1 files changed, 78 insertions, 0 deletions
diff --git a/bn_mp_exteuclid.c b/bn_mp_exteuclid.c
new file mode 100644
index 0000000..c4ebab4
--- /dev/null
+++ b/bn_mp_exteuclid.c
@@ -0,0 +1,78 @@
+#include <tommath.h>
+#ifdef BN_MP_EXTEUCLID_C
+/* 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, tomstdenis@iahu.ca, http://math.libtomcrypt.org
+ */
+
+/* Extended euclidean algorithm of (a, b) produces 
+   a*u1 + b*u2 = u3
+ */
+int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
+{
+   mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp;
+   int err;
+
+   if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
+      return err;
+   }
+
+   /* initialize, (u1,u2,u3) = (1,0,a) */
+   mp_set(&u1, 1);
+   if ((err = mp_copy(a, &u3)) != MP_OKAY)                                        { goto _ERR; }
+
+   /* initialize, (v1,v2,v3) = (0,1,b) */
+   mp_set(&v2, 1);
+   if ((err = mp_copy(b, &v3)) != MP_OKAY)                                        { goto _ERR; }
+
+   /* loop while v3 != 0 */
+   while (mp_iszero(&v3) == MP_NO) {
+       /* q = u3/v3 */
+       if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY)                         { goto _ERR; }
+
+       /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
+       if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
+       if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY)                             { goto _ERR; }
+       if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
+       if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY)                             { goto _ERR; }
+       if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY)                              { goto _ERR; }
+       if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY)                             { goto _ERR; }
+
+       /* (u1,u2,u3) = (v1,v2,v3) */
+       if ((err = mp_copy(&v1, &u1)) != MP_OKAY)                                  { goto _ERR; }
+       if ((err = mp_copy(&v2, &u2)) != MP_OKAY)                                  { goto _ERR; }
+       if ((err = mp_copy(&v3, &u3)) != MP_OKAY)                                  { goto _ERR; }
+
+       /* (v1,v2,v3) = (t1,t2,t3) */
+       if ((err = mp_copy(&t1, &v1)) != MP_OKAY)                                  { goto _ERR; }
+       if ((err = mp_copy(&t2, &v2)) != MP_OKAY)                                  { goto _ERR; }
+       if ((err = mp_copy(&t3, &v3)) != MP_OKAY)                                  { goto _ERR; }
+   }
+
+   /* make sure U3 >= 0 */
+   if (u3.sign == MP_NEG) {
+      mp_neg(&u1, &u1);
+      mp_neg(&u2, &u2);
+      mp_neg(&u3, &u3);
+   }
+
+   /* copy result out */
+   if (U1 != NULL) { mp_exch(U1, &u1); }
+   if (U2 != NULL) { mp_exch(U2, &u2); }
+   if (U3 != NULL) { mp_exch(U3, &u3); }
+
+   err = MP_OKAY;
+_ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
+   return err;
+}
+#endif