common.c

Motion JPEG编解码器源代码

      bs->buf_bit_idx += (tmp - 8);
   }
   bs->buf[bs->buf_byte_idx] &= clearmask[bs->buf_bit_idx];
}

int mask[8]={0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80};

/*read 1 bit from the bit stream */
unsigned int get1bit(bs)
Bit_stream_struc *bs;   /* bit stream structure */
{
   unsigned int bit;
   register int i;

   bs->totbit++;

   if (!bs->buf_bit_idx) {
        bs->buf_bit_idx = 8;
        bs->buf_byte_idx--;
        if ((bs->buf_byte_idx < MINIMUM) || (bs->buf_byte_idx < bs->eob)) {
             if (bs->eob)
                bs->eobs = TRUE;
             else {
                for (i=bs->buf_byte_idx; i>=0;i--)
                  bs->buf[bs->buf_size-1-bs->buf_byte_idx+i] = bs->buf[i];
                refill_buffer(bs);
                bs->buf_byte_idx = bs->buf_size-1;
             }
        }
   }
   bit = bs->buf[bs->buf_byte_idx]&mask[bs->buf_bit_idx-1];
   bit = bit >> (bs->buf_bit_idx-1);
   bs->buf_bit_idx--;
   return(bit);
}

/*write 1 bit from the bit stream */
void put1bit(bs, bit)
Bit_stream_struc *bs;   /* bit stream structure */
int bit;                /* bit to write into the buffer */
{
   bs->totbit++;

   bs->buf[bs->buf_byte_idx] |= (bit&0x1) << (bs->buf_bit_idx-1);
   bs->buf_bit_idx--;
   if (!bs->buf_bit_idx) {
       bs->buf_bit_idx = 8;
       bs->buf_byte_idx--;
       if (bs->buf_byte_idx < 0)
          empty_buffer(bs, MINIMUM);
       bs->buf[bs->buf_byte_idx] = 0;
   }
}

/*look ahead for the next N bits from the bit stream */
unsigned long look_ahead(bs, N)
Bit_stream_struc *bs;   /* bit stream structure */
int N;                  /* number of bits to read from the bit stream */
{
 unsigned long val=0;
 register int j = N;
 register int k, tmp;
 register int bit_idx = bs->buf_bit_idx;
 register int byte_idx = bs->buf_byte_idx;

 if (N > MAX_LENGTH)
    printf("Cannot read or write more than %d bits at a time.\n", MAX_LENGTH);

 while (j > 0) {
    if (!bit_idx) {
        bit_idx = 8;
        byte_idx--;
    }
    k = MIN (j, bit_idx);
    tmp = bs->buf[byte_idx]&putmask[bit_idx];
    tmp = tmp >> (bit_idx-k);
    val |= tmp << (j-k);
    bit_idx -= k;
    j -= k;
 }
 return(val);
}

/*read N bit from the bit stream */
unsigned long getbits(bs, N)
Bit_stream_struc *bs;   /* bit stream structure */
int N;                  /* number of bits to read from the bit stream */
{
 unsigned long val=0;
 register int i;
 register int j = N;
 register int k, tmp;

 if (N > MAX_LENGTH)
    printf("Cannot read or write more than %d bits at a time.\n", MAX_LENGTH);

 bs->totbit += N;
 while (j > 0) {
   if (!bs->buf_bit_idx) {
        bs->buf_bit_idx = 8;
        bs->buf_byte_idx--;
        if ((bs->buf_byte_idx < MINIMUM) || (bs->buf_byte_idx < bs->eob)) {
             if (bs->eob)
                bs->eobs = TRUE;
             else {
                for (i=bs->buf_byte_idx; i>=0;i--)
                   bs->buf[bs->buf_size-1-bs->buf_byte_idx+i] = bs->buf[i];
                refill_buffer(bs);
                bs->buf_byte_idx = bs->buf_size-1;
             }
        }
   }
   k = MIN (j, bs->buf_bit_idx);
   tmp = bs->buf[bs->buf_byte_idx]&putmask[bs->buf_bit_idx];
   tmp = tmp >> (bs->buf_bit_idx-k);
   val |= tmp << (j-k);
   bs->buf_bit_idx -= k;
   j -= k;
 }
 return(val);
}

/*write N bits into the bit stream */
void putbits(bs, val, N)
Bit_stream_struc *bs;   /* bit stream structure */
unsigned int val;       /* val to write into the buffer */
int N;                  /* number of bits of val */
{
 register int j = N;
 register int k, tmp;

 if (N > MAX_LENGTH)
    printf("Cannot read or write more than %d bits at a time.\n", MAX_LENGTH);

 bs->totbit += N;
 while (j > 0) {
   k = MIN(j, bs->buf_bit_idx);
   tmp = val >> (j-k);
   bs->buf[bs->buf_byte_idx] |= (tmp&putmask[k]) << (bs->buf_bit_idx-k);
   bs->buf_bit_idx -= k;
   if (!bs->buf_bit_idx) {
       bs->buf_bit_idx = 8;
       bs->buf_byte_idx--;
       if (bs->buf_byte_idx < 0)
          empty_buffer(bs, MINIMUM);
       bs->buf[bs->buf_byte_idx] = 0;
   }
   j -= k;
 }
}

/*write N bits byte aligned into the bit stream */
void byte_ali_putbits(bs, val, N)
Bit_stream_struc *bs;   /* bit stream structure */
unsigned int val;       /* val to write into the buffer */
int N;                  /* number of bits of val */
{
 unsigned long aligning;

 if (N > MAX_LENGTH)
    printf("Cannot read or write more than %d bits at a time.\n", MAX_LENGTH);
 aligning = sstell(bs)%8;
 if (aligning)
     putbits(bs, (unsigned int)0, (int)(8-aligning)); 

 putbits(bs, val, N);
}

/*read the next bute aligned N bits from the bit stream */
unsigned long byte_ali_getbits(bs, N)
Bit_stream_struc *bs;   /* bit stream structure */
int N;                  /* number of bits of val */
{
 unsigned long aligning;

 if (N > MAX_LENGTH)
    printf("Cannot read or write more than %d bits at a time.\n", MAX_LENGTH);
 aligning = sstell(bs)%8;
 if (aligning)
    getbits(bs, (int)(8-aligning));

 return(getbits(bs, N));
}

/*return the current bit stream length (in bits)*/
unsigned long sstell(bs)
Bit_stream_struc *bs;   /* bit stream structure */
{
  return(bs->totbit);
}

/*return the status of the bit stream*/
/* returns 1 if end of bit stream was reached */
/* returns 0 if end of bit stream was not reached */
int end_bs(bs)
Bit_stream_struc *bs;   /* bit stream structure */
{
  return(bs->eobs);
}

/*this function seeks for a byte aligned sync word in the bit stream and
  places the bit stream pointer right after the sync.
  This function returns 1 if the sync was found otherwise it returns 0  */
int seek_sync(bs, sync, N)
Bit_stream_struc *bs;   /* bit stream structure */
long sync;      /* sync word maximum 32 bits */
int N;          /* sync word length */
{
 unsigned long aligning;
 unsigned long val;
 long maxi = (int)pow(2.0, (FLOAT)N) - 1;

 aligning = sstell(bs)%ALIGNING;
 if (aligning)
    getbits(bs, (int)(ALIGNING-aligning));

  val = getbits(bs, N);
  while (((val&maxi) != sync) && (!end_bs(bs))) {
        val <<= ALIGNING;
        val |= getbits(bs, ALIGNING);
  }

 if (end_bs(bs)) return(0);
 else return(1);
}
/*****************************************************************************
*
*  End of bit_stream.c package
*
*****************************************************************************/

/*****************************************************************************
*
*  CRC error protection package
*
*****************************************************************************/

void I_CRC_calc(fr_ps, bit_alloc, crc)
frame_params *fr_ps;
unsigned int bit_alloc[2][SBLIMIT];
unsigned int *crc;
{
        int i, k;
        layer *info = fr_ps->header;
        int stereo  = fr_ps->stereo;
        int jsbound = fr_ps->jsbound;

        *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], 4, crc);
}

void II_CRC_calc(fr_ps, bit_alloc, scfsi, crc)
frame_params *fr_ps;
unsigned int bit_alloc[2][SBLIMIT], 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(data, length, crc)
unsigned int data, length, *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;
}

/*****************************************************************************
*
*  End of CRC error protection package
*
*****************************************************************************/