176 lines
12 KiB
C
Executable File
176 lines
12 KiB
C
Executable File
/******************************************************************************/
|
|
/* */
|
|
/* COMPRESS.H */
|
|
/* */
|
|
/******************************************************************************/
|
|
/* */
|
|
/* Author : Ross Williams. */
|
|
/* Date : December 1989. */
|
|
/* */
|
|
/* This header file defines the interface to a set of functions called */
|
|
/* 'compress', each member of which implements a particular data compression */
|
|
/* algorithm. */
|
|
/* */
|
|
/* Normally in C programming, for each .H file, there is a corresponding .C */
|
|
/* file that implements the functions promised in the .H file. */
|
|
/* Here, there are many .C files corresponding to this header file. */
|
|
/* Each comforming implementation file contains a single function */
|
|
/* called 'compress' that implements a single data compression */
|
|
/* algorithm that conforms with the interface specified in this header file. */
|
|
/* Only one algorithm can be linked in at a time in this organization. */
|
|
/* */
|
|
/******************************************************************************/
|
|
/* */
|
|
/* DEFINITION OF FUNCTION COMPRESS */
|
|
/* =============================== */
|
|
/* */
|
|
/* Summary of Function Compress */
|
|
/* ---------------------------- */
|
|
/* The action that 'compress' takes depends on its first argument called */
|
|
/* 'action'. The function provides three actions: */
|
|
/* */
|
|
/* - Return information about the algorithm. */
|
|
/* - Compress a block of memory. */
|
|
/* - Decompress a block of memory. */
|
|
/* */
|
|
/* Parameters */
|
|
/* ---------- */
|
|
/* See the formal C definition later for a description of the parameters. */
|
|
/* */
|
|
/* Constants */
|
|
/* --------- */
|
|
/* COMPRESS_OVERRUN: The constant COMPRESS_OVERRUN defines by how many bytes */
|
|
/* an algorithm is allowed to expand a block during a compression operation. */
|
|
/* */
|
|
/* Although compression algorithms usually compress data, there will always */
|
|
/* be data that a given compressor will expand (this can be proven). */
|
|
/* Fortunately, the degree of expansion can be limited to a single bit, by */
|
|
/* copying over the input data if the data gets bigger during compression. */
|
|
/* To allow for this possibility, the first bit of a compressed */
|
|
/* representation can be used as a flag indicating whether the */
|
|
/* input data was copied over, or truly compressed. In practice, the first */
|
|
/* byte would be used to store this bit so as to maintain byte alignment. */
|
|
/* */
|
|
/* Unfortunately, in general, the only way to tell if an algorithm will */
|
|
/* expand a particular block of data is to run the algorithm on the data. */
|
|
/* If the algorithm does not continuously monitor how many output bytes it */
|
|
/* has written, it might write an output block far larger than the input */
|
|
/* block before realizing that it has done so. */
|
|
/* On the other hand, continuous checks on output length are inefficient. */
|
|
/* */
|
|
/* To cater for all these problems, this interface definition: */
|
|
/* > Allows a compression algorithm to return an output block that is up to */
|
|
/* COMPRESS_OVERRUN bytes longer than the input block. */
|
|
/* > Allows a compression algorithm to write up to COMPRESS_OVERRUN bytes */
|
|
/* more than the length of the input block to the memory of the output */
|
|
/* block regardless of the length of the output block eventually returned. */
|
|
/* This allows an algorithm to overrun the length of the input block in the */
|
|
/* output block by up to COMPRESS_OVERRUN bytes between expansion checks. */
|
|
/* */
|
|
/* The problem does not arise for decompression. */
|
|
/* */
|
|
/* Identity Action */
|
|
/* --------------- */
|
|
/* > action must be COMPRESS_ACTION_IDENTITY. */
|
|
/* > p_dst_len must point to a longword to receive a longword address. */
|
|
/* > The value of the other parameters does not matter. */
|
|
/* > After execution, the longword that p_dst_len points to will be a pointer */
|
|
/* to a structure of type compress_identity. */
|
|
/* Thus, for example, after the call, (*p_dst_len)->memory will return the */
|
|
/* number of bytes of working memory that the algorithm requires to run. */
|
|
/* > The values of the identity structure returned are fixed constant */
|
|
/* attributes of the algorithm and must not vary from call to call. */
|
|
/* */
|
|
/* Common Requirements for Compression and Decompression Actions */
|
|
/* ------------------------------------------------------------- */
|
|
/* > wrk_mem must point to an unused block of memory of a length specified in */
|
|
/* the algorithm's identity block. The identity block can be obtained by */
|
|
/* making a separate call to compress, specifying the identity action. */
|
|
/* > The INPUT BLOCK is defined to be Memory[src_addr,src_addr+src_len-1]. */
|
|
/* > dst_len will be used to denote *p_dst_len. */
|
|
/* > dst_len is not read by compress, only written. */
|
|
/* > The value of dst_len is defined only upon termination. */
|
|
/* > The OUTPUT BLOCK is defined to be Memory[dst_addr,dst_addr+dst_len-1]. */
|
|
/* */
|
|
/* Compression Action */
|
|
/* ------------------ */
|
|
/* > action must be COMPRESS_ACTION_COMPRESS. */
|
|
/* > src_len must be in the range [0,COMPRESS_MAX_ORG]. */
|
|
/* > The OUTPUT ZONE is defined to be */
|
|
/* Memory[dst_addr,dst_addr+src_len-1+COMPRESS_OVERRUN]. */
|
|
/* > The function can modify any part of the output zone regardless of the */
|
|
/* final length of the output block. */
|
|
/* > The input block and the output zone must not overlap. */
|
|
/* > dst_len will be in the range [0,src_len+COMPRESS_OVERRUN]. */
|
|
/* > dst_len will be in the range [0,COMPRESS_MAX_COM] (from prev fact). */
|
|
/* > The output block will consist of a representation of the input block. */
|
|
/* */
|
|
/* Decompression Action */
|
|
/* -------------------- */
|
|
/* > action must be COMPRESS_ACTION_DECOMPRESS. */
|
|
/* > The input block must be the result of an earlier compression operation. */
|
|
/* > If the previous fact is true, the following facts must also be true: */
|
|
/* > src_len will be in the range [0,COMPRESS_MAX_COM]. */
|
|
/* > dst_len will be in the range [0,COMPRESS_MAX_ORG]. */
|
|
/* > The input and output blocks must not overlap. */
|
|
/* > Only the output block is modified. */
|
|
/* > Upon termination, the output block will consist of the bytes contained */
|
|
/* in the input block passed to the earlier compression operation. */
|
|
/* */
|
|
/******************************************************************************/
|
|
|
|
#include "port.h"
|
|
|
|
#define COMPRESS_ACTION_IDENTITY 0
|
|
#define COMPRESS_ACTION_COMPRESS 1
|
|
#define COMPRESS_ACTION_DECOMPRESS 2
|
|
|
|
#define COMPRESS_OVERRUN 1024
|
|
#define COMPRESS_MAX_COM 0x70000000
|
|
#define COMPRESS_MAX_ORG (COMPRESS_MAX_COM-COMPRESS_OVERRUN)
|
|
|
|
#define COMPRESS_MAX_STRLEN 255
|
|
//#ifndef __MWERKS__
|
|
extern "C"{
|
|
//#endif
|
|
/* The following structure provides information about the algorithm. */
|
|
/* > The top bit of id must be zero. The remaining bits must be chosen by */
|
|
/* the author of the algorithm by tossing a coin 31 times. */
|
|
/* > The amount of memory requested by the algorithm is specified in bytes */
|
|
/* and must be in the range [0,0x70000000]. */
|
|
/* > All strings s must be such that strlen(s)<=COMPRESS_MAX_STRLEN. */
|
|
typedef struct
|
|
{
|
|
ULONG id; /* Identifying number of algorithm. */
|
|
ULONG memory; /* Number of bytes of working memory required. */
|
|
|
|
char *name; /* Name of algorithm. */
|
|
char *version; /* Version number. */
|
|
char *date; /* Date of release of this version. */
|
|
char *copyright; /* Copyright message. */
|
|
|
|
char *author; /* Author of algorithm. */
|
|
char *affiliation; /* Affiliation of author. */
|
|
char *vendor; /* Where the algorithm can be obtained. */
|
|
}compress_identity;
|
|
|
|
int xcompress( /* Single function interface to compression algorithm. */
|
|
UWORD action, /* Action to be performed. */
|
|
UBYTE *wrk_mem, /* Working memory temporarily given to routine to use. */
|
|
UBYTE *src_adr, /* Address of input data. */
|
|
ULONG src_len, /* Length of input data. */
|
|
ULONG dst_max, /* Allocated length of output buffer. */
|
|
UBYTE *dst_adr, /* Address of output data. */
|
|
ULONG *p_dst_len /* Pointer to a longword where routine will write: */
|
|
/* If action=..IDENTITY => Adr of id structure. */
|
|
/* If action=..COMPRESS => Length of output data. */
|
|
/* If action=..DECOMPRESS => Length of output data. */
|
|
);
|
|
//#ifndef __MWERKS__
|
|
}
|
|
//#endif
|
|
/******************************************************************************/
|
|
/* End of COMPRESS.H */
|
|
/******************************************************************************/
|
|
|