A pairing function (szudzik) that supports negative numbers

szudzik.js

// src https://codepen.io/sachmata/post/elegant-pairing

szudzik.getindex = function(x, y) {
    var xx = x >= 0 ? x * 2 : x * -2 - 1;
    var yy = y >= 0 ? y * 2 : y * -2 - 1;
    return (xx >= yy) ? (xx * xx + xx + yy) : (yy * yy + xx);
};

szudzik.unpair = function(z) {
    var sqrtz = Math.floor(Math.sqrt(z));
    var sqz = sqrtz * sqrtz;
    var result1 = ((z - sqz) >= sqrtz) ? [sqrtz, z - sqz - sqrtz] : [z - sqz, sqrtz];
    var xx = result1[0] % 2 === 0 ? result1[0] / 2 : (result1[0] + 1) / -2;
    var yy = result1[1] % 2 === 0 ? result1[1] / 2 : (result1[1] + 1) / -2;
    return [xx, yy];
};

Hi, i stumbled over your code while looking for a pairing function that works with negative numbers. After I reimplemented it in python I have noticed, that you have a small bug in the else branch of the following lines:

var xx = result1[0] % 2 === 0 ? result1[0] / 2 : result1[0] / -2 + 1;
var yy = result1[1] % 2 === 0 ? result1[1] / 2 : result1[1] / -2 + 1;

. In the else-branches of your getindex function you multiply x respectively y with -2 and then subtract 1 from the result. Therefore to invert this part of the function you need to first add 1 and then divide with -2.

To correct this you have to change the mentioned lines to something like this:

    var xx = result1[0] % 2 === 0 ? result1[0] / 2 : (result1[0] + 1 ) / -2;
    var yy = result1[1] % 2 === 0 ? result1[1] / 2 : (result1[1] + 1 )/ -2;

Thanks,
Nick

Thank you for the fix, you're right!

Thanks nick and TheGreatRambler!