Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/s_mp_log.c

@@ -0,0 +1,81 @@
+#include "tommath_private.h"
+#ifdef S_MP_LOG_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+mp_err s_mp_log(const mp_int *a, mp_digit base, int *c)
+{
+   mp_err err;
+   int high, low;
+   mp_int bracket_low, bracket_high, bracket_mid, t, bi_base;
+
+   mp_ord cmp = mp_cmp_d(a, base);
+   if ((cmp == MP_LT) || (cmp == MP_EQ)) {
+      *c = cmp == MP_EQ;
+      return MP_OKAY;
+   }
+
+   if ((err =
+           mp_init_multi(&bracket_low, &bracket_high,
+                         &bracket_mid, &t, &bi_base, NULL)) != MP_OKAY) {
+      return err;
+   }
+
+   low = 0;
+   mp_set(&bracket_low, 1uL);
+   high = 1;
+
+   mp_set(&bracket_high, base);
+
+   /*
+       A kind of Giant-step/baby-step algorithm.
+       Idea shamelessly stolen from https://programmingpraxis.com/2010/05/07/integer-logarithms/2/
+       The effect is asymptotic, hence needs benchmarks to test if the Giant-step should be skipped
+       for small n.
+    */
+   while (mp_cmp(&bracket_high, a) == MP_LT) {
+      low = high;
+      if ((err = mp_copy(&bracket_high, &bracket_low)) != MP_OKAY) {
+         goto LBL_END;
+      }
+      high <<= 1;
+      if ((err = mp_sqr(&bracket_high, &bracket_high)) != MP_OKAY) {
+         goto LBL_END;
+      }
+   }
+   mp_set(&bi_base, base);
+
+   while ((high - low) > 1) {
+      int mid = (high + low) >> 1;
+
+      if ((err = mp_expt_n(&bi_base, mid - low, &t)) != MP_OKAY) {
+         goto LBL_END;
+      }
+      if ((err = mp_mul(&bracket_low, &t, &bracket_mid)) != MP_OKAY) {
+         goto LBL_END;
+      }
+      cmp = mp_cmp(a, &bracket_mid);
+      if (cmp == MP_LT) {
+         high = mid;
+         mp_exch(&bracket_mid, &bracket_high);
+      }
+      if (cmp == MP_GT) {
+         low = mid;
+         mp_exch(&bracket_mid, &bracket_low);
+      }
+      if (cmp == MP_EQ) {
+         *c = mid;
+         goto LBL_END;
+      }
+   }
+
+   *c = (mp_cmp(&bracket_high, a) == MP_EQ) ? high : low;
+
+LBL_END:
+   mp_clear_multi(&bracket_low, &bracket_high, &bracket_mid,
+                  &t, &bi_base, NULL);
+   return err;
+}
+
+
+#endif