Greatest Common Devisor implementation from the Linux source code

gcd.c

#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);