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 /* * (I)RDFT transforms * Copyright (c) 2009 Alex Converse * * 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 */ #include #include #include "libavutil/mathematics.h" #include "rdft.h" /** * @file * (Inverse) Real Discrete Fourier Transforms. */ /** Map one real FFT into two parallel real even and odd FFTs. Then interleave * the two real FFTs into one complex FFT. Unmangle the results. * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM */ static void rdft_calc_c(RDFTContext *s, FFTSample *data) { int i, i1, i2; FFTComplex ev, od, odsum; const int n = 1 << s->nbits; const float k1 = 0.5; const float k2 = 0.5 - s->inverse; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; if (!s->inverse) { s->fft.fft_permute(&s->fft, (FFTComplex*)data); s->fft.fft_calc(&s->fft, (FFTComplex*)data); } /* i=0 is a special case because of packing, the DC term is real, so we are going to throw the N/2 term (also real) in with it. */ ev.re = data[0]; data[0] = ev.re+data[1]; data[1] = ev.re-data[1]; #define RDFT_UNMANGLE(sign0, sign1) \ for (i = 1; i < (n>>2); i++) { \ i1 = 2*i; \ i2 = n-i1; \ /* Separate even and odd FFTs */ \ ev.re = k1*(data[i1 ]+data[i2 ]); \ od.im = k2*(data[i2 ]-data[i1 ]); \ ev.im = k1*(data[i1+1]-data[i2+1]); \ od.re = k2*(data[i1+1]+data[i2+1]); \ /* Apply twiddle factors to the odd FFT and add to the even FFT */ \ odsum.re = od.re*tcos[i] sign0 od.im*tsin[i]; \ odsum.im = od.im*tcos[i] sign1 od.re*tsin[i]; \ data[i1 ] = ev.re + odsum.re; \ data[i1+1] = ev.im + odsum.im; \ data[i2 ] = ev.re - odsum.re; \ data[i2+1] = odsum.im - ev.im; \ } if (s->negative_sin) { RDFT_UNMANGLE(+,-) } else { RDFT_UNMANGLE(-,+) } data[2*i+1]=s->sign_convention*data[2*i+1]; if (s->inverse) { data[0] *= k1; data[1] *= k1; s->fft.fft_permute(&s->fft, (FFTComplex*)data); s->fft.fft_calc(&s->fft, (FFTComplex*)data); } } av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans) { int n = 1 << nbits; int ret; s->nbits = nbits; s->inverse = trans == IDFT_C2R || trans == DFT_C2R; s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; s->negative_sin = trans == DFT_C2R || trans == DFT_R2C; if (nbits < 4 || nbits > 16) return AVERROR(EINVAL); if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0) return ret; ff_init_ff_cos_tabs(nbits); s->tcos = ff_cos_tabs[nbits]; s->tsin = ff_cos_tabs[nbits] + (n >> 2); s->rdft_calc = rdft_calc_c; if (ARCH_ARM) ff_rdft_init_arm(s); return 0; } av_cold void ff_rdft_end(RDFTContext *s) { ff_fft_end(&s->fft); }