lzss.h File Reference

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Macros
#define	LZSS_WINDOW_SIZE   (4096)
#define	LZSS_WINDOW_FILL   (0x20)
#define	LZSS_MODE_EXPAND   (0)
#define	LZSS_MODE_MSHELP   (1)
#define	LZSS_MODE_QBASIC   (2)

Functions
int	lzss_decompress (struct mspack_system *system, struct mspack_file *input, struct mspack_file *output, int input_buffer_size, int mode)

Macro Definition Documentation

LZSS_MODE_EXPAND

#define LZSS_MODE_EXPAND   (0)

Definition at line 22 of file lzss.h.

LZSS_MODE_MSHELP

#define LZSS_MODE_MSHELP   (1)

Definition at line 23 of file lzss.h.

LZSS_MODE_QBASIC

#define LZSS_MODE_QBASIC   (2)

Definition at line 24 of file lzss.h.

LZSS_WINDOW_FILL

#define LZSS_WINDOW_FILL   (0x20)

Definition at line 20 of file lzss.h.

LZSS_WINDOW_SIZE

#define LZSS_WINDOW_SIZE   (4096)

Definition at line 19 of file lzss.h.

Function Documentation

lzss_decompress()

int lzss_decompress	(	struct mspack_system *	system,
		struct mspack_file *	input,
		struct mspack_file *	output,
		int	input_buffer_size,
		int	mode
	)

Decompresses an LZSS stream.

Input bytes will be read in as necessary using the system->read() function with the input file handle given. This will continue until system->read() returns 0 bytes, or an error. Errors will be passed out of the function as MSPACK_ERR_READ errors. Input streams should convey an "end of input stream" by refusing to supply all the bytes that LZSS asks for when they reach the end of the stream, rather than return an error code.

Output bytes will be passed to the system->write() function, using the output file handle given. More than one call may be made to system->write().

As EXPAND.EXE (SZDD/KWAJ), Microsoft Help and QBasic have slightly different encodings for the control byte and matches, a "mode" parameter is allowed, to choose the encoding.

Parameters

system	an mspack_system structure used to read from the input stream and write to the output stream, also to allocate and free memory.
input	an input stream with the LZSS data.
output	an output stream to write the decoded data to.
input_buffer_size	the number of bytes to use as an input bitstream buffer.
mode	one of LZSS_MODE_EXPAND, LZSS_MODE_MSHELP or LZSS_MODE_QBASIC

Returns

an error code, or MSPACK_ERR_OK if successful

Definition at line 37 of file lzssd.c.

{
    unsigned char *window, *inbuf, *i_ptr, *i_end;
    unsigned int pos, i, c, invert, mpos, len;
    int read;
 
    /* check parameters */
    if (!system || input_buffer_size < 1 || (mode != LZSS_MODE_EXPAND &&
        mode != LZSS_MODE_MSHELP && mode != LZSS_MODE_QBASIC))
    {
        return MSPACK_ERR_ARGS;
    }
 
    /* allocate memory */
    window = (unsigned char *) system->alloc(system, LZSS_WINDOW_SIZE + input_buffer_size);
    if (!window) return MSPACK_ERR_NOMEMORY;
 
    /* initialise decompression */
    inbuf = &window[LZSS_WINDOW_SIZE];
    memset(window, LZSS_WINDOW_FILL, (size_t) LZSS_WINDOW_SIZE);
    pos = LZSS_WINDOW_SIZE - ((mode == LZSS_MODE_QBASIC) ? 18 : 16);
    invert = (mode == LZSS_MODE_MSHELP) ? ~0 : 0;
    i_ptr = i_end = &inbuf[0];
 
    /* loop forever; exit condition is in ENSURE_BYTES macro */
    for (;;) {
        ENSURE_BYTES; c = *i_ptr++ ^ invert;
        for (i = 0x01; i & 0xFF; i <<= 1) {
            if (c & i) {
                /* literal */
                ENSURE_BYTES; window[pos] = *i_ptr++;
                WRITE_BYTE;
                pos++; pos &= LZSS_WINDOW_SIZE - 1;
            }
            else {
                /* match */
                ENSURE_BYTES; mpos = *i_ptr++;
                ENSURE_BYTES; mpos |= (*i_ptr & 0xF0) << 4;
                len = (*i_ptr++ & 0x0F) + 3;
                while (len--) {
                    window[pos] = window[mpos];
                    WRITE_BYTE;
                    pos++;  pos  &= LZSS_WINDOW_SIZE - 1;
                    mpos++; mpos &= LZSS_WINDOW_SIZE - 1;
                }
            }
        }
    }
 
    /* not reached */
    system->free(window);
    return MSPACK_ERR_OK;
}

References mspack_system::alloc, c, ENSURE_BYTES, mspack_system::free, i, inbuf, invert(), len, LZSS_MODE_EXPAND, LZSS_MODE_MSHELP, LZSS_MODE_QBASIC, LZSS_WINDOW_FILL, LZSS_WINDOW_SIZE, memset(), MSPACK_ERR_ARGS, MSPACK_ERR_NOMEMORY, MSPACK_ERR_OK, pos, read(), and WRITE_BYTE.

Referenced by kwajd_extract(), and szddd_extract().