derp.h

function int unusedTID(int start, int end)
{
    if (end <= 0)
    {
        end = 0x7FFFFFFF;
    }
    int ret;

    for (ret = start; ret < end; ret++)
    {
        if (ThingCount(0, ret) == 0)
        {
            return ret;
            break;
        }
    }

    return -1;
}