Import code from previous AssetBuilder version

thirdparty/libtommath/bn_mp_sub_d.c

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+#include "tommath_private.h"
+#ifdef BN_MP_SUB_D_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
+ */
+
+/* single digit subtraction */
+int mp_sub_d(const mp_int *a, mp_digit b, mp_int *c)
+{
+   mp_digit *tmpa, *tmpc, mu;
+   int       res, ix, oldused;
+
+   /* grow c as required */
+   if (c->alloc < (a->used + 1)) {
+      if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) {
+         return res;
+      }
+   }
+
+   /* if a is negative just do an unsigned
+    * addition [with fudged signs]
+    */
+   if (a->sign == MP_NEG) {
+      mp_int a_ = *a;
+      a_.sign = MP_ZPOS;
+      res     = mp_add_d(&a_, b, c);
+      c->sign = MP_NEG;
+
+      /* clamp */
+      mp_clamp(c);
+
+      return res;
+   }
+
+   /* setup regs */
+   oldused = c->used;
+   tmpa    = a->dp;
+   tmpc    = c->dp;
+
+   /* if a <= b simply fix the single digit */
+   if (((a->used == 1) && (a->dp[0] <= b)) || (a->used == 0)) {
+      if (a->used == 1) {
+         *tmpc++ = b - *tmpa;
+      } else {
+         *tmpc++ = b;
+      }
+      ix      = 1;
+
+      /* negative/1digit */
+      c->sign = MP_NEG;
+      c->used = 1;
+   } else {
+      /* positive/size */
+      c->sign = MP_ZPOS;
+      c->used = a->used;
+
+      /* subtract first digit */
+      *tmpc    = *tmpa++ - b;
+      mu       = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u);
+      *tmpc++ &= MP_MASK;
+
+      /* handle rest of the digits */
+      for (ix = 1; ix < a->used; ix++) {
+         *tmpc    = *tmpa++ - mu;
+         mu       = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u);
+         *tmpc++ &= MP_MASK;
+      }
+   }
+
+   /* zero excess digits */
+   while (ix++ < oldused) {
+      *tmpc++ = 0;
+   }
+   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 */