c# - Largest Prime Factor algorithm optimization -

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i'm trying improve interesting algorithm as can.

for now, have this:

using system;  class program {      static void main()     {         ulong num, largest_pfact;         uint = 2;         string strnum;          console.write("enter number: ");         strnum = console.readline();         num = ulong.parse(strnum);         largest_pfact = num;           while (i < math.sqrt((double) largest_pfact))         {             if (i % 2 != 0 | == 2) {                 if (largest_pfact % == 0)                      largest_pfact /= i;             }              i++;         }          console.writeline("largest prime factor of {0} is: {1}", num, largest_pfact);         console.readline();      } }

so ideas?

thanks!

edit: implemented ben's algorithm, eveyone help!

i've got faster algorithm here.

it eliminates square root , handles repeated factors correctly.

optimizing further:

static private ulong maxfactor (ulong n) {     unchecked     {         while (n > 3 && 0 == (n & 1)) n >>= 1;          uint k = 3;         ulong k2 = 9;         ulong delta = 16;         while (k2 <= n)         {             if (n % k == 0)             {                 n /= k;             }             else             {                 k += 2;                 if (k2 + delta < delta) return n;                 k2 += delta;                 delta += 8;             }         }     }      return n; }

here's working demo: http://ideone.com/sicil


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