From 7cd0664e602714300aefa36eb7bab24e8cac0a2f Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 21 Aug 2021 01:23:23 +0200
Subject: [PATCH] abacus: bignum: fix carry bug in addition

---
 src/bignum/bignum.cc | 4 ++++
 tests/unit/bignum.cc | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/src/bignum/bignum.cc b/src/bignum/bignum.cc
index 4c5b19f..2d99095 100644
--- a/src/bignum/bignum.cc
+++ b/src/bignum/bignum.cc
@@ -52,6 +52,10 @@ digits_type do_addition(digits_type const& lhs, digits_type const& rhs) {
         ++it;
     }
 
+    if (carry != 0) {
+        res.push_back(carry);
+    }
+
     return res;
 }
 
diff --git a/tests/unit/bignum.cc b/tests/unit/bignum.cc
index 8797633..31cf03a 100644
--- a/tests/unit/bignum.cc
+++ b/tests/unit/bignum.cc
@@ -115,6 +115,15 @@ TEST(BigNum, addition_flips_sign) {
     EXPECT_EQ(two + minus_one, one);
 }
 
+TEST(BigNum, addition_carry) {
+    auto const one = BigNum(1);
+    auto const nine = BigNum(9);
+    auto const ten = BigNum(10);
+
+    EXPECT_EQ(one + nine, ten);
+    EXPECT_EQ(nine + one, ten);
+}
+
 TEST(BigNum, substraction_positive) {
     auto const zero = BigNum(0);
     auto const one = BigNum(1);