Generate defined ranges of keys to generate unqiue array list

getkeyrange.php

/*
* e.g. A=1 - B=2 - Z=26 - AA=27 - CZ=104 - DA=105 - ZZ=702 - AAA=703
*/
function stringtointvalue($str)
{
	$amount = 0;
	$strarra = array_reverse(str_split($str));

	for ($i = 0; $i < strlen($str); $i++) {
		$amount += (ord($strarra[$i]) - 64) * pow(26, $i);
	}
	return $amount;
}
function positionalcomparison($a, $b)
{
	$a1 = stringtointvalue($a);
	$b1 = stringtointvalue($b);
	if ($a1 > $b1) return 1;
	else if ($a1 < $b1) return -1;
	else return 0;
}

function getcolumnrange($min, $max)
{
	$pointer = strtolower($min);
	$output = array();
	while (positionalcomparison($pointer, strtolower($max)) <= 0) {
		array_push($output, $pointer);
		$pointer++;
	}
	return $output;
}
  
  getcolumnrange('a', 'zzz'); // limit  ~18000