#include <linux/kernel.h>
  #include <linux/gcd.h>
  #include <linux/module.h>
  
  /* Greatest common divisor */
  unsigned long gcd(unsigned long a, unsigned long b)
  {
  	unsigned long r;
  
  	if (a < b)
  		swap(a, b);
  	while ((r = a % b) != 0) {
  		a = b;
  		b = r;
  	}
  	return b;
  }
  EXPORT_SYMBOL_GPL(gcd);