From 08b17def58d4135c1dc904a6068670c3c92a3768 Mon Sep 17 00:00:00 2001
From: Karl-Johan Alm <karljohan-alm@garage.co.jp>
Date: Mon, 26 Feb 2018 15:34:53 +0900
Subject: [arith_uint256] Do not destroy *this content if passed-in operator
 may reference it

---
 src/arith_uint256.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/arith_uint256.cpp b/src/arith_uint256.cpp
index 65de632306..c7ddb17eb0 100644
--- a/src/arith_uint256.cpp
+++ b/src/arith_uint256.cpp
@@ -69,16 +69,16 @@ base_uint<BITS>& base_uint<BITS>::operator*=(uint32_t b32)
 template <unsigned int BITS>
 base_uint<BITS>& base_uint<BITS>::operator*=(const base_uint& b)
 {
-    base_uint<BITS> a = *this;
-    *this = 0;
+    base_uint<BITS> a;
     for (int j = 0; j < WIDTH; j++) {
         uint64_t carry = 0;
         for (int i = 0; i + j < WIDTH; i++) {
-            uint64_t n = carry + pn[i + j] + (uint64_t)a.pn[j] * b.pn[i];
-            pn[i + j] = n & 0xffffffff;
+            uint64_t n = carry + a.pn[i + j] + (uint64_t)pn[j] * b.pn[i];
+            a.pn[i + j] = n & 0xffffffff;
             carry = n >> 32;
         }
     }
+    *this = a;
     return *this;
 }
 
-- 
cgit v1.2.3


From b120f7bdbee83c00e46a9ec6d0cd09a816631f45 Mon Sep 17 00:00:00 2001
From: Karl-Johan Alm <karljohan-alm@garage.co.jp>
Date: Mon, 26 Feb 2018 15:34:11 +0900
Subject: [test] Add tests for self usage in arith_uint256

---
 src/test/uint256_tests.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/test/uint256_tests.cpp b/src/test/uint256_tests.cpp
index ad5478e829..20ed29f59b 100644
--- a/src/test/uint256_tests.cpp
+++ b/src/test/uint256_tests.cpp
@@ -266,4 +266,17 @@ BOOST_AUTO_TEST_CASE( conversion )
     BOOST_CHECK(R2L.GetHex() == UintToArith256(R2L).GetHex());
 }
 
+BOOST_AUTO_TEST_CASE( operator_with_self )
+{
+    arith_uint256 v = UintToArith256(uint256S("02"));
+    v *= v;
+    BOOST_CHECK(v == UintToArith256(uint256S("04")));
+    v /= v;
+    BOOST_CHECK(v == UintToArith256(uint256S("01")));
+    v += v;
+    BOOST_CHECK(v == UintToArith256(uint256S("02")));
+    v -= v;
+    BOOST_CHECK(v == UintToArith256(uint256S("0")));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
-- 
cgit v1.2.3