libavcodec/fft.c - vendor/opensource/ffmpeg - Git at Google

 /*
  * FFT/IFFT transforms
  * Copyright (c) 2008 Loren Merritt
  * Copyright (c) 2002 Fabrice Bellard
  * Partly based on libdjbfft by D. J. Bernstein
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */

 /**
  * @file libavcodec/fft.c
  * FFT/IFFT transforms.
  */

 #include "dsputil.h"

 /* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
 DECLARE_ALIGNED_16(FFTSample, ff_cos_16[8]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_32[16]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_64[32]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_128[64]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_256[128]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_512[256]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_1024[512]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_2048[1024]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_4096[2048]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_8192[4096]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_16384[8192]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_32768[16384]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_65536[32768]);
 FFTSample *ff_cos_tabs[] = {
     ff_cos_16, ff_cos_32, ff_cos_64, ff_cos_128, ff_cos_256, ff_cos_512, ff_cos_1024,
     ff_cos_2048, ff_cos_4096, ff_cos_8192, ff_cos_16384, ff_cos_32768, ff_cos_65536,
 };

 static int split_radix_permutation(int i, int n, int inverse)
 {
     int m;
     if(n <= 2) return i&1;
     m = n >> 1;
     if(!(i&m))            return split_radix_permutation(i, m, inverse)*2;
     m >>= 1;
     if(inverse == !(i&m)) return split_radix_permutation(i, m, inverse)*4 + 1;
     else                  return split_radix_permutation(i, m, inverse)*4 - 1;
 }

 av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
 {
     int i, j, m, n;
     float alpha, c1, s1, s2;
     int split_radix = 1;
     int av_unused has_vectors;

     if (nbits < 2 || nbits > 16)
         goto fail;
     s->nbits = nbits;
     n = 1 << nbits;

     s->tmp_buf = NULL;
     s->exptab  = av_malloc((n / 2) * sizeof(FFTComplex));
     if (!s->exptab)
         goto fail;
     s->revtab = av_malloc(n * sizeof(uint16_t));
     if (!s->revtab)
         goto fail;
     s->inverse = inverse;

     s2 = inverse ? 1.0 : -1.0;

     s->fft_permute = ff_fft_permute_c;
     s->fft_calc    = ff_fft_calc_c;
     s->imdct_calc  = ff_imdct_calc_c;
     s->imdct_half  = ff_imdct_half_c;
     s->exptab1     = NULL;

 #if HAVE_MMX && HAVE_YASM
     has_vectors = mm_support();
     if (has_vectors & FF_MM_SSE && HAVE_SSE) {
         /* SSE for P3/P4/K8 */
         s->imdct_calc  = ff_imdct_calc_sse;
         s->imdct_half  = ff_imdct_half_sse;
         s->fft_permute = ff_fft_permute_sse;
         s->fft_calc    = ff_fft_calc_sse;
     } else if (has_vectors & FF_MM_3DNOWEXT && HAVE_AMD3DNOWEXT) {
         /* 3DNowEx for K7 */
         s->imdct_calc = ff_imdct_calc_3dn2;
         s->imdct_half = ff_imdct_half_3dn2;
         s->fft_calc   = ff_fft_calc_3dn2;
     } else if (has_vectors & FF_MM_3DNOW && HAVE_AMD3DNOW) {
         /* 3DNow! for K6-2/3 */
         s->imdct_calc = ff_imdct_calc_3dn;
         s->imdct_half = ff_imdct_half_3dn;
         s->fft_calc   = ff_fft_calc_3dn;
     }
 #elif HAVE_ALTIVEC
     has_vectors = mm_support();
     if (has_vectors & FF_MM_ALTIVEC) {
         s->fft_calc = ff_fft_calc_altivec;
         split_radix = 0;
     }
 #endif

     if (split_radix) {
         for(j=4; j<=nbits; j++) {
             int m = 1<<j;
             double freq = 2*M_PI/m;
             FFTSample *tab = ff_cos_tabs[j-4];
             for(i=0; i<=m/4; i++)
                 tab[i] = cos(i*freq);
             for(i=1; i<m/4; i++)
                 tab[m/2-i] = tab[i];
         }
         for(i=0; i<n; i++)
             s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = i;
         s->tmp_buf = av_malloc(n * sizeof(FFTComplex));
     } else {
         int np, nblocks, np2, l;
         FFTComplex *q;

         for(i=0; i<(n/2); i++) {
             alpha = 2 * M_PI * (float)i / (float)n;
             c1 = cos(alpha);
             s1 = sin(alpha) * s2;
             s->exptab[i].re = c1;
             s->exptab[i].im = s1;
         }

         np = 1 << nbits;
         nblocks = np >> 3;
         np2 = np >> 1;
         s->exptab1 = av_malloc(np * 2 * sizeof(FFTComplex));
         if (!s->exptab1)
             goto fail;
         q = s->exptab1;
         do {
             for(l = 0; l < np2; l += 2 * nblocks) {
                 *q++ = s->exptab[l];
                 *q++ = s->exptab[l + nblocks];

                 q->re = -s->exptab[l].im;
                 q->im = s->exptab[l].re;
                 q++;
                 q->re = -s->exptab[l + nblocks].im;
                 q->im = s->exptab[l + nblocks].re;
                 q++;
             }
             nblocks = nblocks >> 1;
         } while (nblocks != 0);
         av_freep(&s->exptab);

         /* compute bit reverse table */
         for(i=0;i<n;i++) {
             m=0;
             for(j=0;j<nbits;j++) {
                 m |= ((i >> j) & 1) << (nbits-j-1);
             }
             s->revtab[i]=m;
         }
     }

     return 0;
  fail:
     av_freep(&s->revtab);
     av_freep(&s->exptab);
     av_freep(&s->exptab1);
     av_freep(&s->tmp_buf);
     return -1;
 }

 void ff_fft_permute_c(FFTContext *s, FFTComplex *z)
 {
     int j, k, np;
     FFTComplex tmp;
     const uint16_t *revtab = s->revtab;
     np = 1 << s->nbits;

     if (s->tmp_buf) {
         /* TODO: handle split-radix permute in a more optimal way, probably in-place */
         for(j=0;j<np;j++) s->tmp_buf[revtab[j]] = z[j];
         memcpy(z, s->tmp_buf, np * sizeof(FFTComplex));
         return;
     }

     /* reverse */
     for(j=0;j<np;j++) {
         k = revtab[j];
         if (k < j) {
             tmp = z[k];
             z[k] = z[j];
             z[j] = tmp;
         }
     }
 }

 av_cold void ff_fft_end(FFTContext *s)
 {
     av_freep(&s->revtab);
     av_freep(&s->exptab);
     av_freep(&s->exptab1);
     av_freep(&s->tmp_buf);
 }

 #define sqrthalf (float)M_SQRT1_2

 #define BF(x,y,a,b) {\
     x = a - b;\
     y = a + b;\
 }

 #define BUTTERFLIES(a0,a1,a2,a3) {\
     BF(t3, t5, t5, t1);\
     BF(a2.re, a0.re, a0.re, t5);\
     BF(a3.im, a1.im, a1.im, t3);\
     BF(t4, t6, t2, t6);\
     BF(a3.re, a1.re, a1.re, t4);\
     BF(a2.im, a0.im, a0.im, t6);\
 }

 // force loading all the inputs before storing any.
 // this is slightly slower for small data, but avoids store->load aliasing
 // for addresses separated by large powers of 2.
 #define BUTTERFLIES_BIG(a0,a1,a2,a3) {\
     FFTSample r0=a0.re, i0=a0.im, r1=a1.re, i1=a1.im;\
     BF(t3, t5, t5, t1);\
     BF(a2.re, a0.re, r0, t5);\
     BF(a3.im, a1.im, i1, t3);\
     BF(t4, t6, t2, t6);\
     BF(a3.re, a1.re, r1, t4);\
     BF(a2.im, a0.im, i0, t6);\
 }

 #define TRANSFORM(a0,a1,a2,a3,wre,wim) {\
     t1 = a2.re * wre + a2.im * wim;\
     t2 = a2.im * wre - a2.re * wim;\
     t5 = a3.re * wre - a3.im * wim;\
     t6 = a3.im * wre + a3.re * wim;\
     BUTTERFLIES(a0,a1,a2,a3)\
 }

 #define TRANSFORM_ZERO(a0,a1,a2,a3) {\
     t1 = a2.re;\
     t2 = a2.im;\
     t5 = a3.re;\
     t6 = a3.im;\
     BUTTERFLIES(a0,a1,a2,a3)\
 }

 /* z[0...8n-1], w[1...2n-1] */
 #define PASS(name)\
 static void name(FFTComplex *z, const FFTSample *wre, unsigned int n)\
 {\
     FFTSample t1, t2, t3, t4, t5, t6;\
     int o1 = 2*n;\
     int o2 = 4*n;\
     int o3 = 6*n;\
     const FFTSample *wim = wre+o1;\
     n--;\
 \
     TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3]);\
     TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
     do {\
         z += 2;\
         wre += 2;\
         wim -= 2;\
         TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0]);\
         TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
     } while(--n);\
 }

 PASS(pass)
 #undef BUTTERFLIES
 #define BUTTERFLIES BUTTERFLIES_BIG
 PASS(pass_big)

 #define DECL_FFT(n,n2,n4)\
 static void fft##n(FFTComplex *z)\
 {\
     fft##n2(z);\
     fft##n4(z+n4*2);\
     fft##n4(z+n4*3);\
     pass(z,ff_cos_##n,n4/2);\
 }

 static void fft4(FFTComplex *z)
 {
     FFTSample t1, t2, t3, t4, t5, t6, t7, t8;

     BF(t3, t1, z[0].re, z[1].re);
     BF(t8, t6, z[3].re, z[2].re);
     BF(z[2].re, z[0].re, t1, t6);
     BF(t4, t2, z[0].im, z[1].im);
     BF(t7, t5, z[2].im, z[3].im);
     BF(z[3].im, z[1].im, t4, t8);
     BF(z[3].re, z[1].re, t3, t7);
     BF(z[2].im, z[0].im, t2, t5);
 }

 static void fft8(FFTComplex *z)
 {
     FFTSample t1, t2, t3, t4, t5, t6, t7, t8;

     fft4(z);

     BF(t1, z[5].re, z[4].re, -z[5].re);
     BF(t2, z[5].im, z[4].im, -z[5].im);
     BF(t3, z[7].re, z[6].re, -z[7].re);
     BF(t4, z[7].im, z[6].im, -z[7].im);
     BF(t8, t1, t3, t1);
     BF(t7, t2, t2, t4);
     BF(z[4].re, z[0].re, z[0].re, t1);
     BF(z[4].im, z[0].im, z[0].im, t2);
     BF(z[6].re, z[2].re, z[2].re, t7);
     BF(z[6].im, z[2].im, z[2].im, t8);

     TRANSFORM(z[1],z[3],z[5],z[7],sqrthalf,sqrthalf);
 }

 #if !CONFIG_SMALL
 static void fft16(FFTComplex *z)
 {
     FFTSample t1, t2, t3, t4, t5, t6;

     fft8(z);
     fft4(z+8);
     fft4(z+12);

     TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
     TRANSFORM(z[2],z[6],z[10],z[14],sqrthalf,sqrthalf);
     TRANSFORM(z[1],z[5],z[9],z[13],ff_cos_16[1],ff_cos_16[3]);
     TRANSFORM(z[3],z[7],z[11],z[15],ff_cos_16[3],ff_cos_16[1]);
 }
 #else
 DECL_FFT(16,8,4)
 #endif
 DECL_FFT(32,16,8)
 DECL_FFT(64,32,16)
 DECL_FFT(128,64,32)
 DECL_FFT(256,128,64)
 DECL_FFT(512,256,128)
 #if !CONFIG_SMALL
 #define pass pass_big
 #endif
 DECL_FFT(1024,512,256)
 DECL_FFT(2048,1024,512)
 DECL_FFT(4096,2048,1024)
 DECL_FFT(8192,4096,2048)
 DECL_FFT(16384,8192,4096)
 DECL_FFT(32768,16384,8192)
 DECL_FFT(65536,32768,16384)

 static void (*fft_dispatch[])(FFTComplex*) = {
     fft4, fft8, fft16, fft32, fft64, fft128, fft256, fft512, fft1024,
     fft2048, fft4096, fft8192, fft16384, fft32768, fft65536,
 };

 void ff_fft_calc_c(FFTContext *s, FFTComplex *z)
 {
     fft_dispatch[s->nbits-2](z);
 }
	/*
	* FFT/IFFT transforms
	* Copyright (c) 2008 Loren Merritt
	* Copyright (c) 2002 Fabrice Bellard
	* Partly based on libdjbfft by D. J. Bernstein
	*
	* This file is part of FFmpeg.
	*
	* FFmpeg is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* FFmpeg is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with FFmpeg; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	/**
	* @file libavcodec/fft.c
	* FFT/IFFT transforms.
	*/

	#include "dsputil.h"

	/* cos(2pix/n) for 0<=x<=n/4, followed by its reverse */
	DECLARE_ALIGNED_16(FFTSample, ff_cos_16[8]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_32[16]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_64[32]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_128[64]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_256[128]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_512[256]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_1024[512]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_2048[1024]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_4096[2048]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_8192[4096]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_16384[8192]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_32768[16384]);
	DECLARE_ALIGNED_16(FFTSample, ff_cos_65536[32768]);
	FFTSample *ff_cos_tabs[] = {
	ff_cos_16, ff_cos_32, ff_cos_64, ff_cos_128, ff_cos_256, ff_cos_512, ff_cos_1024,
	ff_cos_2048, ff_cos_4096, ff_cos_8192, ff_cos_16384, ff_cos_32768, ff_cos_65536,
	};

	static int split_radix_permutation(int i, int n, int inverse)
	{
	int m;
	if(n <= 2) return i&1;
	m = n >> 1;
	if(!(i&m)) return split_radix_permutation(i, m, inverse)*2;
	m >>= 1;
	if(inverse == !(i&m)) return split_radix_permutation(i, m, inverse)*4 + 1;
	else return split_radix_permutation(i, m, inverse)*4 - 1;
	}

	av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
	{
	int i, j, m, n;
	float alpha, c1, s1, s2;
	int split_radix = 1;
	int av_unused has_vectors;

	if (nbits < 2 \|\| nbits > 16)
	goto fail;
	s->nbits = nbits;
	n = 1 << nbits;

	s->tmp_buf = NULL;
	s->exptab = av_malloc((n / 2) * sizeof(FFTComplex));
	if (!s->exptab)
	goto fail;
	s->revtab = av_malloc(n * sizeof(uint16_t));
	if (!s->revtab)
	goto fail;
	s->inverse = inverse;

	s2 = inverse ? 1.0 : -1.0;

	s->fft_permute = ff_fft_permute_c;
	s->fft_calc = ff_fft_calc_c;
	s->imdct_calc = ff_imdct_calc_c;
	s->imdct_half = ff_imdct_half_c;
	s->exptab1 = NULL;

	#if HAVE_MMX && HAVE_YASM
	has_vectors = mm_support();
	if (has_vectors & FF_MM_SSE && HAVE_SSE) {
	/* SSE for P3/P4/K8 */
	s->imdct_calc = ff_imdct_calc_sse;
	s->imdct_half = ff_imdct_half_sse;
	s->fft_permute = ff_fft_permute_sse;
	s->fft_calc = ff_fft_calc_sse;
	} else if (has_vectors & FF_MM_3DNOWEXT && HAVE_AMD3DNOWEXT) {
	/* 3DNowEx for K7 */
	s->imdct_calc = ff_imdct_calc_3dn2;
	s->imdct_half = ff_imdct_half_3dn2;
	s->fft_calc = ff_fft_calc_3dn2;
	} else if (has_vectors & FF_MM_3DNOW && HAVE_AMD3DNOW) {
	/* 3DNow! for K6-2/3 */
	s->imdct_calc = ff_imdct_calc_3dn;
	s->imdct_half = ff_imdct_half_3dn;
	s->fft_calc = ff_fft_calc_3dn;
	}
	#elif HAVE_ALTIVEC
	has_vectors = mm_support();
	if (has_vectors & FF_MM_ALTIVEC) {
	s->fft_calc = ff_fft_calc_altivec;
	split_radix = 0;
	}
	#endif

	if (split_radix) {
	for(j=4; j<=nbits; j++) {
	int m = 1<<j;
	double freq = 2*M_PI/m;
	FFTSample *tab = ff_cos_tabs[j-4];
	for(i=0; i<=m/4; i++)
	tab[i] = cos(i*freq);
	for(i=1; i<m/4; i++)
	tab[m/2-i] = tab[i];
	}
	for(i=0; i<n; i++)
	s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = i;
	s->tmp_buf = av_malloc(n * sizeof(FFTComplex));
	} else {
	int np, nblocks, np2, l;
	FFTComplex *q;

	for(i=0; i<(n/2); i++) {
	alpha = 2 * M_PI * (float)i / (float)n;
	c1 = cos(alpha);
	s1 = sin(alpha) * s2;
	s->exptab[i].re = c1;
	s->exptab[i].im = s1;
	}

	np = 1 << nbits;
	nblocks = np >> 3;
	np2 = np >> 1;
	s->exptab1 = av_malloc(np * 2 * sizeof(FFTComplex));
	if (!s->exptab1)
	goto fail;
	q = s->exptab1;
	do {
	for(l = 0; l < np2; l += 2 * nblocks) {
	*q++ = s->exptab[l];
	*q++ = s->exptab[l + nblocks];

	q->re = -s->exptab[l].im;
	q->im = s->exptab[l].re;
	q++;
	q->re = -s->exptab[l + nblocks].im;
	q->im = s->exptab[l + nblocks].re;
	q++;
	}
	nblocks = nblocks >> 1;
	} while (nblocks != 0);
	av_freep(&s->exptab);

	/* compute bit reverse table */
	for(i=0;i<n;i++) {
	m=0;
	for(j=0;j<nbits;j++) {
	m \|= ((i >> j) & 1) << (nbits-j-1);
	}
	s->revtab[i]=m;
	}
	}

	return 0;
	fail:
	av_freep(&s->revtab);
	av_freep(&s->exptab);
	av_freep(&s->exptab1);
	av_freep(&s->tmp_buf);
	return -1;
	}

	void ff_fft_permute_c(FFTContext s, FFTComplex z)
	{
	int j, k, np;
	FFTComplex tmp;
	const uint16_t *revtab = s->revtab;
	np = 1 << s->nbits;

	if (s->tmp_buf) {
	/* TODO: handle split-radix permute in a more optimal way, probably in-place */
	for(j=0;j<np;j++) s->tmp_buf[revtab[j]] = z[j];
	memcpy(z, s->tmp_buf, np * sizeof(FFTComplex));
	return;
	}

	/* reverse */
	for(j=0;j<np;j++) {
	k = revtab[j];
	if (k < j) {
	tmp = z[k];
	z[k] = z[j];
	z[j] = tmp;
	}
	}
	}

	av_cold void ff_fft_end(FFTContext *s)
	{
	av_freep(&s->revtab);
	av_freep(&s->exptab);
	av_freep(&s->exptab1);
	av_freep(&s->tmp_buf);
	}

	#define sqrthalf (float)M_SQRT1_2

	#define BF(x,y,a,b) {\
	x = a - b;\
	y = a + b;\
	}

	#define BUTTERFLIES(a0,a1,a2,a3) {\
	BF(t3, t5, t5, t1);\
	BF(a2.re, a0.re, a0.re, t5);\
	BF(a3.im, a1.im, a1.im, t3);\
	BF(t4, t6, t2, t6);\
	BF(a3.re, a1.re, a1.re, t4);\
	BF(a2.im, a0.im, a0.im, t6);\
	}

	// force loading all the inputs before storing any.
	// this is slightly slower for small data, but avoids store->load aliasing
	// for addresses separated by large powers of 2.
	#define BUTTERFLIES_BIG(a0,a1,a2,a3) {\
	FFTSample r0=a0.re, i0=a0.im, r1=a1.re, i1=a1.im;\
	BF(t3, t5, t5, t1);\
	BF(a2.re, a0.re, r0, t5);\
	BF(a3.im, a1.im, i1, t3);\
	BF(t4, t6, t2, t6);\
	BF(a3.re, a1.re, r1, t4);\
	BF(a2.im, a0.im, i0, t6);\
	}

	#define TRANSFORM(a0,a1,a2,a3,wre,wim) {\
	t1 = a2.re * wre + a2.im * wim;\
	t2 = a2.im * wre - a2.re * wim;\
	t5 = a3.re * wre - a3.im * wim;\
	t6 = a3.im * wre + a3.re * wim;\
	BUTTERFLIES(a0,a1,a2,a3)\
	}

	#define TRANSFORM_ZERO(a0,a1,a2,a3) {\
	t1 = a2.re;\
	t2 = a2.im;\
	t5 = a3.re;\
	t6 = a3.im;\
	BUTTERFLIES(a0,a1,a2,a3)\
	}

	/* z[0...8n-1], w[1...2n-1] */
	#define PASS(name)\
	static void name(FFTComplex z, const FFTSample wre, unsigned int n)\
	{\
	FFTSample t1, t2, t3, t4, t5, t6;\
	int o1 = 2*n;\
	int o2 = 4*n;\
	int o3 = 6*n;\
	const FFTSample *wim = wre+o1;\
	n--;\
	\
	TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3]);\
	TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
	do {\
	z += 2;\
	wre += 2;\
	wim -= 2;\
	TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0]);\
	TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
	} while(--n);\
	}

	PASS(pass)
	#undef BUTTERFLIES
	#define BUTTERFLIES BUTTERFLIES_BIG
	PASS(pass_big)

	#define DECL_FFT(n,n2,n4)\
	static void fft##n(FFTComplex *z)\
	{\
	fft##n2(z);\
	fft##n4(z+n4*2);\
	fft##n4(z+n4*3);\
	pass(z,ff_cos_##n,n4/2);\
	}

	static void fft4(FFTComplex *z)
	{
	FFTSample t1, t2, t3, t4, t5, t6, t7, t8;

	BF(t3, t1, z[0].re, z[1].re);
	BF(t8, t6, z[3].re, z[2].re);
	BF(z[2].re, z[0].re, t1, t6);
	BF(t4, t2, z[0].im, z[1].im);
	BF(t7, t5, z[2].im, z[3].im);
	BF(z[3].im, z[1].im, t4, t8);
	BF(z[3].re, z[1].re, t3, t7);
	BF(z[2].im, z[0].im, t2, t5);
	}

	static void fft8(FFTComplex *z)
	{
	FFTSample t1, t2, t3, t4, t5, t6, t7, t8;

	fft4(z);

	BF(t1, z[5].re, z[4].re, -z[5].re);
	BF(t2, z[5].im, z[4].im, -z[5].im);
	BF(t3, z[7].re, z[6].re, -z[7].re);
	BF(t4, z[7].im, z[6].im, -z[7].im);
	BF(t8, t1, t3, t1);
	BF(t7, t2, t2, t4);
	BF(z[4].re, z[0].re, z[0].re, t1);
	BF(z[4].im, z[0].im, z[0].im, t2);
	BF(z[6].re, z[2].re, z[2].re, t7);
	BF(z[6].im, z[2].im, z[2].im, t8);

	TRANSFORM(z[1],z[3],z[5],z[7],sqrthalf,sqrthalf);
	}

	#if !CONFIG_SMALL
	static void fft16(FFTComplex *z)
	{
	FFTSample t1, t2, t3, t4, t5, t6;

	fft8(z);
	fft4(z+8);
	fft4(z+12);

	TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
	TRANSFORM(z[2],z[6],z[10],z[14],sqrthalf,sqrthalf);
	TRANSFORM(z[1],z[5],z[9],z[13],ff_cos_16[1],ff_cos_16[3]);
	TRANSFORM(z[3],z[7],z[11],z[15],ff_cos_16[3],ff_cos_16[1]);
	}
	#else
	DECL_FFT(16,8,4)
	#endif
	DECL_FFT(32,16,8)
	DECL_FFT(64,32,16)
	DECL_FFT(128,64,32)
	DECL_FFT(256,128,64)
	DECL_FFT(512,256,128)
	#if !CONFIG_SMALL
	#define pass pass_big
	#endif
	DECL_FFT(1024,512,256)
	DECL_FFT(2048,1024,512)
	DECL_FFT(4096,2048,1024)
	DECL_FFT(8192,4096,2048)
	DECL_FFT(16384,8192,4096)
	DECL_FFT(32768,16384,8192)
	DECL_FFT(65536,32768,16384)

	static void (fft_dispatch[])(FFTComplex) = {
	fft4, fft8, fft16, fft32, fft64, fft128, fft256, fft512, fft1024,
	fft2048, fft4096, fft8192, fft16384, fft32768, fft65536,
	};

	void ff_fft_calc_c(FFTContext s, FFTComplex z)
	{
	fft_dispatch[s->nbits-2](z);
	}