Ecstatica 2 RAW decompression

struct TwoNibbles
{
    signed char low : 4;
    signed char high : 4;
};


void decode_image_data(unsigned char *input_ptr, unsigned char *output_ptr)
{
    unsigned char cur_val = 0;

    while(1)
    {
        unsigned char span_header = *input_ptr++;
        unsigned char span_type = span_header & 3;
        unsigned char span_len = span_header >> 2;

        if(span_len == 0)
            break;

        switch(span_type)
        {
            case 0:         // Packed delta encoding
                do
                {
                    TwoNibbles *two_nibbles_ptr = (TwoNibbles*)input_ptr++;

                    cur_val += two_nibbles_ptr->low;
                    *output_ptr++ = cur_val;
                    span_len --;

                    if(span_len == 0)
                        break;

                    cur_val += two_nibbles_ptr->high;
                    *output_ptr++ = cur_val;
                    span_len --;
                }
                while(span_len);
                break;

            case 1:         // Fill
            case 3:
                {
                    cur_val = *input_ptr++;

                    do
                    {
                        *output_ptr++ = cur_val;
                        span_len --;
                    }
                    while(span_len);
                }
                break;

            case 2:         // Copy
                do
                {
                    cur_val = *input_ptr++;
                    *output_ptr++ = cur_val;
                    span_len --;
                }
                while(span_len);
                break;
        }
    }
}


void decode_depth_data(unsigned char *input_ptr, unsigned short int *output_ptr)
{
    unsigned short int cur_val = 0;

    while(1)
    {
        unsigned char span_header = *input_ptr++;
        unsigned char span_type = span_header & 3;
        unsigned char span_len = span_header >> 2;

        if(span_len == 0)
            break;

        switch(span_type)
        {
            case 0:         // Packed delta encoding
                do
                {
                    TwoNibbles *two_nibbles_ptr = (TwoNibbles*)input_ptr++;

                    cur_val += two_nibbles_ptr->low << 2;
                    *output_ptr++ = cur_val;
                    span_len--;

                    if(span_len == 0)
                        break;

                    cur_val += two_nibbles_ptr->high << 2;
                    *output_ptr++ = cur_val;
                    span_len--;
                }
                while(span_len);
                break;

            case 1:         // Delta encoding
                do
                {
                    cur_val += (*(signed char*)input_ptr++) << 2;
                    *output_ptr++ = cur_val;
                    span_len --;
                }
                while(span_len);
                break;

            case 2:         // Copy
                do
                {
                    cur_val = *(unsigned short int*)input_ptr << 2;
                    input_ptr += 2;
                    *output_ptr++ = cur_val;
                    span_len --;
                }
                while(span_len);
                break;

            case 3:         // Fill
                {
                    cur_val = *(unsigned short int*)input_ptr << 2;
                    input_ptr += 2;
                    do
                    {
                        *output_ptr++ = cur_val;
                        span_len --;
                    }
                    while(span_len);
                }
                break;
        }
    }
}