数据压缩 -- 源码

(******************************************************************************)
(* *)
(* LH5.PAS *)
(* *)
(* This code compress/decompress data using the same algorithm as LHArc 2.x *)
(* It is roughly derived from the C source code of AR002 (a C version of a *)
(* subset of LHArc, written by Haruhiko Okomura). *)
(* The algorithm was created by Haruhiko Okomura and Haruyasu Yoshizaki. *)
(* *)
(* 6/11/98 Modified by Gregory L. Bullock with the hope of fixing a
problem when compiled for 32-bits.
Some variables of type TWord are sometimes treated as
ARRAY[0..32759]OF Integer; and other times as
ARRAY[0..32759]OF Word;
InsertNode, for example, expects a signed integer since it
includes the expression Position^[t]<0.
To account for this, I''''ve defined TwoByteInt which is a 2-byte
signed integer on either platform.
*)

(* 4/20/98 Modified by Gregory L. Bullock (bullock@tsppd.com) *)
(* - to use TStream (and descendents) instead of files, *)
(* - to reduce the memory requirements in the data segment, *)
(* - to changed the program to a unit. *)
(* The interface consists of the two procedures *)
(* procedure LHACompress(InStr, OutStr: TStream); *)
(* procedure LHAExpand(InStr, OutStr: TStream); *)
(* These procedures DO NOT change the current position of EITHER *)
(* TStream before performing their function. Thus, LHACompress *)
(* starts compressing at InStr''''s current position and continues to *)
(* the end of InStr, placing the compressed output in OutStr *)
(* starting at OutStr''''s current position. If you need the entirety *)
(* of InStr compressed or uncompressed, you''''ll need to set *)
(* InStr.Position := 0 before calling one of these procedures. *)
(* *)
(* See the test program at the end of this unit for an example of *)
(* how to use these procedures. *)
(* *)
(* Changing this to a unit required the (internal) addition of *)
(* procedure FreeMemory; *)
(* procedure InitMemory; *)
(* to ensure that memory gets initialized properly between calls *)
(* to the unit''''s interface procedures. *)
(******************************************************************************)

Unit Lh5Unit;

{Turn off range checking - MANDATORY ! and stack checking (to speed up things)}
{$B-,R-,S-}

{$DEFINE PERCOLATE}
(*
NOTE :
LHArc uses a "percolating" update of its Lempel-Ziv structures.
If you use the percolating method, the compressor will run slightly faster,
using a little more memory, and will be slightly less efficient than the
standard method.
You can choose either method, and note that the decompressor is not
affected by this choice and is able to decompress data created by each one
of the compressors.
*)

interface

uses
SysUtils, Classes;

procedure LHACompress(InStr, OutStr: TStream);
(* LHACompress starts compressing at InStr''''s current position and continues
to the end of InStr, placing the compressed output in OutStr starting at
OutStr''''s current position. If you need the entirety of InStr compressed
you''''ll need to set InStr.Position := 0 before calling.
*)
procedure LHAExpand(InStr, OutStr: TStream);
(* LHAExpand starts expanding at InStr''''s current position and continues to
the end of InStr, placing the expanded output in OutStr starting at
OutStr''''s current position. If you need the entirety of InStr expanded
you''''ll need to set InStr.Position := 0 before calling.