const std = @import("std");

// rounds up a u12 to the nearest factor of 4 and returns the difference
// (padding)
pub fn roundUp4Padding(comptime T: type, n: T) T {
    return roundUp4(T, n) - n;
}

// rounds up a u12 to the nearest factor of 4.
pub fn roundUp4(comptime T: type, n: T) T {
    return ((n + 3) & ~@as(T, 3));
}

const testing = std.testing;

test "padding" {
    try testing.expectEqual(roundUp4Padding(u12, 0), 0);
    try testing.expectEqual(roundUp4Padding(u12, 1), 3);
    try testing.expectEqual(roundUp4Padding(u12, 2), 2);
    try testing.expectEqual(roundUp4Padding(u12, 3), 1);
    try testing.expectEqual(roundUp4Padding(u12, 4), 0);
    try testing.expectEqual(roundUp4Padding(u12, 40), 0);
    try testing.expectEqual(roundUp4Padding(u12, 41), 3);
    try testing.expectEqual(roundUp4Padding(u12, 42), 2);
    try testing.expectEqual(roundUp4Padding(u12, 43), 1);
    try testing.expectEqual(roundUp4Padding(u12, 44), 0);
    try testing.expectEqual(roundUp4Padding(u12, 4091), 1);
    try testing.expectEqual(roundUp4Padding(u12, 4092), 0);
}