From fac01888d17423d6c23a9ce15d98fc88fb34e3cc Mon Sep 17 00:00:00 2001
From: MarcoFalke <falke.marco@gmail.com>
Date: Tue, 2 Nov 2021 09:48:10 +0100
Subject: Move AdditionOverflow to util, Add CheckedAdd with unit tests

---
 src/Makefile.am                                 |  1 +
 src/test/fuzz/addition_overflow.cpp             |  1 +
 src/test/fuzz/crypto_chacha20_poly1305_aead.cpp |  1 +
 src/test/fuzz/integer.cpp                       |  1 +
 src/test/fuzz/pow.cpp                           |  1 +
 src/test/fuzz/util.cpp                          |  1 +
 src/test/fuzz/util.h                            | 11 ---------
 src/test/util_tests.cpp                         | 33 +++++++++++++++++++++++++
 src/util/overflow.h                             | 31 +++++++++++++++++++++++
 9 files changed, 70 insertions(+), 11 deletions(-)
 create mode 100644 src/util/overflow.h

diff --git a/src/Makefile.am b/src/Makefile.am
index 4199f7e89d..994038a03b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -248,6 +248,7 @@ BITCOIN_CORE_H = \
   util/macros.h \
   util/message.h \
   util/moneystr.h \
+  util/overflow.h \
   util/overloaded.h \
   util/rbf.h \
   util/readwritefile.h \
diff --git a/src/test/fuzz/addition_overflow.cpp b/src/test/fuzz/addition_overflow.cpp
index c6cfbd8d30..cfad41659e 100644
--- a/src/test/fuzz/addition_overflow.cpp
+++ b/src/test/fuzz/addition_overflow.cpp
@@ -5,6 +5,7 @@
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <util/overflow.h>
 
 #include <cstdint>
 #include <string>
diff --git a/src/test/fuzz/crypto_chacha20_poly1305_aead.cpp b/src/test/fuzz/crypto_chacha20_poly1305_aead.cpp
index 5e60b0f25b..596614a71b 100644
--- a/src/test/fuzz/crypto_chacha20_poly1305_aead.cpp
+++ b/src/test/fuzz/crypto_chacha20_poly1305_aead.cpp
@@ -7,6 +7,7 @@
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <util/overflow.h>
 
 #include <cassert>
 #include <cstdint>
diff --git a/src/test/fuzz/integer.cpp b/src/test/fuzz/integer.cpp
index ce424c443e..4999d87f9d 100644
--- a/src/test/fuzz/integer.cpp
+++ b/src/test/fuzz/integer.cpp
@@ -26,6 +26,7 @@
 #include <univalue.h>
 #include <util/check.h>
 #include <util/moneystr.h>
+#include <util/overflow.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/system.h>
diff --git a/src/test/fuzz/pow.cpp b/src/test/fuzz/pow.cpp
index 1123c8c170..0004d82d66 100644
--- a/src/test/fuzz/pow.cpp
+++ b/src/test/fuzz/pow.cpp
@@ -9,6 +9,7 @@
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <util/overflow.h>
 
 #include <cstdint>
 #include <optional>
diff --git a/src/test/fuzz/util.cpp b/src/test/fuzz/util.cpp
index 843b29b911..5520eee758 100644
--- a/src/test/fuzz/util.cpp
+++ b/src/test/fuzz/util.cpp
@@ -8,6 +8,7 @@
 #include <pubkey.h>
 #include <test/fuzz/util.h>
 #include <test/util/script.h>
+#include <util/overflow.h>
 #include <util/rbf.h>
 #include <util/time.h>
 #include <version.h>
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
index 7937315822..f4f8e9e70d 100644
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -193,17 +193,6 @@ template <typename T>
     }
 }
 
-template <class T>
-[[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
-{
-    static_assert(std::is_integral<T>::value, "Integral required.");
-    if (std::numeric_limits<T>::is_signed) {
-        return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
-               (i < 0 && j < std::numeric_limits<T>::min() - i);
-    }
-    return std::numeric_limits<T>::max() - i < j;
-}
-
 [[nodiscard]] bool ContainsSpentInput(const CTransaction& tx, const CCoinsViewCache& inputs) noexcept;
 
 /**
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 9540cead24..bc3ef9f7f1 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -15,6 +15,7 @@
 #include <util/getuniquepath.h>
 #include <util/message.h> // For MessageSign(), MessageVerify(), MESSAGE_MAGIC
 #include <util/moneystr.h>
+#include <util/overflow.h>
 #include <util/spanparsing.h>
 #include <util/strencodings.h>
 #include <util/string.h>
@@ -1463,6 +1464,38 @@ BOOST_AUTO_TEST_CASE(test_IsDigit)
     BOOST_CHECK_EQUAL(IsDigit(9), false);
 }
 
+/* Check for overflow */
+template <typename T>
+static void TestAddMatrixOverflow()
+{
+    constexpr T MAXI{std::numeric_limits<T>::max()};
+    BOOST_CHECK(!CheckedAdd(T{1}, MAXI));
+    BOOST_CHECK(!CheckedAdd(MAXI, MAXI));
+    BOOST_CHECK_EQUAL(0, CheckedAdd(T{0}, T{0}).value());
+    BOOST_CHECK_EQUAL(MAXI, CheckedAdd(T{0}, MAXI).value());
+    BOOST_CHECK_EQUAL(MAXI, CheckedAdd(T{1}, MAXI - 1).value());
+}
+
+/* Check for overflow or underflow */
+template <typename T>
+static void TestAddMatrix()
+{
+    TestAddMatrixOverflow<T>();
+    constexpr T MINI{std::numeric_limits<T>::min()};
+    constexpr T MAXI{std::numeric_limits<T>::max()};
+    BOOST_CHECK(!CheckedAdd(T{-1}, MINI));
+    BOOST_CHECK(!CheckedAdd(MINI, MINI));
+    BOOST_CHECK_EQUAL(MINI, CheckedAdd(T{0}, MINI).value());
+    BOOST_CHECK_EQUAL(MINI, CheckedAdd(T{-1}, MINI + 1).value());
+    BOOST_CHECK_EQUAL(-1, CheckedAdd(MINI, MAXI).value());
+}
+
+BOOST_AUTO_TEST_CASE(util_overflow)
+{
+    TestAddMatrixOverflow<unsigned>();
+    TestAddMatrix<signed>();
+}
+
 BOOST_AUTO_TEST_CASE(test_ParseInt32)
 {
     int32_t n;
diff --git a/src/util/overflow.h b/src/util/overflow.h
new file mode 100644
index 0000000000..5982af8d04
--- /dev/null
+++ b/src/util/overflow.h
@@ -0,0 +1,31 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_OVERFLOW_H
+#define BITCOIN_UTIL_OVERFLOW_H
+
+#include <limits>
+#include <type_traits>
+
+template <class T>
+[[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
+{
+    static_assert(std::is_integral<T>::value, "Integral required.");
+    if (std::numeric_limits<T>::is_signed) {
+        return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
+               (i < 0 && j < std::numeric_limits<T>::min() - i);
+    }
+    return std::numeric_limits<T>::max() - i < j;
+}
+
+template <class T>
+[[nodiscard]] std::optional<T> CheckedAdd(const T i, const T j) noexcept
+{
+    if (AdditionOverflow(i, j)) {
+        return std::nullopt;
+    }
+    return i + j;
+}
+
+#endif // BITCOIN_UTIL_OVERFLOW_H
-- 
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