Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_mul.c

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+#include "tommath_private.h"
+#ifdef BN_MP_MUL_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
+ */
+
+/* high level multiplication (handles sign) */
+int mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
+{
+   int     res, neg;
+   neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
+
+   /* use Toom-Cook? */
+#ifdef BN_MP_TOOM_MUL_C
+   if (MIN(a->used, b->used) >= TOOM_MUL_CUTOFF) {
+      res = mp_toom_mul(a, b, c);
+   } else
+#endif
+#ifdef BN_MP_KARATSUBA_MUL_C
+      /* use Karatsuba? */
+      if (MIN(a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
+         res = mp_karatsuba_mul(a, b, c);
+      } else
+#endif
+      {
+         /* can we use the fast multiplier?
+          *
+          * The fast multiplier can be used if the output will
+          * have less than MP_WARRAY digits and the number of
+          * digits won't affect carry propagation
+          */
+         int     digs = a->used + b->used + 1;
+
+#ifdef BN_FAST_S_MP_MUL_DIGS_C
+         if ((digs < (int)MP_WARRAY) &&
+             (MIN(a->used, b->used) <=
+              (int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
+            res = fast_s_mp_mul_digs(a, b, c, digs);
+         } else
+#endif
+         {
+#ifdef BN_S_MP_MUL_DIGS_C
+            res = s_mp_mul(a, b, c); /* uses s_mp_mul_digs */
+#else
+            res = MP_VAL;
+#endif
+         }
+      }
+   c->sign = (c->used > 0) ? neg : MP_ZPOS;
+   return res;
+}
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */