Modular multiplicative inverse - Swift implementation

modInverse.swift

/*
given a and m, function finds x for a * x = 1 (mod m)

24 * x = 1 (mod 5)
24 = x*exp(-1) (mod 5)
x = 4

modInverse(a: 24, m: 5) returns optional(4)
*/

func modInverse(a: Int, m: Int) -> Int? {
	let tmp = a % m
    for i in 1..<m {
      if (tmp * i % m == 1) {
        return i;
      }
    }
  return nil    
}