Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_mul_2d.c

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+#include "tommath_private.h"
+#ifdef BN_MP_MUL_2D_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 by a certain bit count */
+int mp_mul_2d(const mp_int *a, int b, mp_int *c)
+{
+   mp_digit d;
+   int      res;
+
+   /* copy */
+   if (a != c) {
+      if ((res = mp_copy(a, c)) != MP_OKAY) {
+         return res;
+      }
+   }
+
+   if (c->alloc < (c->used + (b / DIGIT_BIT) + 1)) {
+      if ((res = mp_grow(c, c->used + (b / DIGIT_BIT) + 1)) != MP_OKAY) {
+         return res;
+      }
+   }
+
+   /* shift by as many digits in the bit count */
+   if (b >= DIGIT_BIT) {
+      if ((res = mp_lshd(c, b / DIGIT_BIT)) != MP_OKAY) {
+         return res;
+      }
+   }
+
+   /* shift any bit count < DIGIT_BIT */
+   d = (mp_digit)(b % DIGIT_BIT);
+   if (d != 0u) {
+      mp_digit *tmpc, shift, mask, r, rr;
+      int x;
+
+      /* bitmask for carries */
+      mask = ((mp_digit)1 << d) - (mp_digit)1;
+
+      /* shift for msbs */
+      shift = (mp_digit)DIGIT_BIT - d;
+
+      /* alias */
+      tmpc = c->dp;
+
+      /* carry */
+      r    = 0;
+      for (x = 0; x < c->used; x++) {
+         /* get the higher bits of the current word */
+         rr = (*tmpc >> shift) & mask;
+
+         /* shift the current word and OR in the carry */
+         *tmpc = ((*tmpc << d) | r) & MP_MASK;
+         ++tmpc;
+
+         /* set the carry to the carry bits of the current word */
+         r = rr;
+      }
+
+      /* set final carry */
+      if (r != 0u) {
+         c->dp[(c->used)++] = r;
+      }
+   }
+   mp_clamp(c);
+   return MP_OKAY;
+}
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */