jcphuff.pas

用pascal寫的jpeg codec, 測試過的

Unit JcpHuff;

{ This file contains Huffman entropy encoding routines for progressive JPEG.

  We do not support output suspension in this module, since the library
  currently does not allow multiple-scan files to be written with output
  suspension. }

{ Original: jcphuff.c;  Copyright (C) 1995-1996, Thomas G. Lane. }

interface

uses
  jmorecfg,
  jinclude,
  jpeglib,
  jdeferr,
  jerror,
  jutils,
  jcomapi,
  jchuff;       	{ Declarations shared with jchuff.c }

{$I jconfig.inc}

{ Module initialization routine for progressive Huffman entropy encoding. }

{GLOBAL}
procedure jinit_phuff_encoder (cinfo : j_compress_ptr);

implementation

{ Expanded entropy encoder object for progressive Huffman encoding. }
type
  phuff_entropy_ptr = ^phuff_entropy_encoder;
  phuff_entropy_encoder = record
    pub : jpeg_entropy_encoder; { public fields }

    { Mode flag: TRUE for optimization, FALSE for actual data output }
    gather_statistics : boolean;

    { Bit-level coding status.
      next_output_byte/free_in_buffer are local copies of cinfo^.dest fields.}

    next_output_byte : JOCTETptr; { => next byte to write in buffer }
    free_in_buffer : size_t;    { # of byte spaces remaining in buffer }
    put_buffer : INT32;		{ current bit-accumulation buffer }
    put_bits : int;             { # of bits now in it }
    cinfo : j_compress_ptr;     { link to cinfo (needed for dump_buffer) }

    { Coding status for DC components }
    last_dc_val : array[0..MAX_COMPS_IN_SCAN-1] of int;
                                { last DC coef for each component }

    { Coding status for AC components }
    ac_tbl_no : int;            { the table number of the single component }
    EOBRUN : uInt;              { run length of EOBs }
    BE : uInt;                  { # of buffered correction bits before MCU }
    bit_buffer : JBytePtr;      { buffer for correction bits (1 per char) }
    { packing correction bits tightly would save some space but cost time... }

    restarts_to_go : uInt;	{ MCUs left in this restart interval }
    next_restart_num : int;     { next restart number to write (0-7) }

    { Pointers to derived tables (these workspaces have image lifespan).
      Since any one scan codes only DC or only AC, we only need one set
      of tables, not one for DC and one for AC. }

    derived_tbls : array[0..NUM_HUFF_TBLS-1] of c_derived_tbl_ptr;

    { Statistics tables for optimization; again, one set is enough }
    count_ptrs : array[0..NUM_HUFF_TBLS-1] of TLongTablePtr;
  end;


{ MAX_CORR_BITS is the number of bits the AC refinement correction-bit
  buffer can hold.  Larger sizes may slightly improve compression, but
  1000 is already well into the realm of overkill.
  The minimum safe size is 64 bits. }

const
  MAX_CORR_BITS = 1000;         { Max # of correction bits I can buffer }


{ Forward declarations }
{METHODDEF}
function encode_mcu_DC_first (cinfo : j_compress_ptr;
                              const MCU_data: array of JBLOCKROW) : boolean;
                              far; forward;
{METHODDEF}
function encode_mcu_AC_first (cinfo : j_compress_ptr;
                              const MCU_data: array of JBLOCKROW) : boolean;
                              far; forward;
{METHODDEF}
function encode_mcu_DC_refine (cinfo : j_compress_ptr;
                              const MCU_data: array of JBLOCKROW) : boolean;
                              far; forward;
{METHODDEF}
function encode_mcu_AC_refine (cinfo : j_compress_ptr;
                              const MCU_data: array of JBLOCKROW) : boolean;
                              far; forward;

{METHODDEF}
procedure finish_pass_phuff (cinfo : j_compress_ptr); far; forward;

{METHODDEF}
procedure finish_pass_gather_phuff (cinfo : j_compress_ptr); far; forward;


{ Initialize for a Huffman-compressed scan using progressive JPEG. }

{METHODDEF}
procedure start_pass_phuff (cinfo : j_compress_ptr;
                            gather_statistics : boolean); far;
var
  entropy : phuff_entropy_ptr;
  is_DC_band : boolean;
  ci, tbl : int;
  compptr : jpeg_component_info_ptr;
begin
  entropy := phuff_entropy_ptr (cinfo^.entropy);

  entropy^.cinfo := cinfo;
  entropy^.gather_statistics := gather_statistics;

  is_DC_band := (cinfo^.Ss = 0);

  { We assume jcmaster.c already validated the scan parameters. }

  { Select execution routines }
  if (cinfo^.Ah = 0) then
  begin
    if (is_DC_band) then
      entropy^.pub.encode_mcu := encode_mcu_DC_first
    else
      entropy^.pub.encode_mcu := encode_mcu_AC_first;
  end
  else
  begin
    if (is_DC_band) then
      entropy^.pub.encode_mcu := encode_mcu_DC_refine
    else
    begin
      entropy^.pub.encode_mcu := encode_mcu_AC_refine;
      { AC refinement needs a correction bit buffer }
      if (entropy^.bit_buffer = NIL) then
	entropy^.bit_buffer := JBytePtr(
	  cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
				      MAX_CORR_BITS * SIZEOF(byte)) );
    end;
  end;
  if (gather_statistics) then
    entropy^.pub.finish_pass := finish_pass_gather_phuff
  else
    entropy^.pub.finish_pass := finish_pass_phuff;

  { Only DC coefficients may be interleaved, so cinfo^.comps_in_scan = 1
    for AC coefficients. }

  for ci := 0 to pred(cinfo^.comps_in_scan) do
  begin
    compptr := cinfo^.cur_comp_info[ci];
    { Initialize DC predictions to 0 }
    entropy^.last_dc_val[ci] := 0;
    { Make sure requested tables are present }
    { (In gather mode, tables need not be allocated yet) }
    if (is_DC_band) then
    begin
      if (cinfo^.Ah <> 0) then          { DC refinement needs no table }
	continue;
      tbl := compptr^.dc_tbl_no;
      if (tbl < 0) or (tbl >= NUM_HUFF_TBLS) or
       ((cinfo^.dc_huff_tbl_ptrs[tbl] = NIL) and (not gather_statistics)) then
	ERREXIT1(j_common_ptr(cinfo),JERR_NO_HUFF_TABLE, tbl);
    end
    else
    begin
      tbl := compptr^.ac_tbl_no;
      entropy^.ac_tbl_no := tbl;
      if (tbl < 0) or (tbl >= NUM_HUFF_TBLS) or
       ((cinfo^.ac_huff_tbl_ptrs[tbl] = NIL) and (not gather_statistics)) then
        ERREXIT1(j_common_ptr(cinfo),JERR_NO_HUFF_TABLE, tbl);
    end;
    if (gather_statistics) then
    begin
      { Allocate and zero the statistics tables }
      { Note that jpeg_gen_optimal_table expects 257 entries in each table! }
      if (entropy^.count_ptrs[tbl] = NIL) then
	entropy^.count_ptrs[tbl] := TLongTablePtr(
	  cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
				      257 * SIZEOF(long)) );
      MEMZERO(entropy^.count_ptrs[tbl], 257 * SIZEOF(long));
    end
    else
    begin
      { Compute derived values for Huffman tables }
      { We may do this more than once for a table, but it's not expensive }
      if (is_DC_band) then
        jpeg_make_c_derived_tbl(cinfo, cinfo^.dc_huff_tbl_ptrs[tbl]^,
				 entropy^.derived_tbls[tbl])
      else
        jpeg_make_c_derived_tbl(cinfo, cinfo^.ac_huff_tbl_ptrs[tbl]^,
				 entropy^.derived_tbls[tbl]);
    end;
  end;

  { Initialize AC stuff }
  entropy^.EOBRUN := 0;
  entropy^.BE := 0;

  { Initialize bit buffer to empty }
  entropy^.put_buffer := 0;
  entropy^.put_bits := 0;

  { Initialize restart stuff }
  entropy^.restarts_to_go := cinfo^.restart_interval;
  entropy^.next_restart_num := 0;
end;




{LOCAL}
procedure dump_buffer (entropy : phuff_entropy_ptr);
{ Empty the output buffer; we do not support suspension in this module. }
var
  dest : jpeg_destination_mgr_ptr;
begin
  dest := entropy^.cinfo^.dest;

  if (not dest^.empty_output_buffer (entropy^.cinfo)) then
    ERREXIT(j_common_ptr(entropy^.cinfo), JERR_CANT_SUSPEND);
  { After a successful buffer dump, must reset buffer pointers }
  entropy^.next_output_byte := dest^.next_output_byte;
  entropy^.free_in_buffer := dest^.free_in_buffer;
end;


{ Outputting bits to the file }

{ Only the right 24 bits of put_buffer are used; the valid bits are
  left-justified in this part.  At most 16 bits can be passed to emit_bits
  in one call, and we never retain more than 7 bits in put_buffer
  between calls, so 24 bits are sufficient. }


{LOCAL}
procedure emit_bits (entropy : phuff_entropy_ptr;
                     code : uInt;
                     size : int); {INLINE}
{ Emit some bits, unless we are in gather mode }
var
  {register} put_buffer : INT32;
  {register} put_bits : int;
var
  c : int;
begin
  { This routine is heavily used, so it's worth coding tightly. }
  put_buffer := INT32 (code);
  put_bits := entropy^.put_bits;

  { if size is 0, caller used an invalid Huffman table entry }
  if (size = 0) then
    ERREXIT(j_common_ptr(entropy^.cinfo), JERR_HUFF_MISSING_CODE);

  if (entropy^.gather_statistics) then
    exit;			{ do nothing if we're only getting stats }

  put_buffer := put_buffer and ((INT32(1) shl size) - 1);
                                { mask off any extra bits in code }

  Inc(put_bits, size);          { new number of bits in buffer }

  put_buffer := put_buffer shl (24 - put_bits); { align incoming bits }

  put_buffer := put_buffer or entropy^.put_buffer;
                                { and merge with old buffer contents }

  while (put_bits >= 8) do
  begin
    c := int ((put_buffer shr 16) and $FF);

    {emit_byte(entropy, c);}
    { Outputting bytes to the file.
      NB: these must be called only when actually outputting,
      that is, entropy^.gather_statistics = FALSE. }
    { Emit a byte }
    entropy^.next_output_byte^ := JOCTET(c);
    Inc(entropy^.next_output_byte);
    Dec(entropy^.free_in_buffer);
    if (entropy^.free_in_buffer = 0) then
      dump_buffer(entropy);

    if (c = $FF) then
    begin		{ need to stuff a zero byte? }
      {emit_byte(entropy, 0);}
      entropy^.next_output_byte^ := JOCTET(0);
      Inc(entropy^.next_output_byte);
      Dec(entropy^.free_in_buffer);
      if (entropy^.free_in_buffer = 0) then
        dump_buffer(entropy);
    end;
    put_buffer := put_buffer shl 8;
    Dec(put_bits, 8);
  end;

  entropy^.put_buffer := put_buffer; { update variables }
  entropy^.put_bits := put_bits;
end;


{LOCAL}
procedure flush_bits (entropy : phuff_entropy_ptr);
begin
  emit_bits(entropy, $7F, 7); { fill any partial byte with ones }
  entropy^.put_buffer := 0;     { and reset bit-buffer to empty }
  entropy^.put_bits := 0;
end;

{ Emit (or just count) a Huffman symbol. }


{LOCAL}
procedure emit_symbol (entropy : phuff_entropy_ptr;
                       tbl_no : int;
                       symbol : int); {INLINE}
var
  tbl : c_derived_tbl_ptr;
begin
  if (entropy^.gather_statistics) then
    Inc(entropy^.count_ptrs[tbl_no]^[symbol])
  else
  begin
    tbl := entropy^.derived_tbls[tbl_no];
    emit_bits(entropy, tbl^.ehufco[symbol], tbl^.ehufsi[symbol]);
  end;
end;


{ Emit bits from a correction bit buffer. }

{LOCAL}
procedure emit_buffered_bits (entropy : phuff_entropy_ptr;
                              bufstart : JBytePtr;
		              nbits : uInt);
var
  bufptr : byteptr;
begin
  if (entropy^.gather_statistics) then
    exit;			{ no real work }

  bufptr := byteptr(bufstart);
  while (nbits > 0) do
  begin
    emit_bits(entropy, uInt(bufptr^), 1);
    Inc(bufptr);
    Dec(nbits);
  end;
end;


{ Emit any pending EOBRUN symbol. }

{LOCAL}
procedure emit_eobrun (entropy : phuff_entropy_ptr);
var
  {register} temp, nbits : int;
begin
  if (entropy^.EOBRUN > 0) then
  begin	                       { if there is any pending EOBRUN }
    temp := entropy^.EOBRUN;
    nbits := 0;
    temp := temp shr 1;
    while (temp <> 0) do
    begin
      Inc(nbits);
      temp := temp shr 1;
    end;

    emit_symbol(entropy, entropy^.ac_tbl_no, nbits shl 4);
    if (nbits <> 0) then
      emit_bits(entropy, entropy^.EOBRUN, nbits);

    entropy^.EOBRUN := 0;

    { Emit any buffered correction bits }
    emit_buffered_bits(entropy, entropy^.bit_buffer, entropy^.BE);
    entropy^.BE := 0;
  end;
end;


{ Emit a restart marker & resynchronize predictions. }

{LOCAL}
procedure emit_restart (entropy : phuff_entropy_ptr;
                        restart_num : int);
var
  ci : int;
begin
  emit_eobrun(entropy);

  if (not entropy^.gather_statistics) then
  begin
    flush_bits(entropy);
    {emit_byte(entropy, $FF);}
    { Outputting bytes to the file.
      NB: these must be called only when actually outputting,
      that is, entropy^.gather_statistics = FALSE. }

    entropy^.next_output_byte^ := JOCTET($FF);
    Inc(entropy^.next_output_byte);
    Dec(entropy^.free_in_buffer);
    if (entropy^.free_in_buffer = 0) then
      dump_buffer(entropy);

    {emit_byte(entropy, JPEG_RST0 + restart_num);}
    entropy^.next_output_byte^ := JOCTET(JPEG_RST0 + restart_num);
    Inc(entropy^.next_output_byte);
    Dec(entropy^.free_in_buffer);
    if (entropy^.free_in_buffer = 0) then
      dump_buffer(entropy);
  end;

  if (entropy^.cinfo^.Ss = 0) then
  begin
    { Re-initialize DC predictions to 0 }
    for ci := 0 to pred(entropy^.cinfo^.comps_in_scan) do
      entropy^.last_dc_val[ci] := 0;
  end
  else
  begin
    { Re-initialize all AC-related fields to 0 }
    entropy^.EOBRUN := 0;
    entropy^.BE := 0;
  end;
end;


{ MCU encoding for DC initial scan (either spectral selection,
  or first pass of successive approximation). }

{METHODDEF}
function encode_mcu_DC_first (cinfo : j_compress_ptr;
                              const MCU_data: array of JBLOCKROW) : boolean;
var
  entropy : phuff_entropy_ptr;
  {register} temp, temp2 : int;
  {register} nbits : int;
  blkn, ci : int;
  Al : int;
  block : JBLOCK_PTR;
  compptr : jpeg_component_info_ptr;
  ishift_temp : int;
begin
  entropy := phuff_entropy_ptr (cinfo^.entropy);
  Al := cinfo^.Al;

  entropy^.next_output_byte := cinfo^.dest^.next_output_byte;
  entropy^.free_in_buffer := cinfo^.dest^.free_in_buffer;

  { Emit restart marker if needed }
  if (cinfo^.restart_interval <> 0) then
    if (entropy^.restarts_to_go = 0) then
      emit_restart(entropy, entropy^.next_restart_num);

  { Encode the MCU data blocks }
  for blkn := 0 to pred(cinfo^.blocks_in_MCU) do
  begin
    block := JBLOCK_PTR(MCU_data[blkn]);
    ci := cinfo^.MCU_membership[blkn];
    compptr := cinfo^.cur_comp_info[ci];

    { Compute the DC value after the required point transform by Al.
      This is simply an arithmetic right shift. }

    {temp2 := IRIGHT_SHIFT( int(block^[0]), Al);}
    {IRIGHT_SHIFT_IS_UNSIGNED}
    ishift_temp := int(block^[0]);