--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_gcd.c	Mon May 31 18:23:46 2004 +0000
@@ -0,0 +1,107 @@
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://math.libtomcrypt.org
+ */
+#include <tommath.h>
+
+/* Greatest Common Divisor using the binary method */
+int mp_gcd (mp_int * a, mp_int * b, mp_int * c)
+{
+  mp_int  u, v;
+  int     k, u_lsb, v_lsb, res;
+
+  /* either zero than gcd is the largest */
+  if (mp_iszero (a) == 1 && mp_iszero (b) == 0) {
+    return mp_abs (b, c);
+  }
+  if (mp_iszero (a) == 0 && mp_iszero (b) == 1) {
+    return mp_abs (a, c);
+  }
+
+  /* optimized.  At this point if a == 0 then
+   * b must equal zero too
+   */
+  if (mp_iszero (a) == 1) {
+    mp_zero(c);
+    return MP_OKAY;
+  }
+
+  /* get copies of a and b we can modify */
+  if ((res = mp_init_copy (&u, a)) != MP_OKAY) {
+    return res;
+  }
+
+  if ((res = mp_init_copy (&v, b)) != MP_OKAY) {
+    goto __U;
+  }
+
+  /* must be positive for the remainder of the algorithm */
+  u.sign = v.sign = MP_ZPOS;
+
+  /* B1.  Find the common power of two for u and v */
+  u_lsb = mp_cnt_lsb(&u);
+  v_lsb = mp_cnt_lsb(&v);
+  k     = MIN(u_lsb, v_lsb);
+
+  if (k > 0) {
+     /* divide the power of two out */
+     if ((res = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) {
+        goto __V;
+     }
+
+     if ((res = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) {
+        goto __V;
+     }
+  }
+
+  /* divide any remaining factors of two out */
+  if (u_lsb != k) {
+     if ((res = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) {
+        goto __V;
+     }
+  }
+
+  if (v_lsb != k) {
+     if ((res = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) {
+        goto __V;
+     }
+  }
+
+  while (mp_iszero(&v) == 0) {
+     /* make sure v is the largest */
+     if (mp_cmp_mag(&u, &v) == MP_GT) {
+        /* swap u and v to make sure v is >= u */
+        mp_exch(&u, &v);
+     }
+     
+     /* subtract smallest from largest */
+     if ((res = s_mp_sub(&v, &u, &v)) != MP_OKAY) {
+        goto __V;
+     }
+     
+     /* Divide out all factors of two */
+     if ((res = mp_div_2d(&v, mp_cnt_lsb(&v), &v, NULL)) != MP_OKAY) {
+        goto __V;
+     } 
+  } 
+
+  /* multiply by 2**k which we divided out at the beginning */
+  if ((res = mp_mul_2d (&u, k, c)) != MP_OKAY) {
+     goto __V;
+  }
+  c->sign = MP_ZPOS;
+  res = MP_OKAY;
+__V:mp_clear (&u);
+__U:mp_clear (&v);
+  return res;
+}