From 8c927a1764e4a985179f9f93d266ee3b84d21422 Mon Sep 17 00:00:00 2001
From: Paul Zimmermann <Paul.Zimmermann@inria.fr>
Date: Wed, 26 Jun 2024 09:49:16 +0200
Subject: [PATCH] fixed https://gitlab.inria.fr/zimmerma/ecm/-/issues/21876
---
parametrizations.c | 10 +++++++---
test.ecm | 3 +++
2 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/parametrizations.c b/parametrizations.c
index 7b15e8c5..44249024 100644
--- a/parametrizations.c
+++ b/parametrizations.c
@@ -425,11 +425,15 @@ int
get_curve_from_random_parameter (mpz_t f, mpres_t A, mpres_t x, mpz_t sigma,
int param, mpmod_t modulus, gmp_randstate_t rng)
{
- int ret;
+ int ret = ECM_ERROR;
/* initialize the random number generator if not already done */
init_randstate (rng);
- do
+ /* we perform only a fixed number of tries to find a suitable curve,
+ to avoid an infinite loop in corner cases (for example with -param 1,
+ there is no valid sigma for n=3, see
+ https://gitlab.inria.fr/zimmerma/ecm/-/issues/21876) */
+ for (int i = 0; ret == ECM_ERROR && i < 10; i++)
{
if (param == ECM_PARAM_SUYAMA)
{
@@ -453,7 +457,7 @@ get_curve_from_random_parameter (mpz_t f, mpres_t A, mpres_t x, mpz_t sigma,
}
else
return ECM_ERROR;
- } while (ret == ECM_ERROR);
+ }
return ret;
}
diff --git a/test.ecm b/test.ecm
index eff5ab57..07c1e9b4 100755
--- a/test.ecm
+++ b/test.ecm
@@ -534,6 +534,9 @@ checkcode $? 0
echo 18446744073709551557 | $ECM -param 1 -A 312656731337392125 11000
checkcode $? 8
+# non-regression test for https://gitlab.inria.fr/zimmerma/ecm/-/issues/21876
+echo 3 | $ECM -param 1 1000 1000; checkcode $? 1
+
# test -bsaves/-bloads
TEST=test.ecm.s$$
echo 18446744073709551557 | $ECM -param 1 -A 1 -bsaves $TEST 11000
--
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