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/*
* (I)DCT Transforms
* Copyright (c) 2009 Peter Ross <pross@xvid.org>
* Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>
* Copyright (c) 2010 Vitor Sessak
*
* 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 St, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file libavcodec/dct.c
* (Inverse) Discrete Cosine Transforms. These are also known as the
* type II and type III DCTs respectively.
*/
#include <math.h>
#include "dsputil.h"
av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
{
int n = 1 << nbits;
int i;
s->nbits = nbits;
s->inverse = inverse;
ff_init_ff_cos_tabs(nbits+2);
s->costab = ff_cos_tabs[nbits+2];
s->csc2 = av_malloc(n/2 * sizeof(FFTSample));
if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {
av_free(s->csc2);
return -1;
}
for (i = 0; i < n/2; i++)
s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));
return 0;
}
/* sin((M_PI * x / (2*n)) */
#define SIN(s,n,x) (s->costab[(n) - (x)])
/* cos((M_PI * x / (2*n)) */
#define COS(s,n,x) (s->costab[x])
static void ff_dct_calc_c(DCTContext *ctx, FFTSample *data)
{
int n = 1 << ctx->nbits;
int i;
if (ctx->inverse) {
float next = data[n - 1];
float inv_n = 1.0f / n;
for (i = n - 2; i >= 2; i -= 2) {
float val1 = data[i ];
float val2 = data[i - 1] - data[i + 1];
float c = COS(ctx, n, i);
float s = SIN(ctx, n, i);
data[i ] = c * val1 + s * val2;
data[i + 1] = s * val1 - c * val2;
}
data[1] = 2 * next;
ff_rdft_calc(&ctx->rdft, data);
for (i = 0; i < n / 2; i++) {
float tmp1 = data[i ] * inv_n;
float tmp2 = data[n - i - 1] * inv_n;
float csc = ctx->csc2[i] * (tmp1 - tmp2);
tmp1 += tmp2;
data[i ] = tmp1 + csc;
data[n - i - 1] = tmp1 - csc;
}
} else {
float next;
for (i=0; i < n/2; i++) {
float tmp1 = data[i ];
float tmp2 = data[n - i - 1];
float s = SIN(ctx, n, 2*i + 1);
s *= tmp1 - tmp2;
tmp1 = (tmp1 + tmp2) * 0.5f;
data[i ] = tmp1 + s;
data[n-i-1] = tmp1 - s;
}
ff_rdft_calc(&ctx->rdft, data);
next = data[1] * 0.5;
data[1] *= -1;
for (i = n - 2; i >= 0; i -= 2) {
float inr = data[i ];
float ini = data[i + 1];
float c = COS(ctx, n, i);
float s = SIN(ctx, n, i);
data[i ] = c * inr + s * ini;
data[i+1] = next;
next += s * inr - c * ini;
}
}
}
void ff_dct_calc(DCTContext *s, FFTSample *data)
{
ff_dct_calc_c(s, data);
}
av_cold void ff_dct_end(DCTContext *s)
{
ff_rdft_end(&s->rdft);
av_free(s->csc2);
}
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