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#include "common.h"
/*****************************************************************************
*
* CRC error protection package
*
*****************************************************************************/
void CRC_calc(frame_params *fr_ps,
unsigned int bit_alloc[2][SBLIMIT],
unsigned int scfsi[2][SBLIMIT],
unsigned int *crc)
{
int i, k;
layer *info = fr_ps->header;
int stereo = fr_ps->stereo;
int sblimit = fr_ps->sblimit;
int jsbound = fr_ps->jsbound;
al_table *alloc = fr_ps->alloc;
*crc = 0xffff; /* changed from '0' 92-08-11 shn */
update_CRC(info->bitrate_index, 4, crc);
update_CRC(info->sampling_frequency, 2, crc);
update_CRC(info->padding, 1, crc);
update_CRC(info->extension, 1, crc);
update_CRC(info->mode, 2, crc);
update_CRC(info->mode_ext, 2, crc);
update_CRC(info->copyright, 1, crc);
update_CRC(info->original, 1, crc);
update_CRC(info->emphasis, 2, crc);
for (i=0;i<sblimit;i++)
for (k=0;k<((i<jsbound)?stereo:1);k++)
update_CRC(bit_alloc[k][i], (*alloc)[i][0].bits, crc);
for (i=0;i<sblimit;i++)
for (k=0;k<stereo;k++)
if (bit_alloc[k][i])
update_CRC(scfsi[k][i], 2, crc);
}
void update_CRC(unsigned int data, unsigned int length, unsigned int *crc)
{
unsigned int masking, carry;
masking = 1 << length;
while((masking >>= 1))
{
carry = *crc & 0x8000;
*crc <<= 1;
if (!carry ^ !(data & masking))
*crc ^= CRC16_POLYNOMIAL;
}
*crc &= 0xffff;
}
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