A prime sieve

Author: czurnieden

bn_mp_next_small_prime.c

@@ -0,0 +1,35 @@
+#include "tommath_private.h"
+#ifdef BN_MP_NEXT_SMALL_PRIME_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/*
+ * Mimics behaviour of Pari/GP's nextprime(n)
+ * If n is prime set *result to n else set *result to first prime > n
+ * and 0 in case of error
+ */
+mp_err mp_next_small_prime(mp_sieve_prime n, mp_sieve_prime *result, mp_sieve *sieve)
+{
+   mp_sieve_prime ret = 0;
+   int e = MP_OKAY;
+
+   if (n < 2) {
+      *result = 2;
+      return e;
+   }
+
+   for (; ret == 0 && n != 0; n++) {
+      if (n > MP_SIEVE_BIGGEST_PRIME) {
+         return MP_SIEVE_MAX_REACHED;
+      }
+      /* just call mp_is_small_prime(), it does all of the heavy work */
+      if ((e = mp_is_small_prime(n, &ret, sieve)) != MP_OKAY) {
+         *result = 0;
+         return e;
+      }
+   }
+   *result = n - 1;
+   return e;
+}
+#endif
+

bn_mp_prec_small_prime.c

@@ -0,0 +1,37 @@
+#include "tommath_private.h"
+#ifdef BN_MP_PREC_SMALL_PRIME_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/*
+ * Mimics behaviour of Pari/GP's precprime(n)
+ * If n is prime set *result to n else set *result to first prime < n
+ * and 0 in case of error
+ */
+mp_err mp_prec_small_prime(mp_sieve_prime n, mp_sieve_prime *result, mp_sieve *sieve)
+{
+   mp_sieve_prime ret = 0;
+   int e = MP_OKAY;
+
+   if (n == 2) {
+      *result = 2;
+      return e;
+   }
+
+   if (n < 2) {
+      *result = 0;
+      return e;
+   }
+
+   for (; ret == 0; n--) {
+      if ((e = mp_is_small_prime(n, &ret, sieve)) != MP_OKAY) {
+         *result = 0;
+         return e;
+      }
+   }
+   *result = n + 1;
+
+   return e;
+}
+#endif
+