ช่วยเขียนโค้ดอันนี้ให้หน่อยครับ ผมทำไม่เป็นจริงๆ ถ้าทำไม่ได้จริงๆ อาจารย์จะให้ติด "ไอ"

<?php
// list all primes between 2 and some integer 
// using the Sieve of Erastothenes
function listPrimes($end) {
  // generate an array of all possible integers
  // between the first prime and the supplied limit
  $sieve = range(2, $end);

  // retrieve the size of the array
  $size = sizeof($sieve);
  // reset internal array pointer to beginning of array
  reset($sieve);

  // iterate over the array
  while (list($key, $val) = each($sieve)) {
    // for each element
    // check if subsequent elements are divisible by it
    // remove them from the array if so
    for ($x=$key+1; $x<$size; $x++) {
      if ($sieve[$x] % $val == 0) {
        unset($sieve[$x]);
      }
    }
  }
  // at the end, elements left in array are primes
  return $sieve;
}

// list all the primes between 2 and 100
// result: "2 3 5 7...83 89 97"
echo implode(" ", listPrimes(100));
?>