Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_clamp.c

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+#include "tommath_private.h"
+#ifdef BN_MP_CLAMP_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
+ */
+
+/* trim unused digits
+ *
+ * This is used to ensure that leading zero digits are
+ * trimed and the leading "used" digit will be non-zero
+ * Typically very fast.  Also fixes the sign if there
+ * are no more leading digits
+ */
+void mp_clamp(mp_int *a)
+{
+   /* decrease used while the most significant digit is
+    * zero.
+    */
+   while ((a->used > 0) && (a->dp[a->used - 1] == 0u)) {
+      --(a->used);
+   }
+
+   /* reset the sign flag if used == 0 */
+   if (a->used == 0) {
+      a->sign = MP_ZPOS;
+   }
+}
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */