Add copy of opus library in deps/third_party.

opus/celt/kiss_fft.c

+/*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"
+#include "os_support.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] );
+         Fout[m2].r = PSHR32(Fout[m2].r, 2);
+         Fout[m2].i = PSHR32(Fout[m2].i, 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;
+   }
+}
+