From a829b87b00ba8fda4c9d810b2e680a6dc5184526 Mon Sep 17 00:00:00 2001
From: Steffen Jaeckel <s@jaeckel.eu>
Date: Sat, 22 Sep 2018 16:36:56 +0200
Subject: [PATCH 1/2] add testcase of #118

---
 demo/demo.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/demo/demo.c b/demo/demo.c
index ff67fcc..b5af727 100644
--- a/demo/demo.c
+++ b/demo/demo.c
@@ -382,6 +382,37 @@ int main(void)
       }
    }
 
+   // mp_invmod corner-case of https://github.com/libtom/libtommath/issues/118
+   printf("\n\nTesting: mp_invmod");
+   {
+      const char *a_ = "47182BB8DF0FFE9F61B1F269BACC066B48BA145D35137D426328DC3F88A5EA44";
+      const char *b_ = "FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFF";
+      const char *should_ = "0521A82E10376F8E4FDEF9A32A427AC2A0FFF686E00290D39E3E4B5522409596";
+
+      if (mp_read_radix(&a, a_, 16) != MP_OKAY) {
+         printf("\nmp_read_radix(a) failed!");
+         return EXIT_FAILURE;
+      }
+      if (mp_read_radix(&b, b_, 16) != MP_OKAY) {
+         printf("\nmp_read_radix(b) failed!");
+         return EXIT_FAILURE;
+      }
+      if (mp_read_radix(&c, should_, 16) != MP_OKAY) {
+         printf("\nmp_read_radix(should) failed!");
+         return EXIT_FAILURE;
+      }
+
+      if (mp_invmod(&a, &b, &d) != MP_OKAY) {
+         printf("\nmp_invmod() failed!");
+         return EXIT_FAILURE;
+      }
+
+      if (mp_cmp(&c, &d) != MP_EQ) {
+         printf("\nmp_invmod() bad result!");
+         return EXIT_FAILURE;
+      }
+   }
+
    // test mp_get_int
    printf("\n\nTesting: mp_get_int");
    for (i = 0; i < 1000; ++i) {

From f1b9bbf593051c6b1d7220758d9f1953f1ce9600 Mon Sep 17 00:00:00 2001
From: Karel Miko <karel.miko@gmail.com>
Date: Sat, 30 Jun 2018 15:48:40 +0200
Subject: [PATCH 2/2] bn_fast_mp_invmod fix related to #118

---
 bn_fast_mp_invmod.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/bn_fast_mp_invmod.c b/bn_fast_mp_invmod.c
index 91b5bf6..be1a810 100644
--- a/bn_fast_mp_invmod.c
+++ b/bn_fast_mp_invmod.c
@@ -138,6 +138,14 @@ top:
          goto LBL_ERR;
       }
    }
+
+   /* too big */
+   while (mp_cmp_mag(&D, b) != MP_LT) {
+      if ((res = mp_sub(&D, b, &D)) != MP_OKAY) {
+         goto LBL_ERR;
+      }
+   }
+
    mp_exch(&D, c);
    c->sign = neg;
    res = MP_OKAY;