function react_str_replace(string $units, ?string $exclude = null): int
{
    if($exclude)
    {
        $units = str_replace(array($exclude, strtoupper($exclude)), '', $units);
    }

    $len = strlen($units);
    $i = 0;

    while($i<$len-1)
    {
        $diff = ord($units[$i]) - ord($units[$i+1]);

        if((($diff ^ ($diff >> 31)) - ($diff >> 31)) === 32)
        {
            $units = substr($units, 0, $i) . substr($units, $i+2);
            if($i) $i--;
            $len -= 2;
        } else {
            $i++;
        }
    }

    return $len;
}