Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_lshd.c

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+#include "tommath_private.h"
+#ifdef BN_MP_LSHD_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
+ */
+
+/* shift left a certain amount of digits */
+int mp_lshd(mp_int *a, int b)
+{
+   int     x, res;
+
+   /* if its less than zero return */
+   if (b <= 0) {
+      return MP_OKAY;
+   }
+   /* no need to shift 0 around */
+   if (mp_iszero(a) == MP_YES) {
+      return MP_OKAY;
+   }
+
+   /* grow to fit the new digits */
+   if (a->alloc < (a->used + b)) {
+      if ((res = mp_grow(a, a->used + b)) != MP_OKAY) {
+         return res;
+      }
+   }
+
+   {
+      mp_digit *top, *bottom;
+
+      /* increment the used by the shift amount then copy upwards */
+      a->used += b;
+
+      /* top */
+      top = a->dp + a->used - 1;
+
+      /* base */
+      bottom = (a->dp + a->used - 1) - b;
+
+      /* much like mp_rshd this is implemented using a sliding window
+       * except the window goes the otherway around.  Copying from
+       * the bottom to the top.  see bn_mp_rshd.c for more info.
+       */
+      for (x = a->used - 1; x >= b; x--) {
+         *top-- = *bottom--;
+      }
+
+      /* zero the lower digits */
+      top = a->dp;
+      for (x = 0; x < b; x++) {
+         *top++ = 0;
+      }
+   }
+   return MP_OKAY;
+}
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */