lz.c

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <math.h>

uint32_t lz77_compress (uint8_t *uncompressed_text, uint32_t uncompressed_size, uint8_t *compressed_text, uint8_t pointer_length_width)
{
    uint16_t pointer_pos, temp_pointer_pos, output_pointer, pointer_length, temp_pointer_length;
    uint32_t compressed_pointer, output_size, coding_pos, output_lookahead_ref, look_behind, look_ahead;
    uint16_t pointer_pos_max, pointer_length_max;
    pointer_pos_max = pow(2, 16 - pointer_length_width);
    pointer_length_max = pow(2, pointer_length_width);

    *((uint32_t *) compressed_text) = uncompressed_size;
    *(compressed_text + 4) = pointer_length_width;
    compressed_pointer = output_size = 5;
    
    for(coding_pos = 0; coding_pos < uncompressed_size; ++coding_pos)
    {
        pointer_pos = 0;
        pointer_length = 0;
        for(temp_pointer_pos = 1; (temp_pointer_pos < pointer_pos_max) && (temp_pointer_pos <= coding_pos); ++temp_pointer_pos)
        {
            look_behind = coding_pos - temp_pointer_pos;
            look_ahead = coding_pos;
            for(temp_pointer_length = 0; uncompressed_text[look_ahead++] == uncompressed_text[look_behind++]; ++temp_pointer_length)
                if(temp_pointer_length == pointer_length_max)
                    break;
            if(temp_pointer_length > pointer_length)
            {
                pointer_pos = temp_pointer_pos;
                pointer_length = temp_pointer_length;
                if(pointer_length == pointer_length_max)
                    break;
            }
        }
        coding_pos += pointer_length;
        if((coding_pos == uncompressed_size) && pointer_length)
        {
            output_pointer = (pointer_length == 1) ? 0 : ((pointer_pos << pointer_length_width) | (pointer_length - 2));
            output_lookahead_ref = coding_pos - 1;
        }
        else
        {
            output_pointer = (pointer_pos << pointer_length_width) | (pointer_length ? (pointer_length - 1) : 0);
            output_lookahead_ref = coding_pos;
        }
        *((uint16_t *) (compressed_text + compressed_pointer)) = output_pointer;
        compressed_pointer += 2;
        *(compressed_text + compressed_pointer++) = *(uncompressed_text + output_lookahead_ref);
        output_size += 3;
    }

    return output_size;
}

uint32_t lz77_decompress (uint8_t *compressed_text, uint8_t *uncompressed_text)
{
    uint8_t pointer_length_width;
    uint16_t input_pointer, pointer_length, pointer_pos, pointer_length_mask;
    uint32_t compressed_pointer, coding_pos, pointer_offset, uncompressed_size;

    uncompressed_size = *((uint32_t *) compressed_text);
    pointer_length_width = *(compressed_text + 4);
    compressed_pointer = 5;

    pointer_length_mask = pow(2, pointer_length_width) - 1;

    for(coding_pos = 0; coding_pos < uncompressed_size; ++coding_pos)
    {
        input_pointer = *((uint16_t *) (compressed_text + compressed_pointer));
        compressed_pointer += 2;
        pointer_pos = input_pointer >> pointer_length_width;
        pointer_length = pointer_pos ? ((input_pointer & pointer_length_mask) + 1) : 0;
        if(pointer_pos)
            for(pointer_offset = coding_pos - pointer_pos; pointer_length > 0; --pointer_length)
                uncompressed_text[coding_pos++] = uncompressed_text[pointer_offset++];
        *(uncompressed_text + coding_pos) = *(compressed_text + compressed_pointer++);
    }

    return coding_pos;
}

long fsize (FILE *in)
{
    long pos, length;
    pos = ftell(in);
    fseek(in, 0L, SEEK_END);
    length = ftell(in);
    fseek(in, pos, SEEK_SET);
    return length;
}

uint32_t file_lz77_compress (char *filename_in, char *filename_out, size_t malloc_size, uint8_t pointer_length_width)
{
    FILE *in, *out;
    uint8_t *uncompressed_text, *compressed_text;
    uint32_t uncompressed_size, compressed_size;

    in = fopen(filename_in, "r");
    if(in == NULL)
        return 0;
    uncompressed_size = fsize(in);
    uncompressed_text = malloc(uncompressed_size);
    if((uncompressed_size != fread(uncompressed_text, 1, uncompressed_size, in)))
        return 0;
    fclose(in);

    compressed_text = malloc(malloc_size);

    compressed_size = lz77_compress(uncompressed_text, uncompressed_size, compressed_text, pointer_length_width);

    out = fopen(filename_out, "w");
    if(out == NULL)
        return 0;
    if((compressed_size != fwrite(compressed_text, 1, compressed_size, out)))
        return 0;
    fclose(out);

    return compressed_size;
}

uint32_t file_lz77_decompress (char *filename_in, char *filename_out)
{
    FILE *in, *out;
    uint32_t compressed_size, uncompressed_size;
    uint8_t *compressed_text, *uncompressed_text;

    in = fopen(filename_in, "r");
    if(in == NULL)
        return 0;
    compressed_size = fsize(in);
    compressed_text = malloc(compressed_size);
    if(fread(compressed_text, 1, compressed_size, in) != compressed_size)
        return 0;
    fclose(in);

    uncompressed_size = *((uint32_t *) compressed_text);
    uncompressed_text = malloc(uncompressed_size);

    if(lz77_decompress(compressed_text, uncompressed_text) != uncompressed_size)
        return 0;

    out = fopen(filename_out, "w");
    if(out == NULL)
        return 0;
    if(fwrite(uncompressed_text, 1, uncompressed_size, out) != uncompressed_size)
        return 0;
    fclose(out);

    return uncompressed_size;
}

int main (int argc, char const *argv[])
{
    FILE *in;
    in = fopen("./lz.c", "r");
    if(in == NULL)
        return 0;
    printf("Original size: %ld\n", fsize(in));
    fclose(in);
    for(uint8_t i = 1; i < 16; ++i)
        printf("Compressed (%i): %u, decompressed: (%u)\n", i, file_lz77_compress("./lz.c", "lz.c.z77", 10000000, i), file_lz77_decompress("./lz.c.z77", "lz-2.c"));
    return 0;
}