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[zpackage] / tomsfastmath / src / numtheory / fp_gcd.c

diff --git a/tomsfastmath/src/numtheory/fp_gcd.c b/tomsfastmath/src/numtheory/fp_gcd.c
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+/* TomsFastMath, a fast ISO C bignum library.
+ * 
+ * This project is meant to fill in where LibTomMath
+ * falls short.  That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ * 
+ * Tom St Denis, tomstdenis@gmail.com
+ */
+#include <tfm_private.h>
+
+/* c = (a, b) */
+void fp_gcd(fp_int *a, fp_int *b, fp_int *c)
+{
+   fp_int u, v, r;
+
+   /* either zero than gcd is the largest */
+   if (fp_iszero (a) == 1 && fp_iszero (b) == 0) {
+     fp_abs (b, c);
+     return;
+   }
+   if (fp_iszero (a) == 0 && fp_iszero (b) == 1) {
+     fp_abs (a, c);
+     return;
+   }
+
+   /* optimized.  At this point if a == 0 then
+    * b must equal zero too
+    */
+   if (fp_iszero (a) == 1) {
+     fp_zero(c);
+     return;
+   }
+
+   /* sort inputs */
+   if (fp_cmp_mag(a, b) != FP_LT) {
+      fp_init_copy(&u, a);
+      fp_init_copy(&v, b);
+   } else {
+      fp_init_copy(&u, b);
+      fp_init_copy(&v, a);
+   }
+ 
+   fp_zero(&r);
+   while (fp_iszero(&v) == FP_NO) {
+      fp_mod(&u, &v, &r);
+      fp_copy(&v, &u);
+      fp_copy(&r, &v);
+   }
+   fp_copy(&u, c);
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */