lzssd.c File Reference

#include <system.h>
#include <lzss.h>

Go to the source code of this file.

Macros
#define	ENSURE_BYTES
#define	WRITE_BYTE

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

ENSURE_BYTES

#define ENSURE_BYTES

Value:

    do {                               \
    if (i_ptr >= i_end) {                               \
        read = system->read(input, &inbuf[0],           \
                            input_buffer_size);         \
        if (read <= 0) {                                \
            system->free(window);                       \
            return (read < 0) ? MSPACK_ERR_READ         \
                              : MSPACK_ERR_OK;          \
        }                                               \
        i_ptr = &inbuf[0]; i_end = &inbuf[read];        \
    }                                                   \
} while (0)

Definition at line 17 of file lzssd.c.

WRITE_BYTE

#define WRITE_BYTE

Value:

    do {                                 \
    if (system->write(output, &window[pos], 1) != 1) {  \
        system->free(window);                           \
        return MSPACK_ERR_WRITE;                        \
    }                                                   \
} while (0)

Definition at line 30 of file lzssd.c.

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().