[fsbl] add fsbl for cv181x/cv180x

Change-Id: I6809bc5016d4bc148f62be2ed3f8e928ec111f19

fsbl/lib/libtommath/bn_mp_dr_is_modulus.c

@@ -0,0 +1,40 @@
+#include "tommath_private.h"
+#ifdef BN_MP_DR_IS_MODULUS_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.
+ *
+ * SPDX-License-Identifier: Unlicense
+ */
+
+/* determines if a number is a valid DR modulus */
+int mp_dr_is_modulus(const mp_int *a)
+{
+   int ix;
+
+   /* must be at least two digits */
+   if (a->used < 2) {
+      return 0;
+   }
+
+   /* must be of the form b**k - a [a <= b] so all
+    * but the first digit must be equal to -1 (mod b).
+    */
+   for (ix = 1; ix < a->used; ix++) {
+      if (a->dp[ix] != MP_MASK) {
+         return 0;
+      }
+   }
+   return 1;
+}
+
+#endif
+
+/* ref:         $Format:%D$ */
+/* git commit:  $Format:%H$ */
+/* commit time: $Format:%ai$ */