I change salt but it not working #1

function encode_str($str) {
    $encoded    = '';
    **$alpha_map = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'];**
    $str        = ''.$str;
    $len        = strlen($str);
    $ascii_arr  = [];
    **$salt       = 1505;//rand(100, (999 - 255));**
    echo $salt;
    
    for ($x = 0; $x < $len; $x++) {
        $ascii_arr[$x] = (rand(1, 9) * 1000) + ($salt + ord($str[$x]));
    }
    
    $enc        = implode('', $ascii_arr) . $salt;
    $enc_len    = strlen($enc);
    
    for ($x = 0; $x < $enc_len; $x++) {
        if (array_key_exists($enc[$x], $alpha_map)) {
            $encoded .= $alpha_map[$enc[$x]];
        } else {
            $encoded .= $enc[$x];
        }
    }
    
    return strtolower($encoded);
}
function decode_str($str) {
    $str = strtoupper($str);
    $unit_size = 4;
    $alphatonum = function($s) {
        $alpha_map = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'];
        $l = strlen($s);
        $s_ = '';
        for ($x = 0; $x < $l; $x++) {
            $pos = array_search($s[$x], $alpha_map);
            $s_ .= in_array($s[$x], $alpha_map) ? array_search($s[$x], $alpha_map) : $s[$x];
        }
        return $s_;
    };
    
    $decoded    = '';
    **$salt       = $alphatonum(substr($str, -4));     
    $data       = $alphatonum(substr($str, 0, strlen($str) - 4));**
    
    $loop       = strlen($data) / $unit_size;
    $unit_arr   = [];
    for ($x = 0; $x < $loop; $x++) {
        $unit = substr($data, $x * $unit_size, $unit_size);
        
        **$ascii_ = ($unit % 10000) - $salt;**
        $decoded .= chr($ascii_);
    }
    
    return $decoded;
}