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+#include <tommath.h>
+#ifdef BN_MP_2EXPT_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@gmail.com, http://math.libtomcrypt.com
+ */
+
+/* computes a = 2**b
+ *
+ * Simple algorithm which zeroes the int, grows it then just sets one bit
+ * as required.
+ */
+int
+mp_2expt (mp_int * a, int b)
+{
+ int res;
+
+ /* zero a as per default */
+ mp_zero (a);
+
+ /* grow a to accomodate the single bit */
+ if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
+ return res;
+ }
+
+ /* set the used count of where the bit will go */
+ a->used = b / DIGIT_BIT + 1;
+
+ /* put the single bit in its place */
+ a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
+
+ return MP_OKAY;
+}
+#endif