/* * MDCT/IMDCT transforms * Copyright (c) 2002 Fabrice Bellard * * 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 <string.h> #include "libavutil/common.h" #include "libavutil/mathematics.h" #include "fft.h" #include "fft-internal.h" /** * @file * MDCT/IMDCT transforms. */ #if CONFIG_FFT_FLOAT # define RSCALE(x) (x) #else #if CONFIG_FFT_FIXED_32 # define RSCALE(x) (((x) + 32) >> 6) #else /* CONFIG_FFT_FIXED_32 */ # define RSCALE(x) ((x) >> 1) #endif /* CONFIG_FFT_FIXED_32 */ #endif /** * init MDCT or IMDCT computation. */ av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale) { int n, n4, i; double alpha, theta; int tstep; memset(s, 0, sizeof(*s)); n = 1 << nbits; s->mdct_bits = nbits; s->mdct_size = n; n4 = n >> 2; s->mdct_permutation = FF_MDCT_PERM_NONE; if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0) goto fail; s->tcos = av_malloc(n/2 * sizeof(FFTSample)); if (!s->tcos) goto fail; switch (s->mdct_permutation) { case FF_MDCT_PERM_NONE: s->tsin = s->tcos + n4; tstep = 1; break; case FF_MDCT_PERM_INTERLEAVE: s->tsin = s->tcos + 1; tstep = 2; break; default: goto fail; } theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0); scale = sqrt(fabs(scale)); for(i=0;i<n4;i++) { alpha = 2 * M_PI * (i + theta) / n; s->tcos[i*tstep] = FIX15(-cos(alpha) * scale); s->tsin[i*tstep] = FIX15(-sin(alpha) * scale); } return 0; fail: ff_mdct_end(s); return -1; } /** * Compute the middle half of the inverse MDCT of size N = 2^nbits, * thus excluding the parts that can be derived by symmetry * @param output N/2 samples * @param input N/2 samples */ void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input) { int k, n8, n4, n2, n, j; const uint16_t *revtab = s->revtab; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; const FFTSample *in1, *in2; FFTComplex *z = (FFTComplex *)output; n = 1 << s->mdct_bits; n2 = n >> 1; n4 = n >> 2; n8 = n >> 3; /* pre rotation */ in1 = input; in2 = input + n2 - 1; for(k = 0; k < n4; k++) { j=revtab[k]; CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]); in1 += 2; in2 -= 2; } s->fft_calc(s, z); /* post rotation + reordering */ for(k = 0; k < n8; k++) { FFTSample r0, i0, r1, i1; CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]); CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]); z[n8-k-1].re = r0; z[n8-k-1].im = i0; z[n8+k ].re = r1; z[n8+k ].im = i1; } } /** * Compute inverse MDCT of size N = 2^nbits * @param output N samples * @param input N/2 samples */ void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input) { int k; int n = 1 << s->mdct_bits; int n2 = n >> 1; int n4 = n >> 2; ff_imdct_half_c(s, output+n4, input); for(k = 0; k < n4; k++) { output[k] = -output[n2-k-1]; output[n-k-1] = output[n2+k]; } } /** * Compute MDCT of size N = 2^nbits * @param input N samples * @param out N/2 samples */ void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input) { int i, j, n, n8, n4, n2, n3; FFTDouble re, im; const uint16_t *revtab = s->revtab; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; FFTComplex *x = (FFTComplex *)out; n = 1 << s->mdct_bits; n2 = n >> 1; n4 = n >> 2; n8 = n >> 3; n3 = 3 * n4; /* pre rotation */ for(i=0;i<n8;i++) { re = RSCALE(-input[2*i+n3] - input[n3-1-2*i]); im = RSCALE(-input[n4+2*i] + input[n4-1-2*i]); j = revtab[i]; CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]); re = RSCALE( input[2*i] - input[n2-1-2*i]); im = RSCALE(-input[n2+2*i] - input[ n-1-2*i]); j = revtab[n8 + i]; CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]); } s->fft_calc(s, x); /* post rotation */ for(i=0;i<n8;i++) { FFTSample r0, i0, r1, i1; CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]); CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]); x[n8-i-1].re = r0; x[n8-i-1].im = i0; x[n8+i ].re = r1; x[n8+i ].im = i1; } } av_cold void ff_mdct_end(FFTContext *s) { av_freep(&s->tcos); ff_fft_end(s); }