PHP Cantor implementation using BCMath extension

cantor.php

<?php
# Need Composer with PHPUnit
require 'vendor/autoload.php';

function cantor($x, $y)
{
    // ((x + y) * (x + y + 1)) / 2 + y;
    return bcadd(bcdiv(bcmul(bcadd($x, $y), bcadd(bcadd($x, $y), 1)), 2), $y);
}

function uncantor($z)
{
    $pair = [];
    $t = bcdiv(bcadd(-1, bcsqrt( bcadd(1, bcmul(8, $z)) )), 2);
    $pair[0] = bcsub(bcdiv(bcmul($t, bcadd($t, 3)), 2), $z);
    $pair[1] = bcsub($z, bcdiv(bcmul($t, bcadd($t, 1)), 2));
    return $pair;
}

$x = '1234';
$y = '6789';
$z = cantor($x, $y);
list($xx, $yy) = uncantor($z);

\PHPUnit_Framework_Assert::assertEquals($x, $xx);
\PHPUnit_Framework_Assert::assertEquals($y, $yy);

echo "$x\n";
echo "$y\n";
echo "$z\n";

echo "$xx\n";
echo "$yy\n";

More info: http://sachiniscool.blogspot.com/2011/06/cantor-pairing-function-and-reversal.html