIX_TWO_ONLY
         if (p!=2 && p != 4)
 #else
         if (p>5)
 #endif
         {
            return 0;
         }
         *facbuf++ = p;
         *facbuf++ = n;
     } while (n > 1);
     return 1;
 }
 static void compute_twiddles(kiss_twiddle_cpx *twiddles, int nfft)
 {
    int i;
 #ifdef FIXED_POINT
    for (i=0;i<nfft;++i) {
       opus_val32 phase = -i;
       kf_cexp2(twiddles+i, DIV32(SHL32(phase,17),nfft));
    }
 #else
    for (i=0;i<nfft;++i) {
       const double pi=3.14159265358979323846264338327;
       double phase = ( -2*pi /nfft ) * i;
       kf_cexp(twiddles+i, phase );
    }
 #endif
 }
 /*
  *
  * Allocates all necessary storage space for the fft and ifft.
  * The return value is a contiguous block of memory.  As such,
  * It can be freed with free().
  * */
 kiss_fft_state *opus_fft_alloc_twiddles(int nfft,void * mem,size_t * lenmem,  const kiss_fft_state *base)
 {
     kiss_fft_state *st=NULL;
     size_t memneeded = sizeof(struct kiss_fft_state); /* twiddle factors*/
     if ( lenmem==NULL ) {
         st = ( kiss_fft_state*)KISS_FFT_MALLOC( memneeded );
     }else{
         if (mem != NULL && *lenmem >= memneeded)
             st = (kiss_fft_state*)mem;
         *lenmem = memneeded;
     }
     if (st) {
         opus_int16 *bitrev;
         kiss_twiddle_cpx *twiddles;
         st->nfft=nfft;
 #ifndef FIXED_POINT
         st->scale = 1.f/nfft;
 #endif
         if (base != NULL)
         {
            st->twiddles = base->twiddles;
            st->shift = 0;
            while (nfft<<st->shift != base->nfft && st->shift < 32)
               st->shift++;
            if (st->shift>=32)
               goto fail;
         } else {
            st->twiddles = twiddles = (kiss_twiddle_cpx*)KISS_FFT_MALLOC(sizeof(kiss_twiddle_cpx)*nfft);
            compute_twiddles(twiddles, nfft);
            st->shift = -1;
         }
         if (!kf_factor(nfft,st->factors))
         {
            goto fail;
         }
         /* bitrev */
         st->bitrev = bitrev = (opus_int16*)KISS_FFT_MALLOC(sizeof(opus_int16)*nfft);
         if (st->bitrev==NULL)
             goto fail;
         compute_bitrev_table(0, bitrev, 1,1, st->factors,st);
     }
     return st;
 fail:
     opus_fft_free(st);
     return NULL;
 }
 kiss_fft_state *opus_fft_alloc(int nfft,void * mem,size_t * lenmem )
 {
    return opus_fft_alloc_twiddles(nfft, mem, lenmem, NULL);
 }
 void opus_fft_free(const kiss_fft_state *cfg)
 {
    if (cfg)
    {
       opus_free((opus_int16*)cfg->bitrev);
       if (cfg->shift < 0)
          opus_free((kiss_twiddle_cpx*)cfg->twiddles);
       opus_free((kiss_fft_state*)cfg);
    }
 }
 #endif /* CUSTOM_MODES */
 void opus_fft(const kiss_fft_state *st,const kiss_fft_cpx *fin,kiss_fft_cpx *fout)
 {
     int m2, m;
     int p;
     int L;
     int fstride[MAXFACTORS];
     int i;
     int shift;
     /* st->shift can be -1 */
     shift = st->shift>0 ? st->shift : 0;
     celt_assert2 (fin != fout, "In-place FFT not supported");
     /* Bit-reverse the input */
     for (i=0;i<st->nfft;i++)
     {
        fout[st->bitrev[i]] = fin[i];
 #ifndef FIXED_POINT
        fout[st->bitrev[i]].r *= st->scale;
        fout[st->bitrev[i]].i *= st->scale;
 #endif
     }
     fstride[0] = 1;
     L=0;
     do {
        p = st->factors[2*L];
        m = st->factors[2*L+1];
        fstride[L+1] = fstride[L]*p;
        L++;
     } while(m!=1);
     m = st->factors[2*L-1];
     for (i=L-1;i>=0;i--)
     {
        if (i!=0)
           m2 = st->factors[2*i-1];
        else
           m2 = 1;
        switch (st->factors[2*i])
        {
        case 2:
           kf_bfly2(fout,fstride[i]<<shift,st,m, fstride[i], m2);
           break;
        case 4:
           kf_bfly4(fout,fstride[i]<<shift,st,m, fstride[i], m2);
           break;
  #ifndef RADIX_TWO_ONLY
        case 3:
           kf_bfly3(fout,fstride[i]<<shift,st,m, fstride[i], m2);
           break;
        case 5:
           kf_bfly5(fout,fstride[i]<<shift,st,m, fstride[i], m2);
           break;
  #endif
        }
        m = m2;
     }
 }
 void opus_ifft(const kiss_fft_state *st,const kiss_fft_cpx *fin,kiss_fft_cpx *fout)
 {
    int m2, m;
    int p;
    int L;
    int fstride[MAXFACTORS];
    int i;
    int shift;
    /* st->shift can be -1 */
    shift = st->shift>0 ? st->shift : 0;
    celt_assert2 (fin != fout, "In-place FFT not supported");
    /* Bit-reverse the input */
    for (i=0;i<st->nfft;i++)
       fout[st->bitrev[i]] = fin[i];
    fstride[0] = 1;
    L=0;
    do {
       p = st->factors[2*L];
       m = st->factors[2*L+1];
       fstride[L+1] = fstride[L]*p;
       L++;
    } while(m!=1);
    m = st->factors[2*L-1];
    for (i=L-1;i>=0;i--)
    {
       if (i!=0)
          m2 = st->factors[2*i-1];
       else
          m2 = 1;
       switch (st->factors[2*i])
       {
       case 2:
          ki_bfly2(fout,fstride[i]<<shift,st,m, fstride[i], m2);
          break;
       case 4:
          ki_bfly4(fout,fstride[i]<<shift,st,m, fstride[i], m2);
          break;
 #ifndef RADIX_TWO_ONLY
       case 3:
          ki_bfly3(fout,fstride[i]<<shift,st,m, fstride[i], m2);
          break;
       case 5:
          ki_bfly5(fout,fstride[i]<<shift,st,m, fstride[i], m2);
          break;
 #endif
       }
       m = m2;
    }
 }

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media/libopus/celt/kiss_fft.c@b8a032363ba2 (annotated)

media/libopus/celt/kiss_fft.c