gfx_lzw.c

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/* tiny LZW codec
 * Based on code by Mark Nelson, Dr. Dobb's Journal October, 1989
 */

#include "fb_gfx.h"
#include "fb_gfx_lzw.h"

LZW_ENTRY fb_lzw_entry[TABLE_SIZE];

static unsigned char *decode_string(unsigned char *buffer, int code)
{
        int index = 0;

        while (code > 255) {
                *buffer++ = fb_lzw_entry[code].value;
                code = fb_lzw_entry[code].prefix;
                if (index++ >= MAX_CODE - 1)
                        return NULL;
        }
        *buffer = code;
        return buffer;
}

FBCALL int fb_hDecode
        (
                const unsigned char *in_buffer,
                ssize_t in_size,
                unsigned char *out_buffer,
                ssize_t *out_size
        )
{
        unsigned short new_code, old_code, next_code = 256;
        unsigned char *limit, decode_stack[MAX_CODE], *string, byte, bit = 0;

        INPUT_CODE(old_code);
        byte = old_code;
        *out_buffer++ = old_code;
        limit = out_buffer + *out_size;
        *out_size = 1;
        while (in_size > 0) {
                INPUT_CODE(new_code);
                if (new_code == MAX_CODE)
                        return 0;
                if (new_code >= next_code) {
                        *decode_stack = byte;
                        string = decode_string(decode_stack + 1, old_code);
                }
                else
                        string = decode_string(decode_stack, new_code);
                if (!string)
                        return -1;
                byte = *string;
                while (string >= decode_stack) {
                        if (out_buffer >= limit)
                                return -1;
                        *out_buffer++ = *string--;
                        (*out_size)++;
                }
                if (next_code < MAX_CODE) {
                        fb_lzw_entry[next_code].prefix = old_code;
                        fb_lzw_entry[next_code].value = byte;
                        next_code++;
                }
                old_code = new_code;
        }
        return -1;
}