From 6d0f7e48898b51076bd4c844855ab9b1da7edd36 Mon Sep 17 00:00:00 2001
From: Florin Chirica <fchirica96@gmail.com>
Date: Tue, 27 Jun 2023 19:43:46 +0300
Subject: [PATCH] Division by 0 catching. (#1)

* Division by 0 catching.

* Use mpz_sgn.
---
 src/bqfc.c         | 4 ++++
 src/proof_common.h | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/src/bqfc.c b/src/bqfc.c
index 7994192d..54fa8d75 100644
--- a/src/bqfc.c
+++ b/src/bqfc.c
@@ -68,6 +68,10 @@ int bqfc_decompr(mpz_t out_a, mpz_t out_b, const mpz_t D, const struct qfb_c *c)
         mpz_set(t, c->t);
     }
 
+    if (mpz_sgn(c->a) == 0) {
+        ret = -1;
+        goto out;
+    }
     mpz_gcdext(tmp, t_inv, NULL, t, c->a);
     if (mpz_cmp_ui(tmp, 1)) {
         ret = -1;
diff --git a/src/proof_common.h b/src/proof_common.h
index a1c7087a..0054e170 100644
--- a/src/proof_common.h
+++ b/src/proof_common.h
@@ -65,6 +65,9 @@ form DeserializeForm(const integer &D, const uint8_t *bytes, size_t size)
 
 integer FastPow(uint64_t a, uint64_t b, integer& c) {
     integer res, a1 = integer(a);
+    if (mpz_sgn(c.impl) == 0) {
+        throw std::runtime_error("Division by 0");
+    }
     mpz_powm_ui(res.impl, a1.impl, b, c.impl);
     return res;
 }