Initial Mangos Three Commit

dep/tomlib/Math/src/bn_mp_div_d.c

@@ -0,0 +1,99 @@
+#include "tommath_private.h"
+#ifdef BN_MP_DIV_D_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+static int s_is_power_of_two(mp_digit b, int *p)
+{
+   int x;
+
+   /* fast return if no power of two */
+   if ((b == 0u) || ((b & (b-1u)) != 0u)) {
+      return 0;
+   }
+
+   for (x = 0; x < MP_DIGIT_BIT; x++) {
+      if (b == ((mp_digit)1<<(mp_digit)x)) {
+         *p = x;
+         return 1;
+      }
+   }
+   return 0;
+}
+
+/* single digit division (based on routine from MPI) */
+int mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
+{
+   mp_int  q;
+   mp_word w;
+   mp_digit t;
+   int     res, ix;
+
+   /* cannot divide by zero */
+   if (b == 0u) {
+      return MP_VAL;
+   }
+
+   /* quick outs */
+   if ((b == 1u) || MP_IS_ZERO(a)) {
+      if (d != NULL) {
+         *d = 0;
+      }
+      if (c != NULL) {
+         return mp_copy(a, c);
+      }
+      return MP_OKAY;
+   }
+
+   /* power of two ? */
+   if (s_is_power_of_two(b, &ix) == 1) {
+      if (d != NULL) {
+         *d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
+      }
+      if (c != NULL) {
+         return mp_div_2d(a, ix, c, NULL);
+      }
+      return MP_OKAY;
+   }
+
+#ifdef BN_MP_DIV_3_C
+   /* three? */
+   if (b == 3u) {
+      return mp_div_3(a, c, d);
+   }
+#endif
+
+   /* no easy answer [c'est la vie].  Just division */
+   if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
+      return res;
+   }
+
+   q.used = a->used;
+   q.sign = a->sign;
+   w = 0;
+   for (ix = a->used - 1; ix >= 0; ix--) {
+      w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
+
+      if (w >= b) {
+         t = (mp_digit)(w / b);
+         w -= (mp_word)t * (mp_word)b;
+      } else {
+         t = 0;
+      }
+      q.dp[ix] = t;
+   }
+
+   if (d != NULL) {
+      *d = (mp_digit)w;
+   }
+
+   if (c != NULL) {
+      mp_clamp(&q);
+      mp_exch(&q, c);
+   }
+   mp_clear(&q);
+
+   return res;
+}
+
+#endif