Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_sqrt.c

@@ -0,0 +1,67 @@
+#include "tommath_private.h"
+#ifdef MP_SQRT_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* this function is less generic than mp_n_root, simpler and faster */
+mp_err mp_sqrt(const mp_int *arg, mp_int *ret)
+{
+   mp_err err;
+   mp_int t1, t2;
+
+   /* must be positive */
+   if (mp_isneg(arg)) {
+      return MP_VAL;
+   }
+
+   /* easy out */
+   if (mp_iszero(arg)) {
+      mp_zero(ret);
+      return MP_OKAY;
+   }
+
+   if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) {
+      return err;
+   }
+
+   if ((err = mp_init(&t2)) != MP_OKAY) {
+      goto LBL_ERR2;
+   }
+
+   /* First approx. (not very bad for large arg) */
+   mp_rshd(&t1, t1.used/2);
+
+   /* t1 > 0  */
+   if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
+      goto LBL_ERR1;
+   }
+   if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
+      goto LBL_ERR1;
+   }
+   if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
+      goto LBL_ERR1;
+   }
+   /* And now t1 > sqrt(arg) */
+   do {
+      if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
+         goto LBL_ERR1;
+      }
+      if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
+         goto LBL_ERR1;
+      }
+      if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
+         goto LBL_ERR1;
+      }
+      /* t1 >= sqrt(arg) >= t2 at this point */
+   } while (mp_cmp_mag(&t1, &t2) == MP_GT);
+
+   mp_exch(&t1, ret);
+
+LBL_ERR1:
+   mp_clear(&t2);
+LBL_ERR2:
+   mp_clear(&t1);
+   return err;
+}
+
+#endif