jdhuff.pas

DELPHI版的JPEG文件解码源程序

  { include any full bytes in next_marker's count of discarded bytes }
  Inc(cinfo^.marker^.discarded_bytes, entropy^.bitstate.bits_left div 8);
  entropy^.bitstate.bits_left := 0;

  { Advance past the RSTn marker }
  if (not cinfo^.marker^.read_restart_marker (cinfo)) then
  begin
    process_restart := FALSE;
    exit;
  end;

  { Re-initialize DC predictions to 0 }
  for ci := 0 to pred(cinfo^.comps_in_scan) do
    entropy^.saved.last_dc_val[ci] := 0;

  { Reset restart counter }
  entropy^.restarts_to_go := cinfo^.restart_interval;

  { Reset out-of-data flag, unless read_restart_marker left us smack up
    against a marker.  In that case we will end up treating the next data
    segment as empty, and we can avoid producing bogus output pixels by
    leaving the flag set. }

  if (cinfo^.unread_marker = 0) then
    entropy^.pub.insufficient_data := FALSE;

  process_restart := TRUE;
end;


{ Decode and return one MCU's worth of Huffman-compressed coefficients.
  The coefficients are reordered from zigzag order into natural array order,
  but are not dequantized.

  The i'th block of the MCU is stored into the block pointed to by
  MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
  (Wholesale zeroing is usually a little faster than retail...)

  Returns FALSE if data source requested suspension.  In that case no
  changes have been made to permanent state.  (Exception: some output
  coefficients may already have been assigned.  This is harmless for
  this module, since we'll just re-assign them on the next call.) }

{METHODDEF}
function decode_mcu (cinfo : j_decompress_ptr;
                     var MCU_data : array of JBLOCKROW) : boolean; far;
label
  label1, label2, label3;
var
  entropy : huff_entropy_ptr;
  {register} s, k, r : int;
  blkn, ci : int;
  block : JBLOCK_PTR;
  {BITREAD_STATE_VARS}
  get_buffer : bit_buf_type ; {register}
  bits_left : int; {register}
  br_state : bitread_working_state;

  state : savable_state;
  dctbl : d_derived_tbl_ptr;
  actbl : d_derived_tbl_ptr;
var
  nb, look : int; {register}
begin
  entropy := huff_entropy_ptr (cinfo^.entropy);

  { Process restart marker if needed; may have to suspend }
  if (cinfo^.restart_interval <> 0) then
  begin
    if (entropy^.restarts_to_go = 0) then
      if (not process_restart(cinfo)) then
      begin
        decode_mcu := FALSE;
        exit;
      end;
  end;

  { If we've run out of data, just leave the MCU set to zeroes.
    This way, we return uniform gray for the remainder of the segment. }

  if not entropy^.pub.insufficient_data then
  begin

    { Load up working state }
    {BITREAD_LOAD_STATE(cinfo,entropy^.bitstate);}
    br_state.cinfo := cinfo;
    br_state.next_input_byte := cinfo^.src^.next_input_byte;
    br_state.bytes_in_buffer := cinfo^.src^.bytes_in_buffer;
    get_buffer := entropy^.bitstate.get_buffer;
    bits_left := entropy^.bitstate.bits_left;

    {ASSIGN_STATE(state, entropy^.saved);}
    state := entropy^.saved;

    { Outer loop handles each block in the MCU }

    for blkn := 0 to pred(cinfo^.blocks_in_MCU) do
    begin
      block := JBLOCK_PTR(MCU_data[blkn]);
      dctbl := entropy^.dc_cur_tbls[blkn];
      actbl := entropy^.ac_cur_tbls[blkn];

      { Decode a single block's worth of coefficients }

      { Section F.2.2.1: decode the DC coefficient difference }
      {HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);}
      if (bits_left < HUFF_LOOKAHEAD) then
      begin
        if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
        begin
          decode_mcu := False;
          exit;
        end;
        get_buffer := br_state.get_buffer;
        bits_left := br_state.bits_left;
        if (bits_left < HUFF_LOOKAHEAD) then
        begin
          nb := 1;
          goto label1;
        end;
      end;
      {look := PEEK_BITS(HUFF_LOOKAHEAD);}
      look := int(get_buffer shr (bits_left -  HUFF_LOOKAHEAD)) and
                   pred(1 shl HUFF_LOOKAHEAD);

      nb := dctbl^.look_nbits[look];
      if (nb <> 0) then
      begin
        {DROP_BITS(nb);}
        Dec(bits_left, nb);

        s := dctbl^.look_sym[look];
      end
      else
      begin
        nb := HUFF_LOOKAHEAD+1;
    label1:
        s := jpeg_huff_decode(br_state,get_buffer,bits_left,dctbl,nb);
        if (s < 0) then
        begin
          decode_mcu := FALSE;
          exit;
        end;
        get_buffer := br_state.get_buffer;
        bits_left := br_state.bits_left;
      end;

      if (s <> 0) then
      begin
        {CHECK_BIT_BUFFER(br_state, s, return FALSE);}
        if (bits_left < s) then
        begin
          if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
          begin
            decode_mcu := FALSE;
            exit;
          end;
          get_buffer := br_state.get_buffer;
          bits_left := br_state.bits_left;
        end;

        {r := GET_BITS(s);}
        Dec(bits_left, s);
        r := ( int(get_buffer shr bits_left)) and ( pred(1 shl s) );

        {s := HUFF_EXTEND(r, s);}
        if (r < extend_test[s]) then
          s := r + extend_offset[s]
        else
          s := r;
      end;

      if (entropy^.dc_needed[blkn]) then
      begin
	{ Convert DC difference to actual value, update last_dc_val }
        ci := cinfo^.MCU_membership[blkn];
	Inc(s, state.last_dc_val[ci]);
        state.last_dc_val[ci] := s;
        { Output the DC coefficient (assumes jpeg_natural_order[0] := 0) }
        block^[0] := JCOEF (s);
      end;

      if (entropy^.ac_needed[blkn]) then
      begin

	{ Section F.2.2.2: decode the AC coefficients }
	{ Since zeroes are skipped, output area must be cleared beforehand }
	k := 1;
        while (k < DCTSIZE2) do         { Nomssi: k is incr. in the loop }
        begin
          {HUFF_DECODE(s, br_state, actbl, return FALSE, label2);}
          if (bits_left < HUFF_LOOKAHEAD) then
          begin
            if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
            begin
              decode_mcu := False;
              exit;
            end;
            get_buffer := br_state.get_buffer;
            bits_left := br_state.bits_left;
            if (bits_left < HUFF_LOOKAHEAD) then
            begin
              nb := 1;
              goto label2;
            end;
          end;
          {look := PEEK_BITS(HUFF_LOOKAHEAD);}
          look := int(get_buffer shr (bits_left -  HUFF_LOOKAHEAD)) and
                       pred(1 shl HUFF_LOOKAHEAD);

          nb := actbl^.look_nbits[look];
          if (nb <> 0) then
          begin
            {DROP_BITS(nb);}
            Dec(bits_left, nb);

            s := actbl^.look_sym[look];
          end
          else
          begin
            nb := HUFF_LOOKAHEAD+1;
        label2:
            s := jpeg_huff_decode(br_state,get_buffer,bits_left,actbl,nb);
            if (s < 0) then
            begin
              decode_mcu := FALSE;
              exit;
            end;
            get_buffer := br_state.get_buffer;
            bits_left := br_state.bits_left;
          end;

	  r := s shr 4;
	  s := s and 15;

          if (s <> 0) then
          begin
            Inc(k, r);
            {CHECK_BIT_BUFFER(br_state, s, return FALSE);}
            if (bits_left < s) then
            begin
              if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
              begin
                decode_mcu := FALSE;
                exit;
              end;
              get_buffer := br_state.get_buffer;
              bits_left := br_state.bits_left;
            end;

            {r := GET_BITS(s);}
            Dec(bits_left, s);
            r := (int(get_buffer shr bits_left)) and ( pred(1 shl s) );

            {s := HUFF_EXTEND(r, s);}
            if (r < extend_test[s]) then
              s := r + extend_offset[s]
            else
              s := r;
            { Output coefficient in natural (dezigzagged) order.
              Note: the extra entries in jpeg_natural_order[] will save us
              if k >= DCTSIZE2, which could happen if the data is corrupted. }

            block^[jpeg_natural_order[k]] := JCOEF (s);
          end
          else
          begin
            if (r <> 15) then
              break;
            Inc(k, 15);
          end;
          Inc(k);
        end;
      end
      else
      begin

        { Section F.2.2.2: decode the AC coefficients }
        { In this path we just discard the values }
        k := 1;
        while (k < DCTSIZE2) do
        begin
	  {HUFF_DECODE(s, br_state, actbl, return FALSE, label3);}
          if (bits_left < HUFF_LOOKAHEAD) then
          begin
            if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
            begin
              decode_mcu := False;
              exit;
            end;
            get_buffer := br_state.get_buffer;
            bits_left := br_state.bits_left;
            if (bits_left < HUFF_LOOKAHEAD) then
            begin
              nb := 1;
              goto label3;
            end;
          end;
          {look := PEEK_BITS(HUFF_LOOKAHEAD);}
          look := int(get_buffer shr (bits_left -  HUFF_LOOKAHEAD)) and
                       pred(1 shl HUFF_LOOKAHEAD);

          nb := actbl^.look_nbits[look];
          if (nb <> 0) then
          begin
            {DROP_BITS(nb);}
	    Dec(bits_left, nb);

            s := actbl^.look_sym[look];
          end
          else
          begin
            nb := HUFF_LOOKAHEAD+1;
        label3:
            s := jpeg_huff_decode(br_state,get_buffer,bits_left,actbl,nb);
            if (s < 0) then
            begin
              decode_mcu := FALSE;
              exit;
            end;
            get_buffer := br_state.get_buffer;
            bits_left := br_state.bits_left;
          end;

	  r := s shr 4;
	  s := s and 15;

	  if (s <> 0) then
          begin
	    Inc(k, r);
	    {CHECK_BIT_BUFFER(br_state, s, return FALSE);}
            if (bits_left < s) then
            begin
              if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
              begin
                decode_mcu := FALSE;
                exit;
              end;
              get_buffer := br_state.get_buffer;
              bits_left := br_state.bits_left;
            end;

	    {DROP_BITS(s);}
            Dec(bits_left, s);
	  end
          else
          begin
	    if (r <> 15) then
	      break;
	    Inc(k, 15);
	  end;
          Inc(k);
        end;

      end;
    end;

    { Completed MCU, so update state }
    {BITREAD_SAVE_STATE(cinfo,entropy^.bitstate);}
    cinfo^.src^.next_input_byte := br_state.next_input_byte;
    cinfo^.src^.bytes_in_buffer := br_state.bytes_in_buffer;
    entropy^.bitstate.get_buffer := get_buffer;
    entropy^.bitstate.bits_left := bits_left;

    {ASSIGN_STATE(entropy^.saved, state);}
    entropy^.saved := state;

  end;

  { Account for restart interval (no-op if not using restarts) }
  Dec(entropy^.restarts_to_go);

  decode_mcu := TRUE;
end;


{ Module initialization routine for Huffman entropy decoding. }

{GLOBAL}
procedure jinit_huff_decoder (cinfo : j_decompress_ptr);
var
  entropy : huff_entropy_ptr;
  i : int;
begin
  entropy := huff_entropy_ptr(
    cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
				SIZEOF(huff_entropy_decoder)) );
  cinfo^.entropy := jpeg_entropy_decoder_ptr (entropy);
  entropy^.pub.start_pass := start_pass_huff_decoder;
  entropy^.pub.decode_mcu := decode_mcu;

  { Mark tables unallocated }
  for i := 0 to pred(NUM_HUFF_TBLS) do
  begin
    entropy^.dc_derived_tbls[i] := NIL;
    entropy^.ac_derived_tbls[i] := NIL;
  end;
end;

end.