jdphuff.c

MPEG4解码源代码(包含完整的工程文件)

    /* Section F.2.2.1: decode the DC coefficient difference */
    HUFF_DECODE(s, br_state, tbl, return FALSE, label1);
    if (s) {
      CHECK_BIT_BUFFER(br_state, s, return FALSE);
      r = GET_BITS(s);
      s = HUFF_EXTEND(r, s);
    }

    /* Convert DC difference to actual value, update last_dc_val */
    s += state.last_dc_val[ci];
    state.last_dc_val[ci] = s;
    /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
    (*block)[0] = (JCOEF) (s << Al);
  }

  /* Completed MCU, so update state */
  BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
  ASSIGN_STATE(entropy->saved, state);

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for AC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF(boolean)
decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{   
  phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
  int Se = cinfo->Se;
  int Al = cinfo->Al;
  register int s, k, r;
  unsigned int EOBRUN;
  JBLOCKROW block;
  BITREAD_STATE_VARS;
  d_derived_tbl * tbl;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
	return FALSE;
  }

  /* Load up working state.
   * We can avoid loading/saving bitread state if in an EOB run.
   */
  EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we care about */

  /* There is always only one block per MCU */

  if (EOBRUN > 0)		/* if it's a band of zeroes... */
    EOBRUN--;			/* ...process it now (we do nothing) */
  else {
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    block = MCU_data[0];
    tbl = entropy->ac_derived_tbl;

    for (k = cinfo->Ss; k <= Se; k++) {
      HUFF_DECODE(s, br_state, tbl, return FALSE, label2);
      r = s >> 4;
      s &= 15;
      if (s) {
        k += r;
        CHECK_BIT_BUFFER(br_state, s, return FALSE);
        r = GET_BITS(s);
        s = HUFF_EXTEND(r, s);
	/* Scale and output coefficient in natural (dezigzagged) order */
        (*block)[jpeg_natural_order[k]] = (JCOEF) (s << Al);
      } else {
        if (r == 15) {		/* ZRL */
          k += 15;		/* skip 15 zeroes in band */
        } else {		/* EOBr, run length is 2^r + appended bits */
          EOBRUN = 1 << r;
          if (r) {		/* EOBr, r > 0 */
	    CHECK_BIT_BUFFER(br_state, r, return FALSE);
            r = GET_BITS(r);
            EOBRUN += r;
          }
	  EOBRUN--;		/* this band is processed at this moment */
	  break;		/* force end-of-band */
	}
      }
    }

    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
  }

  /* Completed MCU, so update state */
  entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we care about */

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for DC successive approximation refinement scan.
 * Note: we assume such scans can be multi-component, although the spec
 * is not very clear on the point.
 */

METHODDEF(boolean)
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{   
  phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
  int p1 = 1 << cinfo->Al;	/* 1 in the bit position being coded */
  int blkn;
  JBLOCKROW block;
  BITREAD_STATE_VARS;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
	return FALSE;
  }

  /* Load up working state */
  BITREAD_LOAD_STATE(cinfo,entropy->bitstate);

  /* Outer loop handles each block in the MCU */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    block = MCU_data[blkn];

    /* Encoded data is simply the next bit of the two's-complement DC value */
    CHECK_BIT_BUFFER(br_state, 1, return FALSE);
    if (GET_BITS(1))
      (*block)[0] |= p1;
    /* Note: since we use |=, repeating the assignment later is safe */
  }

  /* Completed MCU, so update state */
  BITREAD_SAVE_STATE(cinfo,entropy->bitstate);

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for AC successive approximation refinement scan.
 */

METHODDEF(boolean)
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{   
  phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
  int Se = cinfo->Se;
  int p1 = 1 << cinfo->Al;	/* 1 in the bit position being coded */
  int m1 = (-1) << cinfo->Al;	/* -1 in the bit position being coded */
  register int s, k, r;
  unsigned int EOBRUN;
  JBLOCKROW block;
  JCOEFPTR thiscoef;
  BITREAD_STATE_VARS;
  d_derived_tbl * tbl;
  int num_newnz;
  int newnz_pos[DCTSIZE2];

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
	return FALSE;
  }

  /* Load up working state */
  BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
  EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we care about */

  /* There is always only one block per MCU */
  block = MCU_data[0];
  tbl = entropy->ac_derived_tbl;

  /* If we are forced to suspend, we must undo the assignments to any newly
   * nonzero coefficients in the block, because otherwise we'd get confused
   * next time about which coefficients were already nonzero.
   * But we need not undo addition of bits to already-nonzero coefficients;
   * instead, we can test the current bit position to see if we already did it.
   */
  num_newnz = 0;

  /* initialize coefficient loop counter to start of band */
  k = cinfo->Ss;

  if (EOBRUN == 0) {
    for (; k <= Se; k++) {
      HUFF_DECODE(s, br_state, tbl, goto undoit, label3);
      r = s >> 4;
      s &= 15;
      if (s) {
	if (s != 1)		/* size of new coef should always be 1 */
	  WARNMS(cinfo, JWRN_HUFF_BAD_CODE);
        CHECK_BIT_BUFFER(br_state, 1, goto undoit);
        if (GET_BITS(1))
	  s = p1;		/* newly nonzero coef is positive */
	else
	  s = m1;		/* newly nonzero coef is negative */
      } else {
	if (r != 15) {
	  EOBRUN = 1 << r;	/* EOBr, run length is 2^r + appended bits */
	  if (r) {
	    CHECK_BIT_BUFFER(br_state, r, goto undoit);
	    r = GET_BITS(r);
	    EOBRUN += r;
	  }
	  break;		/* rest of block is handled by EOB logic */
	}
	/* note s = 0 for processing ZRL */
      }
      /* Advance over already-nonzero coefs and r still-zero coefs,
       * appending correction bits to the nonzeroes.  A correction bit is 1
       * if the absolute value of the coefficient must be increased.
       */
      do {
	thiscoef = *block + jpeg_natural_order[k];
	if (*thiscoef != 0) {
	  CHECK_BIT_BUFFER(br_state, 1, goto undoit);
	  if (GET_BITS(1)) {
	    if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */
	      if (*thiscoef >= 0)
		*thiscoef += p1;
	      else
		*thiscoef += m1;
	    }
	  }
	} else {
	  if (--r < 0)
	    break;		/* reached target zero coefficient */
	}
	k++;
      } while (k <= Se);
      if (s) {
	int pos = jpeg_natural_order[k];
	/* Output newly nonzero coefficient */
	(*block)[pos] = (JCOEF) s;
	/* Remember its position in case we have to suspend */
	newnz_pos[num_newnz++] = pos;
      }
    }
  }

  if (EOBRUN > 0) {
    /* Scan any remaining coefficient positions after the end-of-band
     * (the last newly nonzero coefficient, if any).  Append a correction
     * bit to each already-nonzero coefficient.  A correction bit is 1
     * if the absolute value of the coefficient must be increased.
     */
    for (; k <= Se; k++) {
      thiscoef = *block + jpeg_natural_order[k];
      if (*thiscoef != 0) {
	CHECK_BIT_BUFFER(br_state, 1, goto undoit);
	if (GET_BITS(1)) {
	  if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */
	    if (*thiscoef >= 0)
	      *thiscoef += p1;
	    else
	      *thiscoef += m1;
	  }
	}
      }
    }
    /* Count one block completed in EOB run */
    EOBRUN--;
  }

  /* Completed MCU, so update state */
  BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
  entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we care about */

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;

undoit:
  /* Re-zero any output coefficients that we made newly nonzero */
  while (num_newnz > 0)
    (*block)[newnz_pos[--num_newnz]] = 0;

  return FALSE;
}


/*
 * Module initialization routine for progressive Huffman entropy decoding.
 */

GLOBAL(void)
jinit_phuff_decoder (j_decompress_ptr cinfo)
{
  phuff_entropy_ptr entropy;
  int *coef_bit_ptr;
  int ci, i;

  entropy = (phuff_entropy_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				SIZEOF(phuff_entropy_decoder));
  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
  entropy->pub.start_pass = start_pass_phuff_decoder;

  /* Mark derived tables unallocated */
  for (i = 0; i < NUM_HUFF_TBLS; i++) {
    entropy->derived_tbls[i] = NULL;
  }

  /* Create progression status table */
  cinfo->coef_bits = (int (*)[DCTSIZE2])
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				cinfo->num_components*DCTSIZE2*SIZEOF(int));
  coef_bit_ptr = & cinfo->coef_bits[0][0];
  for (ci = 0; ci < cinfo->num_components; ci++) 
    for (i = 0; i < DCTSIZE2; i++)
      *coef_bit_ptr++ = -1;
}

#endif /* D_PROGRESSIVE_SUPPORTED */