rust/src/libcore/uint-template/uint.rs

type T = uint;

/**
 * Divide two numbers, return the result, rounded up.
 *
 * # Arguments
 *
 * * x - an integer
 * * y - an integer distinct from 0u
 *
 * # Return value
 *
 * The smallest integer `q` such that `x/y <= q`.
 */
pure fn div_ceil(x: uint, y: uint) -> uint {
    let div = x / y;
    if x % y == 0u { div }
    else { div + 1u }
}

/**
 * Divide two numbers, return the result, rounded to the closest integer.
 *
 * # Arguments
 *
 * * x - an integer
 * * y - an integer distinct from 0u
 *
 * # Return value
 *
 * The integer `q` closest to `x/y`.
 */
pure fn div_round(x: uint, y: uint) -> uint {
    let div = x / y;
    if x % y * 2u  < y { div }
    else { div + 1u }
}

/**
 * Divide two numbers, return the result, rounded down.
 *
 * Note: This is the same function as `div`.
 *
 * # Arguments
 *
 * * x - an integer
 * * y - an integer distinct from 0u
 *
 * # Return value
 *
 * The smallest integer `q` such that `x/y <= q`. This
 * is either `x/y` or `x/y + 1`.
 */
pure fn div_floor(x: uint, y: uint) -> uint { return x / y; }

/// Produce a uint suitable for use in a hash table
pure fn hash(x: &uint) -> uint { *x }

/**
 * Iterate over the range [`lo`..`hi`), or stop when requested
 *
 * # Arguments
 *
 * * lo - The integer at which to start the loop (included)
 * * hi - The integer at which to stop the loop (excluded)
 * * it - A block to execute with each consecutive integer of the range.
 *        Return `true` to continue, `false` to stop.
 *
 * # Return value
 *
 * `true` If execution proceeded correctly, `false` if it was interrupted,
 * that is if `it` returned `false` at any point.
 */
pure fn iterate(lo: uint, hi: uint, it: fn(uint) -> bool) -> bool {
    let mut i = lo;
    while i < hi {
        if (!it(i)) { return false; }
        i += 1u;
    }
    return true;
}

/// Returns the smallest power of 2 greater than or equal to `n`
#[inline(always)]
fn next_power_of_two(n: uint) -> uint {
    let halfbits: uint = sys::size_of::<uint>() * 4u;
    let mut tmp: uint = n - 1u;
    let mut shift: uint = 1u;
    while shift <= halfbits { tmp |= tmp >> shift; shift <<= 1u; }
    return tmp + 1u;
}

#[test]
fn test_next_power_of_two() {
    assert (uint::next_power_of_two(0u) == 0u);
    assert (uint::next_power_of_two(1u) == 1u);
    assert (uint::next_power_of_two(2u) == 2u);
    assert (uint::next_power_of_two(3u) == 4u);
    assert (uint::next_power_of_two(4u) == 4u);
    assert (uint::next_power_of_two(5u) == 8u);
    assert (uint::next_power_of_two(6u) == 8u);
    assert (uint::next_power_of_two(7u) == 8u);
    assert (uint::next_power_of_two(8u) == 8u);
    assert (uint::next_power_of_two(9u) == 16u);
    assert (uint::next_power_of_two(10u) == 16u);
    assert (uint::next_power_of_two(11u) == 16u);
    assert (uint::next_power_of_two(12u) == 16u);
    assert (uint::next_power_of_two(13u) == 16u);
    assert (uint::next_power_of_two(14u) == 16u);
    assert (uint::next_power_of_two(15u) == 16u);
    assert (uint::next_power_of_two(16u) == 16u);
    assert (uint::next_power_of_two(17u) == 32u);
    assert (uint::next_power_of_two(18u) == 32u);
    assert (uint::next_power_of_two(19u) == 32u);
    assert (uint::next_power_of_two(20u) == 32u);
    assert (uint::next_power_of_two(21u) == 32u);
    assert (uint::next_power_of_two(22u) == 32u);
    assert (uint::next_power_of_two(23u) == 32u);
    assert (uint::next_power_of_two(24u) == 32u);
    assert (uint::next_power_of_two(25u) == 32u);
    assert (uint::next_power_of_two(26u) == 32u);
    assert (uint::next_power_of_two(27u) == 32u);
    assert (uint::next_power_of_two(28u) == 32u);
    assert (uint::next_power_of_two(29u) == 32u);
    assert (uint::next_power_of_two(30u) == 32u);
    assert (uint::next_power_of_two(31u) == 32u);
    assert (uint::next_power_of_two(32u) == 32u);
    assert (uint::next_power_of_two(33u) == 64u);
    assert (uint::next_power_of_two(34u) == 64u);
    assert (uint::next_power_of_two(35u) == 64u);
    assert (uint::next_power_of_two(36u) == 64u);
    assert (uint::next_power_of_two(37u) == 64u);
    assert (uint::next_power_of_two(38u) == 64u);
    assert (uint::next_power_of_two(39u) == 64u);
}

#[test]
fn test_overflows() {
    assert (uint::max_value > 0u);
    assert (uint::min_value <= 0u);
    assert (uint::min_value + uint::max_value + 1u == 0u);
}

#[test]
fn test_div() {
    assert(uint::div_floor(3u, 4u) == 0u);
    assert(uint::div_ceil(3u, 4u)  == 1u);
    assert(uint::div_round(3u, 4u) == 1u);
}