#include <linux/kernel.h>
  #include <linux/gcd.h>
  #include <linux/export.h>
  
  /*
   * This implements the binary GCD algorithm. (Often attributed to Stein,
   * but as Knuth has noted, appears in a first-century Chinese math text.)
   *
   * This is faster than the division-based algorithm even on x86, which
   * has decent hardware division.
   */
  
  #if !defined(CONFIG_CPU_NO_EFFICIENT_FFS) && !defined(CPU_NO_EFFICIENT_FFS)
  
  /* If __ffs is available, the even/odd algorithm benchmarks slower. */
  unsigned long gcd(unsigned long a, unsigned long b)
  {
  	unsigned long r = a | b;
  
  	if (!a || !b)
  		return r;
  
  	b >>= __ffs(b);
  	if (b == 1)
  		return r & -r;
  
  	for (;;) {
  		a >>= __ffs(a);
  		if (a == 1)
  			return r & -r;
  		if (a == b)
  			return a << __ffs(r);
  
  		if (a < b)
  			swap(a, b);
  		a -= b;
  	}
  }
  
  #else
  
  /* If normalization is done by loops, the even/odd algorithm is a win. */
  unsigned long gcd(unsigned long a, unsigned long b)
  {
  	unsigned long r = a | b;
  
  	if (!a || !b)
  		return r;
  
  	/* Isolate lsbit of r */
  	r &= -r;
  
  	while (!(b & r))
  		b >>= 1;
  	if (b == r)
  		return r;
  
  	for (;;) {
  		while (!(a & r))
  			a >>= 1;
  		if (a == r)
  			return r;
  		if (a == b)
  			return a;
  
  		if (a < b)
  			swap(a, b);
  		a -= b;
  		a >>= 1;
  		if (a & r)
  			a += b;
  		a >>= 1;
  	}
  }
  
  #endif
  
  EXPORT_SYMBOL_GPL(gcd);