From 6187e06d92adfe093d47791b9028ebf45c8afa75 Mon Sep 17 00:00:00 2001
From: J08nY
Date: Sat, 30 Sep 2017 17:42:37 +0200
Subject: Fixed generation with cofactor bound.

Might be slow, but should work. Needs to factor curve order.
I wonder if I should store the factored curve order somewhere.
---
 src/gen/order.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

(limited to 'src/gen/order.c')

diff --git a/src/gen/order.c b/src/gen/order.c
index 2e20294..1ad7a93 100644
--- a/src/gen/order.c
+++ b/src/gen/order.c
@@ -48,21 +48,36 @@ GENERATOR(order_gen_smallfact) {
 	pari_ulong smallfact = *(pari_ulong *)args->args;
 	pari_sp ltop = avma;
 	GEN fact = mpfact(smallfact);
+	pari_ulong lfact = 0;
 	if (lgefint(fact) > 3) {
-		smallfact = 0;
+		lfact = 0;
 	} else {
-		smallfact = itou(fact);
+		lfact = itou(fact);
 	}
 
-	GEN order = ellsea(curve->curve, smallfact);
-	if (gequal0(order) || gequal1(gcdii(order, fact))) {
+	GEN order = ellsea(curve->curve, lfact);
+	if (gequal0(order)) {
 		avma = ltop;
 		return -4;
-	} else {
-		curve->order = order;
-		obj_insert_shallow(curve->curve, 1, curve->order);
-		return 1;
 	}
+
+	GEN factors = factor(order);
+	GEN primes = gel(factors, 1);
+	GEN powers = gel(factors, 2);
+	long len = glength(primes);
+	GEN total = gen_1;
+	for (long i = 1; i < len; ++i) {
+		GEN pow = powii(gel(primes, i), gel(powers, i));
+		total = mulii(total, pow);
+		if (abscmpiu(total, smallfact) > 0) {
+			avma = ltop;
+			return -4;
+		}
+	}
+
+	curve->order = gerepileupto(ltop, order);
+	obj_insert_shallow(curve->curve, 1, curve->order);
+	return 1;
 }
 
 GENERATOR(order_gen_prime) {
-- 
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