IsPrime in Tutorials & Snippets

ID:257766
 
Mar 20 2007, 3:52 pm (Edited by moderator on Mar 20 2007, 5:48 pm)
 
//Title: Prime Number Checker
//Credit to: Xx Dark Wizard xX
//Contributed by: Xx Dark Wizard xX

/*
This will check any number and will return 1 if it is a
prime number and 0 otherwise.
*/
proc
  IsPrime(n)
    if(n % 2 == 0 && n != 2) // even number
      return 0
    var/s = sqrt(n) // avoid constant checking since sqrt() is slow
    for(var/i = 3, i <= s, i+=2)
      if(n % i == 0) // it isn't prime
        return 0
    return 1 // its a prime number


///*
//Testing code/sample implementation
mob
  verb
    Check(n as num)
      if(IsPrime(n))
        src << "[n] is a prime number"
      else
        src << "[n] is not a prime number"
//*/
#1 Mar 20 2007, 5:49 pm
Please follow the format, DarkWiz! I've had to go through and change quite a few of yours. If something doesn't conform to the format, it doesn't get protected under the licence and would probably just fall under standard copyright (i.e., undistributable).
#2 Nov 11 2007, 7:18 am
I think Lummox JR posted a more efficient version of this somewhere. I'll search for it.

Edit:
proc/IsPrime(n)
  var/p=3,psq=9
  if(n>2 && !(n%2)) return 0
  while(psq<=n)
    if(!(n%p)) return 0
    psq+=4*p+4; p+=2
  return 1