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  1. /*
  2.  * FFT/IFFT transforms
  3.  * Copyright (c) 2008 Loren Merritt
  4.  * Copyright (c) 2002 Fabrice Bellard
  5.  * Partly based on libdjbfft by D. J. Bernstein
  6.  *
  7.  * This file is part of FFmpeg.
  8.  *
  9.  * FFmpeg is free software; you can redistribute it and/or
  10.  * modify it under the terms of the GNU Lesser General Public
  11.  * License as published by the Free Software Foundation; either
  12.  * version 2.1 of the License, or (at your option) any later version.
  13.  *
  14.  * FFmpeg is distributed in the hope that it will be useful,
  15.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17.  * Lesser General Public License for more details.
  18.  *
  19.  * You should have received a copy of the GNU Lesser General Public
  20.  * License along with FFmpeg; if not, write to the Free Software
  21.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22.  */
  23.  
  24. /**
  25.  * @file
  26.  * FFT/IFFT transforms.
  27.  */
  28.  
  29. #include <stdlib.h>
  30. #include <string.h>
  31. #include "libavutil/mathematics.h"
  32. #include "fft.h"
  33. #include "fft-internal.h"
  34.  
  35. #if FFT_FIXED_32
  36. #include "fft_table.h"
  37. #else /* FFT_FIXED_32 */
  38.  
  39. /* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
  40. #if !CONFIG_HARDCODED_TABLES
  41. COSTABLE(16);
  42. COSTABLE(32);
  43. COSTABLE(64);
  44. COSTABLE(128);
  45. COSTABLE(256);
  46. COSTABLE(512);
  47. COSTABLE(1024);
  48. COSTABLE(2048);
  49. COSTABLE(4096);
  50. COSTABLE(8192);
  51. COSTABLE(16384);
  52. COSTABLE(32768);
  53. COSTABLE(65536);
  54. #endif
  55. COSTABLE_CONST FFTSample * const FFT_NAME(ff_cos_tabs)[] = {
  56.     NULL, NULL, NULL, NULL,
  57.     FFT_NAME(ff_cos_16),
  58.     FFT_NAME(ff_cos_32),
  59.     FFT_NAME(ff_cos_64),
  60.     FFT_NAME(ff_cos_128),
  61.     FFT_NAME(ff_cos_256),
  62.     FFT_NAME(ff_cos_512),
  63.     FFT_NAME(ff_cos_1024),
  64.     FFT_NAME(ff_cos_2048),
  65.     FFT_NAME(ff_cos_4096),
  66.     FFT_NAME(ff_cos_8192),
  67.     FFT_NAME(ff_cos_16384),
  68.     FFT_NAME(ff_cos_32768),
  69.     FFT_NAME(ff_cos_65536),
  70. };
  71.  
  72. #endif /* FFT_FIXED_32 */
  73.  
  74. static void fft_permute_c(FFTContext *s, FFTComplex *z);
  75. static void fft_calc_c(FFTContext *s, FFTComplex *z);
  76.  
  77. static int split_radix_permutation(int i, int n, int inverse)
  78. {
  79.     int m;
  80.     if(n <= 2) return i&1;
  81.     m = n >> 1;
  82.     if(!(i&m))            return split_radix_permutation(i, m, inverse)*2;
  83.     m >>= 1;
  84.     if(inverse == !(i&m)) return split_radix_permutation(i, m, inverse)*4 + 1;
  85.     else                  return split_radix_permutation(i, m, inverse)*4 - 1;
  86. }
  87.  
  88. av_cold void ff_init_ff_cos_tabs(int index)
  89. {
  90. #if (!CONFIG_HARDCODED_TABLES) && (!FFT_FIXED_32)
  91.     int i;
  92.     int m = 1<<index;
  93.     double freq = 2*M_PI/m;
  94.     FFTSample *tab = FFT_NAME(ff_cos_tabs)[index];
  95.     for(i=0; i<=m/4; i++)
  96.         tab[i] = FIX15(cos(i*freq));
  97.     for(i=1; i<m/4; i++)
  98.         tab[m/2-i] = tab[i];
  99. #endif
  100. }
  101.  
  102. static const int avx_tab[] = {
  103.     0, 4, 1, 5, 8, 12, 9, 13, 2, 6, 3, 7, 10, 14, 11, 15
  104. };
  105.  
  106. static int is_second_half_of_fft32(int i, int n)
  107. {
  108.     if (n <= 32)
  109.         return i >= 16;
  110.     else if (i < n/2)
  111.         return is_second_half_of_fft32(i, n/2);
  112.     else if (i < 3*n/4)
  113.         return is_second_half_of_fft32(i - n/2, n/4);
  114.     else
  115.         return is_second_half_of_fft32(i - 3*n/4, n/4);
  116. }
  117.  
  118. static av_cold void fft_perm_avx(FFTContext *s)
  119. {
  120.     int i;
  121.     int n = 1 << s->nbits;
  122.  
  123.     for (i = 0; i < n; i += 16) {
  124.         int k;
  125.         if (is_second_half_of_fft32(i, n)) {
  126.             for (k = 0; k < 16; k++)
  127.                 s->revtab[-split_radix_permutation(i + k, n, s->inverse) & (n - 1)] =
  128.                     i + avx_tab[k];
  129.  
  130.         } else {
  131.             for (k = 0; k < 16; k++) {
  132.                 int j = i + k;
  133.                 j = (j & ~7) | ((j >> 1) & 3) | ((j << 2) & 4);
  134.                 s->revtab[-split_radix_permutation(i + k, n, s->inverse) & (n - 1)] = j;
  135.             }
  136.         }
  137.     }
  138. }
  139.  
  140. av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
  141. {
  142.     int i, j, n;
  143.  
  144.     if (nbits < 2 || nbits > 16)
  145.         goto fail;
  146.     s->nbits = nbits;
  147.     n = 1 << nbits;
  148.  
  149.     s->revtab = av_malloc(n * sizeof(uint16_t));
  150.     if (!s->revtab)
  151.         goto fail;
  152.     s->tmp_buf = av_malloc(n * sizeof(FFTComplex));
  153.     if (!s->tmp_buf)
  154.         goto fail;
  155.     s->inverse = inverse;
  156.     s->fft_permutation = FF_FFT_PERM_DEFAULT;
  157.  
  158.     s->fft_permute = fft_permute_c;
  159.     s->fft_calc    = fft_calc_c;
  160. #if CONFIG_MDCT
  161.     s->imdct_calc  = ff_imdct_calc_c;
  162.     s->imdct_half  = ff_imdct_half_c;
  163.     s->mdct_calc   = ff_mdct_calc_c;
  164. #endif
  165.  
  166. #if FFT_FIXED_32
  167.     {
  168.         int n=0;
  169.         ff_fft_lut_init(ff_fft_offsets_lut, 0, 1 << 16, &n);
  170.     }
  171. #else /* FFT_FIXED_32 */
  172. #if FFT_FLOAT
  173.     if (ARCH_AARCH64) ff_fft_init_aarch64(s);
  174.     if (ARCH_ARM)     ff_fft_init_arm(s);
  175.     if (ARCH_PPC)     ff_fft_init_ppc(s);
  176.     if (ARCH_X86)     ff_fft_init_x86(s);
  177.     if (CONFIG_MDCT)  s->mdct_calcw = s->mdct_calc;
  178.     if (HAVE_MIPSFPU) ff_fft_init_mips(s);
  179. #else
  180.     if (CONFIG_MDCT)  s->mdct_calcw = ff_mdct_calcw_c;
  181.     if (ARCH_ARM)     ff_fft_fixed_init_arm(s);
  182. #endif
  183.     for(j=4; j<=nbits; j++) {
  184.         ff_init_ff_cos_tabs(j);
  185.     }
  186. #endif /* FFT_FIXED_32 */
  187.  
  188.  
  189.     if (s->fft_permutation == FF_FFT_PERM_AVX) {
  190.         fft_perm_avx(s);
  191.     } else {
  192.         for(i=0; i<n; i++) {
  193.             j = i;
  194.             if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS)
  195.                 j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);
  196.             s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = j;
  197.         }
  198.     }
  199.  
  200.     return 0;
  201.  fail:
  202.     av_freep(&s->revtab);
  203.     av_freep(&s->tmp_buf);
  204.     return -1;
  205. }
  206.  
  207. static void fft_permute_c(FFTContext *s, FFTComplex *z)
  208. {
  209.     int j, np;
  210.     const uint16_t *revtab = s->revtab;
  211.     np = 1 << s->nbits;
  212.     /* TODO: handle split-radix permute in a more optimal way, probably in-place */
  213.     for(j=0;j<np;j++) s->tmp_buf[revtab[j]] = z[j];
  214.     memcpy(z, s->tmp_buf, np * sizeof(FFTComplex));
  215. }
  216.  
  217. av_cold void ff_fft_end(FFTContext *s)
  218. {
  219.     av_freep(&s->revtab);
  220.     av_freep(&s->tmp_buf);
  221. }
  222.  
  223. #if FFT_FIXED_32
  224.  
  225. static void fft_calc_c(FFTContext *s, FFTComplex *z) {
  226.  
  227.     int nbits, i, n, num_transforms, offset, step;
  228.     int n4, n2, n34;
  229.     FFTSample tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7, tmp8;
  230.     FFTComplex *tmpz;
  231.     const int fft_size = (1 << s->nbits);
  232.     int64_t accu;
  233.  
  234.     num_transforms = (0x2aab >> (16 - s->nbits)) | 1;
  235.  
  236.     for (n=0; n<num_transforms; n++){
  237.         offset = ff_fft_offsets_lut[n] << 2;
  238.         tmpz = z + offset;
  239.  
  240.         tmp1 = tmpz[0].re + tmpz[1].re;
  241.         tmp5 = tmpz[2].re + tmpz[3].re;
  242.         tmp2 = tmpz[0].im + tmpz[1].im;
  243.         tmp6 = tmpz[2].im + tmpz[3].im;
  244.         tmp3 = tmpz[0].re - tmpz[1].re;
  245.         tmp8 = tmpz[2].im - tmpz[3].im;
  246.         tmp4 = tmpz[0].im - tmpz[1].im;
  247.         tmp7 = tmpz[2].re - tmpz[3].re;
  248.  
  249.         tmpz[0].re = tmp1 + tmp5;
  250.         tmpz[2].re = tmp1 - tmp5;
  251.         tmpz[0].im = tmp2 + tmp6;
  252.         tmpz[2].im = tmp2 - tmp6;
  253.         tmpz[1].re = tmp3 + tmp8;
  254.         tmpz[3].re = tmp3 - tmp8;
  255.         tmpz[1].im = tmp4 - tmp7;
  256.         tmpz[3].im = tmp4 + tmp7;
  257.     }
  258.  
  259.     if (fft_size < 8)
  260.         return;
  261.  
  262.     num_transforms = (num_transforms >> 1) | 1;
  263.  
  264.     for (n=0; n<num_transforms; n++){
  265.         offset = ff_fft_offsets_lut[n] << 3;
  266.         tmpz = z + offset;
  267.  
  268.         tmp1 = tmpz[4].re + tmpz[5].re;
  269.         tmp3 = tmpz[6].re + tmpz[7].re;
  270.         tmp2 = tmpz[4].im + tmpz[5].im;
  271.         tmp4 = tmpz[6].im + tmpz[7].im;
  272.         tmp5 = tmp1 + tmp3;
  273.         tmp7 = tmp1 - tmp3;
  274.         tmp6 = tmp2 + tmp4;
  275.         tmp8 = tmp2 - tmp4;
  276.  
  277.         tmp1 = tmpz[4].re - tmpz[5].re;
  278.         tmp2 = tmpz[4].im - tmpz[5].im;
  279.         tmp3 = tmpz[6].re - tmpz[7].re;
  280.         tmp4 = tmpz[6].im - tmpz[7].im;
  281.  
  282.         tmpz[4].re = tmpz[0].re - tmp5;
  283.         tmpz[0].re = tmpz[0].re + tmp5;
  284.         tmpz[4].im = tmpz[0].im - tmp6;
  285.         tmpz[0].im = tmpz[0].im + tmp6;
  286.         tmpz[6].re = tmpz[2].re - tmp8;
  287.         tmpz[2].re = tmpz[2].re + tmp8;
  288.         tmpz[6].im = tmpz[2].im + tmp7;
  289.         tmpz[2].im = tmpz[2].im - tmp7;
  290.  
  291.         accu = (int64_t)Q31(M_SQRT1_2)*(tmp1 + tmp2);
  292.         tmp5 = (int32_t)((accu + 0x40000000) >> 31);
  293.         accu = (int64_t)Q31(M_SQRT1_2)*(tmp3 - tmp4);
  294.         tmp7 = (int32_t)((accu + 0x40000000) >> 31);
  295.         accu = (int64_t)Q31(M_SQRT1_2)*(tmp2 - tmp1);
  296.         tmp6 = (int32_t)((accu + 0x40000000) >> 31);
  297.         accu = (int64_t)Q31(M_SQRT1_2)*(tmp3 + tmp4);
  298.         tmp8 = (int32_t)((accu + 0x40000000) >> 31);
  299.         tmp1 = tmp5 + tmp7;
  300.         tmp3 = tmp5 - tmp7;
  301.         tmp2 = tmp6 + tmp8;
  302.         tmp4 = tmp6 - tmp8;
  303.  
  304.         tmpz[5].re = tmpz[1].re - tmp1;
  305.         tmpz[1].re = tmpz[1].re + tmp1;
  306.         tmpz[5].im = tmpz[1].im - tmp2;
  307.         tmpz[1].im = tmpz[1].im + tmp2;
  308.         tmpz[7].re = tmpz[3].re - tmp4;
  309.         tmpz[3].re = tmpz[3].re + tmp4;
  310.         tmpz[7].im = tmpz[3].im + tmp3;
  311.         tmpz[3].im = tmpz[3].im - tmp3;
  312.     }
  313.  
  314.     step = 1 << ((MAX_LOG2_NFFT-4) - 4);
  315.     n4 = 4;
  316.  
  317.     for (nbits=4; nbits<=s->nbits; nbits++){
  318.         n2  = 2*n4;
  319.         n34 = 3*n4;
  320.         num_transforms = (num_transforms >> 1) | 1;
  321.  
  322.         for (n=0; n<num_transforms; n++){
  323.             const FFTSample *w_re_ptr = ff_w_tab_sr + step;
  324.             const FFTSample *w_im_ptr = ff_w_tab_sr + MAX_FFT_SIZE/(4*16) - step;
  325.             offset = ff_fft_offsets_lut[n] << nbits;
  326.             tmpz = z + offset;
  327.  
  328.             tmp5 = tmpz[ n2].re + tmpz[n34].re;
  329.             tmp1 = tmpz[ n2].re - tmpz[n34].re;
  330.             tmp6 = tmpz[ n2].im + tmpz[n34].im;
  331.             tmp2 = tmpz[ n2].im - tmpz[n34].im;
  332.  
  333.             tmpz[ n2].re = tmpz[ 0].re - tmp5;
  334.             tmpz[  0].re = tmpz[ 0].re + tmp5;
  335.             tmpz[ n2].im = tmpz[ 0].im - tmp6;
  336.             tmpz[  0].im = tmpz[ 0].im + tmp6;
  337.             tmpz[n34].re = tmpz[n4].re - tmp2;
  338.             tmpz[ n4].re = tmpz[n4].re + tmp2;
  339.             tmpz[n34].im = tmpz[n4].im + tmp1;
  340.             tmpz[ n4].im = tmpz[n4].im - tmp1;
  341.  
  342.             for (i=1; i<n4; i++){
  343.                 FFTSample w_re = w_re_ptr[0];
  344.                 FFTSample w_im = w_im_ptr[0];
  345.                 accu  = (int64_t)w_re*tmpz[ n2+i].re;
  346.                 accu += (int64_t)w_im*tmpz[ n2+i].im;
  347.                 tmp1 = (int32_t)((accu + 0x40000000) >> 31);
  348.                 accu  = (int64_t)w_re*tmpz[ n2+i].im;
  349.                 accu -= (int64_t)w_im*tmpz[ n2+i].re;
  350.                 tmp2 = (int32_t)((accu + 0x40000000) >> 31);
  351.                 accu  = (int64_t)w_re*tmpz[n34+i].re;
  352.                 accu -= (int64_t)w_im*tmpz[n34+i].im;
  353.                 tmp3 = (int32_t)((accu + 0x40000000) >> 31);
  354.                 accu  = (int64_t)w_re*tmpz[n34+i].im;
  355.                 accu += (int64_t)w_im*tmpz[n34+i].re;
  356.                 tmp4 = (int32_t)((accu + 0x40000000) >> 31);
  357.  
  358.                 tmp5 = tmp1 + tmp3;
  359.                 tmp1 = tmp1 - tmp3;
  360.                 tmp6 = tmp2 + tmp4;
  361.                 tmp2 = tmp2 - tmp4;
  362.  
  363.                 tmpz[ n2+i].re = tmpz[   i].re - tmp5;
  364.                 tmpz[    i].re = tmpz[   i].re + tmp5;
  365.                 tmpz[ n2+i].im = tmpz[   i].im - tmp6;
  366.                 tmpz[    i].im = tmpz[   i].im + tmp6;
  367.                 tmpz[n34+i].re = tmpz[n4+i].re - tmp2;
  368.                 tmpz[ n4+i].re = tmpz[n4+i].re + tmp2;
  369.                 tmpz[n34+i].im = tmpz[n4+i].im + tmp1;
  370.                 tmpz[ n4+i].im = tmpz[n4+i].im - tmp1;
  371.  
  372.                 w_re_ptr += step;
  373.                 w_im_ptr -= step;
  374.             }
  375.         }
  376.         step >>= 1;
  377.         n4   <<= 1;
  378.     }
  379. }
  380.  
  381. #else /* FFT_FIXED_32 */
  382.  
  383. #define BUTTERFLIES(a0,a1,a2,a3) {\
  384.     BF(t3, t5, t5, t1);\
  385.     BF(a2.re, a0.re, a0.re, t5);\
  386.     BF(a3.im, a1.im, a1.im, t3);\
  387.     BF(t4, t6, t2, t6);\
  388.     BF(a3.re, a1.re, a1.re, t4);\
  389.     BF(a2.im, a0.im, a0.im, t6);\
  390. }
  391.  
  392. // force loading all the inputs before storing any.
  393. // this is slightly slower for small data, but avoids store->load aliasing
  394. // for addresses separated by large powers of 2.
  395. #define BUTTERFLIES_BIG(a0,a1,a2,a3) {\
  396.     FFTSample r0=a0.re, i0=a0.im, r1=a1.re, i1=a1.im;\
  397.     BF(t3, t5, t5, t1);\
  398.     BF(a2.re, a0.re, r0, t5);\
  399.     BF(a3.im, a1.im, i1, t3);\
  400.     BF(t4, t6, t2, t6);\
  401.     BF(a3.re, a1.re, r1, t4);\
  402.     BF(a2.im, a0.im, i0, t6);\
  403. }
  404.  
  405. #define TRANSFORM(a0,a1,a2,a3,wre,wim) {\
  406.     CMUL(t1, t2, a2.re, a2.im, wre, -wim);\
  407.     CMUL(t5, t6, a3.re, a3.im, wre,  wim);\
  408.     BUTTERFLIES(a0,a1,a2,a3)\
  409. }
  410.  
  411. #define TRANSFORM_ZERO(a0,a1,a2,a3) {\
  412.     t1 = a2.re;\
  413.     t2 = a2.im;\
  414.     t5 = a3.re;\
  415.     t6 = a3.im;\
  416.     BUTTERFLIES(a0,a1,a2,a3)\
  417. }
  418.  
  419. /* z[0...8n-1], w[1...2n-1] */
  420. #define PASS(name)\
  421. static void name(FFTComplex *z, const FFTSample *wre, unsigned int n)\
  422. {\
  423.     FFTDouble t1, t2, t3, t4, t5, t6;\
  424.     int o1 = 2*n;\
  425.     int o2 = 4*n;\
  426.     int o3 = 6*n;\
  427.     const FFTSample *wim = wre+o1;\
  428.     n--;\
  429. \
  430.     TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3]);\
  431.     TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
  432.     do {\
  433.         z += 2;\
  434.         wre += 2;\
  435.         wim -= 2;\
  436.         TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0]);\
  437.         TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
  438.     } while(--n);\
  439. }
  440.  
  441. PASS(pass)
  442. #undef BUTTERFLIES
  443. #define BUTTERFLIES BUTTERFLIES_BIG
  444. PASS(pass_big)
  445.  
  446. #define DECL_FFT(n,n2,n4)\
  447. static void fft##n(FFTComplex *z)\
  448. {\
  449.     fft##n2(z);\
  450.     fft##n4(z+n4*2);\
  451.     fft##n4(z+n4*3);\
  452.     pass(z,FFT_NAME(ff_cos_##n),n4/2);\
  453. }
  454.  
  455. static void fft4(FFTComplex *z)
  456. {
  457.     FFTDouble t1, t2, t3, t4, t5, t6, t7, t8;
  458.  
  459.     BF(t3, t1, z[0].re, z[1].re);
  460.     BF(t8, t6, z[3].re, z[2].re);
  461.     BF(z[2].re, z[0].re, t1, t6);
  462.     BF(t4, t2, z[0].im, z[1].im);
  463.     BF(t7, t5, z[2].im, z[3].im);
  464.     BF(z[3].im, z[1].im, t4, t8);
  465.     BF(z[3].re, z[1].re, t3, t7);
  466.     BF(z[2].im, z[0].im, t2, t5);
  467. }
  468.  
  469. static void fft8(FFTComplex *z)
  470. {
  471.     FFTDouble t1, t2, t3, t4, t5, t6;
  472.  
  473.     fft4(z);
  474.  
  475.     BF(t1, z[5].re, z[4].re, -z[5].re);
  476.     BF(t2, z[5].im, z[4].im, -z[5].im);
  477.     BF(t5, z[7].re, z[6].re, -z[7].re);
  478.     BF(t6, z[7].im, z[6].im, -z[7].im);
  479.  
  480.     BUTTERFLIES(z[0],z[2],z[4],z[6]);
  481.     TRANSFORM(z[1],z[3],z[5],z[7],sqrthalf,sqrthalf);
  482. }
  483.  
  484. #if !CONFIG_SMALL
  485. static void fft16(FFTComplex *z)
  486. {
  487.     FFTDouble t1, t2, t3, t4, t5, t6;
  488.     FFTSample cos_16_1 = FFT_NAME(ff_cos_16)[1];
  489.     FFTSample cos_16_3 = FFT_NAME(ff_cos_16)[3];
  490.  
  491.     fft8(z);
  492.     fft4(z+8);
  493.     fft4(z+12);
  494.  
  495.     TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
  496.     TRANSFORM(z[2],z[6],z[10],z[14],sqrthalf,sqrthalf);
  497.     TRANSFORM(z[1],z[5],z[9],z[13],cos_16_1,cos_16_3);
  498.     TRANSFORM(z[3],z[7],z[11],z[15],cos_16_3,cos_16_1);
  499. }
  500. #else
  501. DECL_FFT(16,8,4)
  502. #endif
  503. DECL_FFT(32,16,8)
  504. DECL_FFT(64,32,16)
  505. DECL_FFT(128,64,32)
  506. DECL_FFT(256,128,64)
  507. DECL_FFT(512,256,128)
  508. #if !CONFIG_SMALL
  509. #define pass pass_big
  510. #endif
  511. DECL_FFT(1024,512,256)
  512. DECL_FFT(2048,1024,512)
  513. DECL_FFT(4096,2048,1024)
  514. DECL_FFT(8192,4096,2048)
  515. DECL_FFT(16384,8192,4096)
  516. DECL_FFT(32768,16384,8192)
  517. DECL_FFT(65536,32768,16384)
  518.  
  519. static void (* const fft_dispatch[])(FFTComplex*) = {
  520.     fft4, fft8, fft16, fft32, fft64, fft128, fft256, fft512, fft1024,
  521.     fft2048, fft4096, fft8192, fft16384, fft32768, fft65536,
  522. };
  523.  
  524. static void fft_calc_c(FFTContext *s, FFTComplex *z)
  525. {
  526.     fft_dispatch[s->nbits-2](z);
  527. }
  528. #endif /* FFT_FIXED_32 */
  529.