| /* |
| * (I)RDFT transforms |
| * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com> |
| * |
| * 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 <stdlib.h> |
| #include <math.h> |
| #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); |
| } |