CODE EXAMPLE FOR C

how to compress a file in c

#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;
}