1/*
2 * Copyright (c) 2011  Justin Ruggles
3 *
4 * This file is part of Libav.
5 *
6 * Libav is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * Libav is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with Libav; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21#include "libavutil/intreadwrite.h"
22#include "libavutil/mathematics.h"
23#include "adx.h"
24
25void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
26{
27    double a, b, c;
28
29    a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
30    b = M_SQRT2 - 1.0;
31    c = (a - sqrt((a + b) * (a - b))) / b;
32
33    coeff[0] = lrintf(c * 2.0  * (1 << bits));
34    coeff[1] = lrintf(-(c * c) * (1 << bits));
35}
36
37int avpriv_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
38                             int bufsize, int *header_size, int *coeff)
39{
40    int offset, cutoff;
41
42    if (bufsize < 24)
43        return AVERROR_INVALIDDATA;
44
45    if (AV_RB16(buf) != 0x8000)
46        return AVERROR_INVALIDDATA;
47    offset = AV_RB16(buf + 2) + 4;
48
49    /* if copyright string is within the provided data, validate it */
50    if (bufsize >= offset && memcmp(buf + offset - 6, "(c)CRI", 6))
51        return AVERROR_INVALIDDATA;
52
53    /* check for encoding=3 block_size=18, sample_size=4 */
54    if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
55        av_log_ask_for_sample(avctx, "unsupported ADX format\n");
56        return AVERROR_PATCHWELCOME;
57    }
58
59    /* channels */
60    avctx->channels = buf[7];
61    if (avctx->channels <= 0 || avctx->channels > 2)
62        return AVERROR_INVALIDDATA;
63
64    /* sample rate */
65    avctx->sample_rate = AV_RB32(buf + 8);
66    if (avctx->sample_rate < 1 ||
67        avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
68        return AVERROR_INVALIDDATA;
69
70    /* bit rate */
71    avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
72
73    /* LPC coefficients */
74    if (coeff) {
75        cutoff = AV_RB16(buf + 16);
76        ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
77    }
78
79    *header_size = offset;
80    return 0;
81}
82