c++ - Basic Algorithm Optimization -

my current assignment create basic algorithm finds magic number (which 1). magic number can found either dividing number 2 until it's magic, or multiplying odd number 3, adding 1, dividing 2 until 1. must each positive integer 3 until 5 billion.

magic = 1;

div = 2;

start = 3;

max = 5000000000;

bool isodd(int x); void ismagic(int x);  int main () {    clock_t starttime = clock();   cout << "beginning loop" << endl;    (int = start; < max; i++)    {      if ( isodd(i) == false )        ismagic(i);     else if ( isodd(i) == true )       ismagic(i);     }    clock_t finishtime = clock();   cout << "looping took " << double(finishtime - starttime) / clocks_per_sec << " seconds" << endl;    return 0; }   bool isodd(int x) {    if( x % div == 0 )     return false;   else     return true;  }  void ismagic(int x) {    if( isodd(x) == false ) //is   {      while( x > magic )     {         x /= div;     };    }   else if( isodd(x) == true ) //is odd   {      while( x > magic )     {        x *= start;       x += magic;       x /= div;      };    }    return; } 

this works, however, rather slow. -o3 flag in makefile takes around 115 seconds complete task. professor stated decent time ~60 seconds. how able optimize this?

i think misunderstood assignment. "either dividing number 2 until it's magic, or multiplying odd number 3 , adding 1" should implemeneted as

while( x > 1 ) {   if( iseven(x) )   {     x /= 2;   }   else   {     x *= 3;     x += 1;   } } 

assuming validity of collatz conjecture, can further optimized as

x = 1;