Roland LP sample decoding

stream_sample_t rolandpcm_device::decode_sample(int8_t data)
{
    int16_t val;
    int16_t sign;
    uint8_t shift;
    stream_sample_t result;

    if (data < 0)
    {
        sign = -1;
        val = -data;
    }
    else
    {
        sign = +1;
        val = data;
    }

    // thanks to Sarayan for figuring out the decoding formula
    shift = val >> 4;
    val &= 0x0F;
    if (! shift)
        result = val;
    else
        result = (0x10 + val) << (shift - 1);
    return result * sign;
}