数据压缩 -- 源码

implementation

TYPE
{$IFDEF WIN32}
  TwoByteInt  = SmallInt;
{$ELSE}
  TwoByteInt  = Integer;
{$ENDIF}
  PWord=^TWord;
  TWord=ARRAY[0..32759]OF TwoByteInt;
  PByte=^TByte;
  TByte=ARRAY[0..65519]OF Byte;

CONST
(*
NOTE :
   The following constants are set to the values used by LHArc.
   You can change three of them as follows :

   DICBIT : Lempel-Ziv dictionnary size.
   Lowering this constant can lower the compression efficiency a lot !
   But increasing it (on a 32 bit platform only, i.e. Delphi 2) will not yield
   noticeably better results.
   If you set DICBIT to 15 or more, set PBIT to 5; and if you set DICBIT to 19
   or more, set NPT to NP, too.

   WINBIT : Sliding window size.
   The compression ratio depends a lot of this value.
   You can increase it to 15 to get better results on large files.
   I recommend doing this if you have enough memory, except if you want that
   your compressed data remain compatible with LHArc.
   On a 32 bit platform, you can increase it to 16. Using a larger value will
   only waste time and memory.

   BUFBIT : I/O Buffer size. You can lower it to save memory, or increase it
   to reduce disk access.
*)

  BITBUFSIZ=16;
  UCHARMAX=255;

  DICBIT=13;
  DICSIZ=1 SHL DICBIT;

  MATCHBIT=8;
  MAXMATCH=1 SHL MATCHBIT;
  THRESHOLD=3;
  PERCFLAG=$8000;

  NC=(UCHARMAX+MAXMATCH+2-THRESHOLD);
  CBIT=9;
  CODEBIT=16;

  NP=DICBIT+1;
  NT=CODEBIT+3;
  PBIT=4; {Log2(NP)}
  TBIT=5; {Log2(NT)}
  NPT=NT; {Greater from NP and NT}

  NUL=0;
  MAXHASHVAL=(3*DICSIZ+(DICSIZ SHR 9+1)*UCHARMAX);

  WINBIT=14;
  WINDOWSIZE=1 SHL WINBIT;

  BUFBIT=13;
  BUFSIZE=1 SHL BUFBIT;

TYPE
  BufferArray = ARRAY[0..PRED(BUFSIZE)]OF Byte;
  LeftRightArray = ARRAY[0..2*(NC-1)]OF Word;
  CTableArray = ARRAY[0..4095]OF Word;
  CLenArray = ARRAY[0..PRED(NC)]OF Byte;
  HeapArray = ARRAY[0..NC]OF Word;

VAR
  OrigSize,CompSize:Longint;
  InFile,OutFile:TStream;

  BitBuf:Word;
  n,HeapSize:TwoByteInt;
  SubBitBuf,BitCount:Word;

  Buffer:^BufferArray;
  BufPtr:Word;

  Left,Right:^LeftRightArray;

  PtTable:ARRAY[0..255]OF Word;
  PtLen:ARRAY[0..PRED(NPT)]OF Byte;
  CTable:^CTableArray;
  CLen:^CLenArray;

  BlockSize:Word;

  { The following variables are used by the compression engine only }

  Heap:^HeapArray;
  LenCnt:ARRAY[0..16]OF Word;

  Freq,SortPtr:PWord;
  Len:PByte;
  Depth:Word;

  Buf:PByte;

  CFreq:ARRAY[0..2*(NC-1)]OF Word;
  PFreq:ARRAY[0..2*(NP-1)]OF Word;
  TFreq:ARRAY[0..2*(NT-1)]OF Word;

  CCode:ARRAY[0..PRED(NC)]OF Word;
  PtCode:ARRAY[0..PRED(NPT)]OF Word;

  CPos,OutputPos,OutputMask:Word;
  Text,ChildCount:PByte;

  Pos,MatchPos,Avail:Word;
  Position,Parent,Prev,Next:PWord;

  Remainder,MatchLen:TwoByteInt;
  Level:PByte;

{********************************** File I/O **********************************}

FUNCTION GetC:Byte;
BEGIN
  IF BufPtr=0 THEN
    InFile.Read(Buffer^,BUFSIZE);
  GetC:=Buffer^[BufPtr];BufPtr:=SUCC(BufPtr)AND PRED(BUFSIZE);
END;

PROCEDURE PutC(c:Byte);
BEGIN
  IF BufPtr=BUFSIZE THEN
    BEGIN
      OutFile.Write(Buffer^,BUFSIZE);BufPtr:=0;
    END;
  Buffer^[BufPtr]:=C;INC(BufPtr);
END;

FUNCTION BRead(p:POINTER;n:TwoByteInt):TwoByteInt;
BEGIN
  BRead := InFile.Read(p^,n);
END;

PROCEDURE BWrite(p:POINTER;n:TwoByteInt);
BEGIN
  OutFile.Write(p^,n);
END;

{**************************** Bit handling routines ***************************}

PROCEDURE FillBuf(n:TwoByteInt);
BEGIN
  BitBuf:=(BitBuf SHL n);
  WHILE n>BitCount DO BEGIN
    DEC(n,BitCount);
    BitBuf:=BitBuf OR (SubBitBuf SHL n);
    IF (CompSize<>0) THEN
      BEGIN
        DEC(CompSize);SubBitBuf:=GetC;
      END ELSE
        SubBitBuf:=0;
    BitCount:=8;
  END;
  DEC(BitCount,n);
  BitBuf:=BitBuf OR (SubBitBuf SHR BitCount);
END;

FUNCTION GetBits(n:TwoByteInt):Word;
BEGIN
  GetBits:=BitBuf SHR (BITBUFSIZ-n);
  FillBuf(n);
END;

PROCEDURE PutBits(n:TwoByteInt;x:Word);
BEGIN
  IF n<BitCount THEN
    BEGIN
      DEC(BitCount,n);
      SubBitBuf:=SubBitBuf OR (x SHL BitCount);
    END ELSE BEGIN
      DEC(n,BitCount);
      PutC(SubBitBuf OR (x SHR n));INC(CompSize);
      IF n<8 THEN
        BEGIN
          BitCount:=8-n;SubBitBuf:=x SHL BitCount;
        END ELSE BEGIN
          PutC(x SHR (n-8));INC(CompSize);
          BitCount:=16-n;SubBitBuf:=x SHL BitCount;
        END;
    END;
END;

PROCEDURE InitGetBits;
BEGIN
  BitBuf:=0;SubBitBuf:=0;BitCount:=0;FillBuf(BITBUFSIZ);
END;

PROCEDURE InitPutBits;
BEGIN
  BitCount:=8;SubBitBuf:=0;
END;

{******************************** Decompression *******************************}

PROCEDURE MakeTable(nchar:TwoByteInt;BitLen:PByte;TableBits:TwoByteInt;Table:PWord);
VAR
  count,weight:ARRAY[1..16]OF Word;
  start:ARRAY[1..17]OF Word;
  p:PWord;
  i,k,Len,ch,jutbits,Avail,nextCode,mask:TwoByteInt;
BEGIN
  FOR i:=1 TO 16 DO
    count[i]:=0;
  FOR i:=0 TO PRED(nchar) DO
    INC(count[BitLen^[i]]);
  start[1]:=0;
  FOR i:=1 TO 16 DO
    start[SUCC(i)]:=start[i]+(count[i] SHL (16-i));
  IF start[17]<>0 THEN
    HALT(1);
  jutbits:=16-TableBits;
  FOR i:=1 TO TableBits DO
    BEGIN
      start[i]:=start[i] SHR jutbits;weight[i]:=1 SHL (TableBits-i);
    END;
  i:=SUCC(TableBits);
  WHILE (i<=16) DO BEGIN
    weight[i]:=1 SHL (16-i);INC(i);
  END;
  i:=start[SUCC(TableBits)] SHR jutbits;
  IF i<>0 THEN
    BEGIN
      k:=1 SHL TableBits;
      WHILE i<>k DO BEGIN
        Table^[i]:=0;INC(i);
      END;
    END;
  Avail:=nchar;mask:=1 SHL (15-TableBits);
  FOR ch:=0 TO PRED(nchar) DO
    BEGIN
      Len:=BitLen^[ch];
      IF Len=0 THEN
  

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