capacity.nct

//! Shared checked arithmetic and geometric storage growth.

see ./index.nct

const maximum_usize: usize = 18446744073709551615

func checked_add(left: usize, right: usize): usize? {
    if right > maximum_usize - left {
        return none
    }
    return left + right
}

func checked_multiply(left: usize, right: usize): usize? {
    if left == 0 || right == 0 {
        return 0
    }
    if left > maximum_usize / right {
        return none
    }
    return left * right
}

func growth_capacity(current: usize, required: usize): usize {
    if required <= current {
        return current
    }
    let doubled: usize = checked_add(current, current) otherwise {
        return maximum_usize
    }
    if doubled < required {
        return required
    }
    return doubled
}