round_half_to_even.sf

#!/usr/bin/ruby

func round_nth(orig, nth) {

    var n = orig.abs
    var p = 10**nth;

    n *= p;
    n += 0.5;
    n -= 0.5 if n.is_odd;

    n = n.int;
    n /= p;
    n = -n if (orig < 0);

    return n;
}

var tests = [

    # original | rounded | places
    [+1.6,      +2,        0],
    [+1.5,      +2,        0],
    [+1.4,      +1,        0],
    [+0.6,      +1,        0],
    [+0.5,      0,         0],
    [+0.4,      0,         0],
    [-0.4,      0,         0],
    [-0.5,      0,         0],
    [-0.6,      -1,        0],
    [-1.4,      -1,        0],
    [-1.5,      -2,        0],
    [-1.6,      -2,        0],
    [3.016,     3.02,      2],
    [3.013,     3.01,      2],
    [3.015,     3.02,      2],
    [3.045,     3.04,      2],
    [3.04501,   3.05,      2],
    [-1234.555, -1000,     -3],
    [-1234.555, -1200,     -2],
    [-1234.555, -1230,     -1],
    [-1234.555, -1235,     0],
    [-1234.555, -1234.6,   1],
    [-1234.555, -1234.56,  2],
    [-1234.555, -1234.555, 3],
];

tests.each { |t|
    var (n, expected, places) = t...
    var rounded = round_nth(n, places);

    print "#{n} rounded to #{places} digits is ";

    if (rounded == expected) {
        say rounded;
    }
    else {
        die "#{expected}, but got #{rounded}! This is wrong!";
    }
}