PHP: Have a 1/2 chance to add or subtract 1 ..?

[Plague]

I could be wrong but I think the issue is here:

// $numnew = new number
// $curnum = current number
// $max = upper limit (5 in this case)

if (rand(1,2) == 1) {
$numnew = ($curnum + rand(-1,1));
}

if ($numnew == 0) {
$numnew = $max;
}

if ($numnew > $max) {
$numnew = 1;
}

I think maybe setting it like this:

if (rand(0,4) == 1) {

That might rectify the issue.