libavutil/tx_template.c
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 /*
  * Copyright (c) 2019 Lynne <dev@lynne.ee>
  * Power of two FFT:
  * 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
  */
 
 /* All costabs for a type are defined here */
 COSTABLE(16);
 COSTABLE(32);
 COSTABLE(64);
 COSTABLE(128);
 COSTABLE(256);
 COSTABLE(512);
 COSTABLE(1024);
 COSTABLE(2048);
 COSTABLE(4096);
 COSTABLE(8192);
 COSTABLE(16384);
 COSTABLE(32768);
 COSTABLE(65536);
 COSTABLE(131072);
 DECLARE_ALIGNED(32, FFTComplex, TX_NAME(ff_cos_53))[4];
 
 static FFTSample * const cos_tabs[18] = {
     NULL,
     NULL,
     NULL,
     NULL,
     TX_NAME(ff_cos_16),
     TX_NAME(ff_cos_32),
     TX_NAME(ff_cos_64),
     TX_NAME(ff_cos_128),
     TX_NAME(ff_cos_256),
     TX_NAME(ff_cos_512),
     TX_NAME(ff_cos_1024),
     TX_NAME(ff_cos_2048),
     TX_NAME(ff_cos_4096),
     TX_NAME(ff_cos_8192),
     TX_NAME(ff_cos_16384),
     TX_NAME(ff_cos_32768),
     TX_NAME(ff_cos_65536),
     TX_NAME(ff_cos_131072),
 };
 
 static av_always_inline void init_cos_tabs_idx(int index)
 {
     int m = 1 << index;
     double freq = 2*M_PI/m;
     FFTSample *tab = cos_tabs[index];
     for(int i = 0; i <= m/4; i++)
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         tab[i] = RESCALE(cos(i*freq));
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     for(int i = 1; i < m/4; i++)
         tab[m/2 - i] = tab[i];
 }
 
 #define INIT_FF_COS_TABS_FUNC(index, size)                                     \
 static av_cold void init_cos_tabs_ ## size (void)                              \
 {                                                                              \
     init_cos_tabs_idx(index);                                                  \
 }
 
 INIT_FF_COS_TABS_FUNC(4, 16)
 INIT_FF_COS_TABS_FUNC(5, 32)
 INIT_FF_COS_TABS_FUNC(6, 64)
 INIT_FF_COS_TABS_FUNC(7, 128)
 INIT_FF_COS_TABS_FUNC(8, 256)
 INIT_FF_COS_TABS_FUNC(9, 512)
 INIT_FF_COS_TABS_FUNC(10, 1024)
 INIT_FF_COS_TABS_FUNC(11, 2048)
 INIT_FF_COS_TABS_FUNC(12, 4096)
 INIT_FF_COS_TABS_FUNC(13, 8192)
 INIT_FF_COS_TABS_FUNC(14, 16384)
 INIT_FF_COS_TABS_FUNC(15, 32768)
 INIT_FF_COS_TABS_FUNC(16, 65536)
 INIT_FF_COS_TABS_FUNC(17, 131072)
 
 static av_cold void ff_init_53_tabs(void)
 {
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     TX_NAME(ff_cos_53)[0] = (FFTComplex){ RESCALE(cos(2 * M_PI / 12)), RESCALE(cos(2 * M_PI / 12)) };
     TX_NAME(ff_cos_53)[1] = (FFTComplex){ RESCALE(cos(2 * M_PI /  6)), RESCALE(cos(2 * M_PI /  6)) };
     TX_NAME(ff_cos_53)[2] = (FFTComplex){ RESCALE(cos(2 * M_PI /  5)), RESCALE(sin(2 * M_PI /  5)) };
     TX_NAME(ff_cos_53)[3] = (FFTComplex){ RESCALE(cos(2 * M_PI / 10)), RESCALE(sin(2 * M_PI / 10)) };
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 }
 
 static CosTabsInitOnce cos_tabs_init_once[] = {
     { ff_init_53_tabs, AV_ONCE_INIT },
     { NULL },
     { NULL },
     { NULL },
     { init_cos_tabs_16, AV_ONCE_INIT },
     { init_cos_tabs_32, AV_ONCE_INIT },
     { init_cos_tabs_64, AV_ONCE_INIT },
     { init_cos_tabs_128, AV_ONCE_INIT },
     { init_cos_tabs_256, AV_ONCE_INIT },
     { init_cos_tabs_512, AV_ONCE_INIT },
     { init_cos_tabs_1024, AV_ONCE_INIT },
     { init_cos_tabs_2048, AV_ONCE_INIT },
     { init_cos_tabs_4096, AV_ONCE_INIT },
     { init_cos_tabs_8192, AV_ONCE_INIT },
     { init_cos_tabs_16384, AV_ONCE_INIT },
     { init_cos_tabs_32768, AV_ONCE_INIT },
     { init_cos_tabs_65536, AV_ONCE_INIT },
     { init_cos_tabs_131072, AV_ONCE_INIT },
 };
 
 static av_cold void init_cos_tabs(int index)
 {
     ff_thread_once(&cos_tabs_init_once[index].control,
                     cos_tabs_init_once[index].func);
 }
 
 static av_always_inline void fft3(FFTComplex *out, FFTComplex *in,
                                   ptrdiff_t stride)
 {
     FFTComplex tmp[2];
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 #ifdef TX_INT32
     int64_t mtmp[4];
 #endif
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     BF(tmp[0].re, tmp[1].im, in[1].im, in[2].im);
     BF(tmp[0].im, tmp[1].re, in[1].re, in[2].re);
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     out[0*stride].re = in[0].re + tmp[1].re;
     out[0*stride].im = in[0].im + tmp[1].im;
 
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 #ifdef TX_INT32
     mtmp[0] = (int64_t)TX_NAME(ff_cos_53)[0].re * tmp[0].re;
     mtmp[1] = (int64_t)TX_NAME(ff_cos_53)[0].im * tmp[0].im;
     mtmp[2] = (int64_t)TX_NAME(ff_cos_53)[1].re * tmp[1].re;
     mtmp[3] = (int64_t)TX_NAME(ff_cos_53)[1].re * tmp[1].im;
     out[1*stride].re = in[0].re - (mtmp[2] + mtmp[0] + 0x40000000 >> 31);
     out[1*stride].im = in[0].im - (mtmp[3] - mtmp[1] + 0x40000000 >> 31);
     out[2*stride].re = in[0].re - (mtmp[2] - mtmp[0] + 0x40000000 >> 31);
     out[2*stride].im = in[0].im - (mtmp[3] + mtmp[1] + 0x40000000 >> 31);
 #else
     tmp[0].re = TX_NAME(ff_cos_53)[0].re * tmp[0].re;
     tmp[0].im = TX_NAME(ff_cos_53)[0].im * tmp[0].im;
     tmp[1].re = TX_NAME(ff_cos_53)[1].re * tmp[1].re;
     tmp[1].im = TX_NAME(ff_cos_53)[1].re * tmp[1].im;
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     out[1*stride].re = in[0].re - tmp[1].re + tmp[0].re;
     out[1*stride].im = in[0].im - tmp[1].im - tmp[0].im;
     out[2*stride].re = in[0].re - tmp[1].re - tmp[0].re;
     out[2*stride].im = in[0].im - tmp[1].im + tmp[0].im;
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 #endif
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 }
 
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 #define DECL_FFT5(NAME, D0, D1, D2, D3, D4)                                                       \
 static av_always_inline void NAME(FFTComplex *out, FFTComplex *in,                                \
                                   ptrdiff_t stride)                                               \
 {                                                                                                 \
     FFTComplex z0[4], t[6];                                                                       \
                                                                                                   \
     BF(t[1].im, t[0].re, in[1].re, in[4].re);                                                     \
     BF(t[1].re, t[0].im, in[1].im, in[4].im);                                                     \
     BF(t[3].im, t[2].re, in[2].re, in[3].re);                                                     \
     BF(t[3].re, t[2].im, in[2].im, in[3].im);                                                     \
                                                                                                   \
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     out[D0*stride].re = in[0].re + t[0].re + t[2].re;                                             \
     out[D0*stride].im = in[0].im + t[0].im + t[2].im;                                             \
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                                                                                                   \
     SMUL(t[4].re, t[0].re, TX_NAME(ff_cos_53)[2].re, TX_NAME(ff_cos_53)[3].re, t[2].re, t[0].re); \
     SMUL(t[4].im, t[0].im, TX_NAME(ff_cos_53)[2].re, TX_NAME(ff_cos_53)[3].re, t[2].im, t[0].im); \
     CMUL(t[5].re, t[1].re, TX_NAME(ff_cos_53)[2].im, TX_NAME(ff_cos_53)[3].im, t[3].re, t[1].re); \
     CMUL(t[5].im, t[1].im, TX_NAME(ff_cos_53)[2].im, TX_NAME(ff_cos_53)[3].im, t[3].im, t[1].im); \
                                                                                                   \
     BF(z0[0].re, z0[3].re, t[0].re, t[1].re);                                                     \
     BF(z0[0].im, z0[3].im, t[0].im, t[1].im);                                                     \
     BF(z0[2].re, z0[1].re, t[4].re, t[5].re);                                                     \
     BF(z0[2].im, z0[1].im, t[4].im, t[5].im);                                                     \
                                                                                                   \
     out[D1*stride].re = in[0].re + z0[3].re;                                                      \
     out[D1*stride].im = in[0].im + z0[0].im;                                                      \
     out[D2*stride].re = in[0].re + z0[2].re;                                                      \
     out[D2*stride].im = in[0].im + z0[1].im;                                                      \
     out[D3*stride].re = in[0].re + z0[1].re;                                                      \
     out[D3*stride].im = in[0].im + z0[2].im;                                                      \
     out[D4*stride].re = in[0].re + z0[0].re;                                                      \
     out[D4*stride].im = in[0].im + z0[3].im;                                                      \
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 }
 
 DECL_FFT5(fft5,     0,  1,  2,  3,  4)
 DECL_FFT5(fft5_m1,  0,  6, 12,  3,  9)
 DECL_FFT5(fft5_m2, 10,  1,  7, 13,  4)
 DECL_FFT5(fft5_m3,  5, 11,  2,  8, 14)
 
 static av_always_inline void fft15(FFTComplex *out, FFTComplex *in,
                                    ptrdiff_t stride)
 {
     FFTComplex tmp[15];
 
     for (int i = 0; i < 5; i++)
         fft3(tmp + i, in + i*3, 5);
 
     fft5_m1(out, tmp +  0, stride);
     fft5_m2(out, tmp +  5, stride);
     fft5_m3(out, tmp + 10, stride);
 }
 
 #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) {\
     CMUL(t1, t2, a2.re, a2.im, wre, -wim);\
     CMUL(t5, t6, a3.re, a3.im, wre,  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,TX_NAME(ff_cos_##n),n4/2);\
 }
 
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 static void fft2(FFTComplex *z)
 {
     FFTComplex tmp;
     BF(tmp.re, z[0].re, z[0].re, z[1].re);
     BF(tmp.im, z[0].im, z[0].im, z[1].im);
     z[1] = tmp;
 }
 
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 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;
 
     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(t5, z[7].re, z[6].re, -z[7].re);
     BF(t6, z[7].im, z[6].im, -z[7].im);
 
     BUTTERFLIES(z[0],z[2],z[4],z[6]);
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     TRANSFORM(z[1],z[3],z[5],z[7],RESCALE(M_SQRT1_2),RESCALE(M_SQRT1_2));
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 }
 
 static void fft16(FFTComplex *z)
 {
     FFTSample t1, t2, t3, t4, t5, t6;
     FFTSample cos_16_1 = TX_NAME(ff_cos_16)[1];
     FFTSample cos_16_3 = TX_NAME(ff_cos_16)[3];
 
     fft8(z);
     fft4(z+8);
     fft4(z+12);
 
     TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
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     TRANSFORM(z[2],z[6],z[10],z[14],RESCALE(M_SQRT1_2),RESCALE(M_SQRT1_2));
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     TRANSFORM(z[1],z[5],z[9],z[13],cos_16_1,cos_16_3);
     TRANSFORM(z[3],z[7],z[11],z[15],cos_16_3,cos_16_1);
 }
 
 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)
 #define pass pass_big
 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)
 DECL_FFT(131072,65536,32768)
 
 static void (* const fft_dispatch[])(FFTComplex*) = {
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     NULL, fft2, fft4, fft8, fft16, fft32, fft64, fft128, fft256, fft512,
     fft1024, fft2048, fft4096, fft8192, fft16384, fft32768, fft65536, fft131072
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 };
 
 #define DECL_COMP_FFT(N)                                                       \
 static void compound_fft_##N##xM(AVTXContext *s, void *_out,                   \
                                  void *_in, ptrdiff_t stride)                  \
 {                                                                              \
     const int m = s->m, *in_map = s->pfatab, *out_map = in_map + N*m;          \
     FFTComplex *in = _in;                                                      \
     FFTComplex *out = _out;                                                    \
     FFTComplex fft##N##in[N];                                                  \
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     void (*fftp)(FFTComplex *z) = fft_dispatch[av_log2(m)];                    \
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                                                                                \
     for (int i = 0; i < m; i++) {                                              \
         for (int j = 0; j < N; j++)                                            \
             fft##N##in[j] = in[in_map[i*N + j]];                               \
         fft##N(s->tmp + s->revtab[i], fft##N##in, m);                          \
     }                                                                          \
                                                                                \
     for (int i = 0; i < N; i++)                                                \
         fftp(s->tmp + m*i);                                                    \
                                                                                \
     for (int i = 0; i < N*m; i++)                                              \
         out[i] = s->tmp[out_map[i]];                                           \
 }
 
 DECL_COMP_FFT(3)
 DECL_COMP_FFT(5)
 DECL_COMP_FFT(15)
 
 static void monolithic_fft(AVTXContext *s, void *_out, void *_in,
                            ptrdiff_t stride)
 {
     FFTComplex *in = _in;
     FFTComplex *out = _out;
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     int m = s->m, mb = av_log2(m);
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     for (int i = 0; i < m; i++)
         out[s->revtab[i]] = in[i];
     fft_dispatch[mb](out);
 }
 
 #define DECL_COMP_IMDCT(N)                                                     \
 static void compound_imdct_##N##xM(AVTXContext *s, void *_dst, void *_src,     \
                                    ptrdiff_t stride)                           \
 {                                                                              \
     FFTComplex fft##N##in[N];                                                  \
     FFTComplex *z = _dst, *exp = s->exptab;                                    \
     const int m = s->m, len8 = N*m >> 1;                                       \
     const int *in_map = s->pfatab, *out_map = in_map + N*m;                    \
     const FFTSample *src = _src, *in1, *in2;                                   \
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     void (*fftp)(FFTComplex *) = fft_dispatch[av_log2(m)];                     \
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                                                                                \
     stride /= sizeof(*src); /* To convert it from bytes */                     \
     in1 = src;                                                                 \
     in2 = src + ((N*m*2) - 1) * stride;                                        \
                                                                                \
     for (int i = 0; i < m; i++) {                                              \
         for (int j = 0; j < N; j++) {                                          \
             const int k = in_map[i*N + j];                                     \
             FFTComplex tmp = { in2[-k*stride], in1[k*stride] };                \
             CMUL3(fft##N##in[j], tmp, exp[k >> 1]);                            \
         }                                                                      \
         fft##N(s->tmp + s->revtab[i], fft##N##in, m);                          \
     }                                                                          \
                                                                                \
     for (int i = 0; i < N; i++)                                                \
         fftp(s->tmp + m*i);                                                    \
                                                                                \
     for (int i = 0; i < len8; i++) {                                           \
         const int i0 = len8 + i, i1 = len8 - i - 1;                            \
         const int s0 = out_map[i0], s1 = out_map[i1];                          \
         FFTComplex src1 = { s->tmp[s1].im, s->tmp[s1].re };                    \
         FFTComplex src0 = { s->tmp[s0].im, s->tmp[s0].re };                    \
                                                                                \
         CMUL(z[i1].re, z[i0].im, src1.re, src1.im, exp[i1].im, exp[i1].re);    \
         CMUL(z[i0].re, z[i1].im, src0.re, src0.im, exp[i0].im, exp[i0].re);    \
     }                                                                          \
 }
 
 DECL_COMP_IMDCT(3)
 DECL_COMP_IMDCT(5)
 DECL_COMP_IMDCT(15)
 
 #define DECL_COMP_MDCT(N)                                                      \
 static void compound_mdct_##N##xM(AVTXContext *s, void *_dst, void *_src,      \
                                   ptrdiff_t stride)                            \
 {                                                                              \
     FFTSample *src = _src, *dst = _dst;                                        \
     FFTComplex *exp = s->exptab, tmp, fft##N##in[N];                           \
     const int m = s->m, len4 = N*m, len3 = len4 * 3, len8 = len4 >> 1;         \
     const int *in_map = s->pfatab, *out_map = in_map + N*m;                    \
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     void (*fftp)(FFTComplex *) = fft_dispatch[av_log2(m)];                     \
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                                                                                \
     stride /= sizeof(*dst);                                                    \
                                                                                \
     for (int i = 0; i < m; i++) { /* Folding and pre-reindexing */             \
         for (int j = 0; j < N; j++) {                                          \
             const int k = in_map[i*N + j];                                     \
             if (k < len4) {                                                    \
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                 tmp.re = FOLD(-src[ len4 + k],  src[1*len4 - 1 - k]);          \
                 tmp.im = FOLD(-src[ len3 + k], -src[1*len3 - 1 - k]);          \
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             } else {                                                           \
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                 tmp.re = FOLD(-src[ len4 + k], -src[5*len4 - 1 - k]);          \
                 tmp.im = FOLD( src[-len4 + k], -src[1*len3 - 1 - k]);          \
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             }                                                                  \
             CMUL(fft##N##in[j].im, fft##N##in[j].re, tmp.re, tmp.im,           \
                  exp[k >> 1].re, exp[k >> 1].im);                              \
         }                                                                      \
         fft##N(s->tmp + s->revtab[i], fft##N##in, m);                          \
     }                                                                          \
                                                                                \
     for (int i = 0; i < N; i++)                                                \
         fftp(s->tmp + m*i);                                                    \
                                                                                \
     for (int i = 0; i < len8; i++) {                                           \
         const int i0 = len8 + i, i1 = len8 - i - 1;                            \
         const int s0 = out_map[i0], s1 = out_map[i1];                          \
         FFTComplex src1 = { s->tmp[s1].re, s->tmp[s1].im };                    \
         FFTComplex src0 = { s->tmp[s0].re, s->tmp[s0].im };                    \
                                                                                \
         CMUL(dst[2*i1*stride + stride], dst[2*i0*stride], src0.re, src0.im,    \
              exp[i0].im, exp[i0].re);                                          \
         CMUL(dst[2*i0*stride + stride], dst[2*i1*stride], src1.re, src1.im,    \
              exp[i1].im, exp[i1].re);                                          \
     }                                                                          \
 }
 
 DECL_COMP_MDCT(3)
 DECL_COMP_MDCT(5)
 DECL_COMP_MDCT(15)
 
 static void monolithic_imdct(AVTXContext *s, void *_dst, void *_src,
                              ptrdiff_t stride)
 {
     FFTComplex *z = _dst, *exp = s->exptab;
     const int m = s->m, len8 = m >> 1;
     const FFTSample *src = _src, *in1, *in2;
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     void (*fftp)(FFTComplex *) = fft_dispatch[av_log2(m)];
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     stride /= sizeof(*src);
     in1 = src;
     in2 = src + ((m*2) - 1) * stride;
 
     for (int i = 0; i < m; i++) {
         FFTComplex tmp = { in2[-2*i*stride], in1[2*i*stride] };
         CMUL3(z[s->revtab[i]], tmp, exp[i]);
     }
 
     fftp(z);
 
     for (int i = 0; i < len8; i++) {
         const int i0 = len8 + i, i1 = len8 - i - 1;
         FFTComplex src1 = { z[i1].im, z[i1].re };
         FFTComplex src0 = { z[i0].im, z[i0].re };
 
         CMUL(z[i1].re, z[i0].im, src1.re, src1.im, exp[i1].im, exp[i1].re);
         CMUL(z[i0].re, z[i1].im, src0.re, src0.im, exp[i0].im, exp[i0].re);
     }
 }
 
 static void monolithic_mdct(AVTXContext *s, void *_dst, void *_src,
                             ptrdiff_t stride)
 {
     FFTSample *src = _src, *dst = _dst;
     FFTComplex *exp = s->exptab, tmp, *z = _dst;
     const int m = s->m, len4 = m, len3 = len4 * 3, len8 = len4 >> 1;
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     void (*fftp)(FFTComplex *) = fft_dispatch[av_log2(m)];
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     stride /= sizeof(*dst);
 
     for (int i = 0; i < m; i++) { /* Folding and pre-reindexing */
         const int k = 2*i;
         if (k < len4) {
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             tmp.re = FOLD(-src[ len4 + k],  src[1*len4 - 1 - k]);
             tmp.im = FOLD(-src[ len3 + k], -src[1*len3 - 1 - k]);
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         } else {
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             tmp.re = FOLD(-src[ len4 + k], -src[5*len4 - 1 - k]);
             tmp.im = FOLD( src[-len4 + k], -src[1*len3 - 1 - k]);
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         }
         CMUL(z[s->revtab[i]].im, z[s->revtab[i]].re, tmp.re, tmp.im,
              exp[i].re, exp[i].im);
     }
 
     fftp(z);
 
     for (int i = 0; i < len8; i++) {
         const int i0 = len8 + i, i1 = len8 - i - 1;
         FFTComplex src1 = { z[i1].re, z[i1].im };
         FFTComplex src0 = { z[i0].re, z[i0].im };
 
         CMUL(dst[2*i1*stride + stride], dst[2*i0*stride], src0.re, src0.im,
              exp[i0].im, exp[i0].re);
         CMUL(dst[2*i0*stride + stride], dst[2*i1*stride], src1.re, src1.im,
              exp[i1].im, exp[i1].re);
     }
 }
 
 static int gen_mdct_exptab(AVTXContext *s, int len4, double scale)
 {
     const double theta = (scale < 0 ? len4 : 0) + 1.0/8.0;
 
     if (!(s->exptab = av_malloc_array(len4, sizeof(*s->exptab))))
         return AVERROR(ENOMEM);
 
     scale = sqrt(fabs(scale));
     for (int i = 0; i < len4; i++) {
         const double alpha = M_PI_2 * (i + theta) / len4;
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         s->exptab[i].re = RESCALE(cos(alpha) * scale);
         s->exptab[i].im = RESCALE(sin(alpha) * scale);
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     }
 
     return 0;
 }
 
 int TX_NAME(ff_tx_init_mdct_fft)(AVTXContext *s, av_tx_fn *tx,
                                  enum AVTXType type, int inv, int len,
                                  const void *scale, uint64_t flags)
 {
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     const int is_mdct = ff_tx_type_is_mdct(type);
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     int err, n = 1, m = 1, max_ptwo = 1 << (FF_ARRAY_ELEMS(fft_dispatch) - 1);
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     if (is_mdct)
         len >>= 1;
 
 #define CHECK_FACTOR(DST, FACTOR, SRC)                                         \
     if (DST == 1 && !(SRC % FACTOR)) {                                         \
         DST = FACTOR;                                                          \
         SRC /= FACTOR;                                                         \
     }
     CHECK_FACTOR(n, 15, len)
     CHECK_FACTOR(n,  5, len)
     CHECK_FACTOR(n,  3, len)
a38c6f47
 #undef CHECK_FACTOR
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     /* len must be a power of two now */
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     if (!(len & (len - 1)) && len >= 2 && len <= max_ptwo) {
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         m = len;
         len = 1;
     }
 
     s->n = n;
     s->m = m;
     s->inv = inv;
     s->type = type;
 
     /* Filter out direct 3, 5 and 15 transforms, too niche */
     if (len > 1 || m == 1) {
         av_log(NULL, AV_LOG_ERROR, "Unsupported transform size: n = %i, "
                "m = %i, residual = %i!\n", n, m, len);
         return AVERROR(EINVAL);
     } else if (n > 1 && m > 1) { /* 2D transform case */
         if ((err = ff_tx_gen_compound_mapping(s)))
             return err;
         if (!(s->tmp = av_malloc(n*m*sizeof(*s->tmp))))
             return AVERROR(ENOMEM);
         *tx = n == 3 ? compound_fft_3xM :
               n == 5 ? compound_fft_5xM :
                        compound_fft_15xM;
         if (is_mdct)
             *tx = n == 3 ? inv ? compound_imdct_3xM  : compound_mdct_3xM :
                   n == 5 ? inv ? compound_imdct_5xM  : compound_mdct_5xM :
                            inv ? compound_imdct_15xM : compound_mdct_15xM;
     } else { /* Direct transform case */
         *tx = monolithic_fft;
         if (is_mdct)
             *tx = inv ? monolithic_imdct : monolithic_mdct;
     }
 
     if (n != 1)
         init_cos_tabs(0);
     if (m != 1) {
         ff_tx_gen_ptwo_revtab(s);
         for (int i = 4; i <= av_log2(m); i++)
             init_cos_tabs(i);
     }
 
     if (is_mdct)
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         return gen_mdct_exptab(s, n*m, *((SCALE_TYPE *)scale));
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     return 0;
 }