Have a bound on the CM walkdown, the discriminant grows too much otherwise.

2 files changed, 16 insertions, 8 deletions

diff --git a/src/cm/cm_any.c b/src/cm/cm_any.c
index 368ce77..cd319ab 100644
--- a/src/cm/cm_any.c
+++ b/src/cm/cm_any.c
@@ -353,15 +353,9 @@ GENERATOR(cm_gen_curve_unique) {
 	const char *order_s = (const char *)args->args;
 	GEN order = strtoi(order_s);
 	GEN e;
-	if (min_d && min_roots && min_curve == curve &&
-	    min_roots->used < min_roots->total) {
-		debug_log("Reusing roots.");
-		// We can just use the roots we have stored and take some out.
-		e = cm_construct_curve(order, min_d->d, min_d->p, min_roots, false);
-	} else if (min_d && min_curve == curve) {
+	if (min_d && min_curve == curve) {
 		debug_log("Reusing min D = %Pi", min_d->d);
-		// We just have the discriminant but no roots (or they are used up), we
-		// need to continue
+		// We have some discriminant, cannot use the roots because the D with walkdown was too large.
 		if (min_d->d && isclone(min_d->d)) {
 			gunclone(min_d->d);
 		}
@@ -421,9 +415,17 @@ GENERATOR(cm_gen_curve_unique) {
 			GEN power = gel(powers, i);
 			debug_log("Walking down with %Pi %Pi", prime, power);
 			GEN exp = mulis(power, 2);
+			debug_log("%Pi, %Pi", prime, exp);
 			GEN mul = powii(prime, exp);
+			debug_log("%Pi", mul);
 			d = mulii(d, mul);
+			debug_log("d %Pi", d);
 		}
+		if (logint(d, gen_2) > 64) {
+            fprintf(err, "Discriminant too large.");
+            avma = ltop;
+            return -3;
+        }
 		if (min_d->d && isclone(min_d->d)) {
 			gunclone(min_d->d);
 		}
diff --git a/src/math/subgroup.c b/src/math/subgroup.c
index fdf45a5..0b5c515 100644
--- a/src/math/subgroup.c
+++ b/src/math/subgroup.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2017-2018 J08nY
  */
 #include "subgroup.h"
+#include "io/output.h"
 
 /**
  * @brief All prime divisors of a given integer with multiplicity.
@@ -46,6 +47,11 @@ static GEN subgroups_2n_factors(GEN factors, size_t min_bits) {
 	long nprimes = glength(factors);
 	if (nprimes == min_bits) return NULL;
 	GEN amount = int2n(nprimes);
+	long abits = logint(amount, gen_2);
+	if (abits >= 64) {
+		fprintf(err, "Too many factors to generate points (%li bits).", abits);
+		return NULL;
+	}
 	GEN groups = gtovec0(gen_0, itos(amount) - (min_bits * nprimes) - 1);
 
 	size_t i = 0;