/*
  * Copyright (c) 2011  Justin Ruggles
  *

  * 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 "libavutil/common.h"

 #include "libavutil/intreadwrite.h"

 #include "libavutil/mathematics.h"
 #include "adx.h"
 
 void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
 {
     double a, b, c;
 
     a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
     b = M_SQRT2 - 1.0;
     c = (a - sqrt((a + b) * (a - b))) / b;
 
     coeff[0] = lrintf(c * 2.0  * (1 << bits));
     coeff[1] = lrintf(-(c * c) * (1 << bits));
 }

 int ff_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
                          int bufsize, int *header_size, int *coeff)

 {
     int offset, cutoff;
 
     if (bufsize < 24)
         return AVERROR_INVALIDDATA;
 
     if (AV_RB16(buf) != 0x8000)
         return AVERROR_INVALIDDATA;
     offset = AV_RB16(buf + 2) + 4;
 
     /* if copyright string is within the provided data, validate it */

     if (bufsize >= offset && offset >= 6 && memcmp(buf + offset - 6, "(c)CRI", 6))

         return AVERROR_INVALIDDATA;
 
     /* check for encoding=3 block_size=18, sample_size=4 */
     if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {

         avpriv_request_sample(avctx, "Support for this ADX format");

         return AVERROR_PATCHWELCOME;
     }
 
     /* channels */
     avctx->channels = buf[7];

     if (avctx->channels <= 0 || avctx->channels > 2)

         return AVERROR_INVALIDDATA;
 
     /* sample rate */
     avctx->sample_rate = AV_RB32(buf + 8);
     if (avctx->sample_rate < 1 ||
         avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
         return AVERROR_INVALIDDATA;
 
     /* bit rate */
     avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
 
     /* LPC coefficients */
     if (coeff) {
         cutoff = AV_RB16(buf + 16);
         ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
     }
 
     *header_size = offset;
     return 0;
 }