#include <stdint.h>

​

uint32_t lz77_compress (uint8_t *uncompressed_text, uint32_t uncompressed_size, uint8_t *compressed_text)

{

    uint8_t pointer_length, temp_pointer_length;

    uint16_t pointer_pos, temp_pointer_pos, output_pointer;

    uint32_t compressed_pointer, output_size, coding_pos, output_lookahead_ref, look_behind, look_ahead;

    *((uint32_t *) compressed_text) = uncompressed_size;

    compressed_pointer = output_size = 4;

    for(coding_pos = 0; coding_pos < uncompressed_size; ++coding_pos)

    {

        pointer_pos = 0;

        pointer_length = 0;

        for(temp_pointer_pos = 1; (temp_pointer_pos < 4096) && (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 == 15)

                    break;

            if(temp_pointer_length > pointer_length)

            {

                pointer_pos = temp_pointer_pos;

                pointer_length = temp_pointer_length;

                if(pointer_length == 15)

                    break;

            }

        }

        coding_pos += pointer_length;

        if(pointer_length && (coding_pos == uncompressed_size))

        {

            output_pointer = (pointer_pos << 4) | (pointer_length - 1);

            output_lookahead_ref = coding_pos - 1;

        }

        else

        {

            output_pointer = (pointer_pos << 4) | pointer_length;

            output_lookahead_ref = coding_pos;

        }

        *((uint32_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;

    uint16_t input_pointer, pointer_pos;

    uint32_t compressed_pointer, coding_pos, pointer_offset, uncompressed_size;

    uncompressed_size = *((uint32_t *) compressed_text);

    compressed_pointer = 4;

    for(coding_pos = 0; coding_pos < uncompressed_size; ++coding_pos)

    {

        input_pointer = *((uint32_t *) (compressed_text + compressed_pointer));

        compressed_pointer += 2;

        pointer_pos = input_pointer >> 4;

        pointer_length = input_pointer & 15;

        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;

}

​