Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_2expt.c

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+#include "tommath_private.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.
+ *
+ * SPDX-License-Identifier: Unlicense
+ */
+
+/* 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 << (mp_digit)(b % DIGIT_BIT);
+
+   return MP_OKAY;
+}
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */