1  // Copyright (c) 2025-present The Bitcoin Core developers
 2  // Distributed under the MIT software license, see the accompanying
 3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 4  
 5  #include <test/fuzz/FuzzedDataProvider.h>
 6  #include <test/fuzz/fuzz.h>
 7  #include <util/check.h>
 8  #include <util/overflow.h>
 9  
10  #include <algorithm>
11  #include <limits>
12  #include <optional>
13  
14  namespace {
15  //! Test overflow operations for type T using a wider type, W, to verify results.
16  template <typename T, typename W>
17  void TestOverflow(FuzzedDataProvider& fuzzed_data_provider)
18  {
19      constexpr auto min{std::numeric_limits<T>::min()};
20      constexpr auto max{std::numeric_limits<T>::max()};
21      // Range needs to be at least twice as big to allow two numbers to be added without overflowing.
22      static_assert(min >= std::numeric_limits<W>::min() / 2);
23      static_assert(max <= std::numeric_limits<W>::max() / 2);
24  
25      auto widen = [](T value) -> W { return value; };
26      auto clamp = [](W value) -> W { return std::clamp<W>(value, min, max); };
27      auto check = [](W value) -> std::optional<W> { if (value >= min && value <= max) return value; else return std::nullopt; };
28  
29      const T i = fuzzed_data_provider.ConsumeIntegral<T>();
30      const T j = fuzzed_data_provider.ConsumeIntegral<T>();
31      const unsigned shift = fuzzed_data_provider.ConsumeIntegralInRange<unsigned>(0, std::numeric_limits<W>::digits - std::numeric_limits<T>::digits);
32  
33      Assert(clamp(widen(i) + widen(j)) == SaturatingAdd(i, j));
34      Assert(check(widen(i) + widen(j)) == CheckedAdd(i, j));
35  
36      Assert(clamp(widen(i) << shift) == SaturatingLeftShift(i, shift));
37      Assert(check(widen(i) << shift) == CheckedLeftShift(i, shift));
38  }
39  } // namespace
40  
41  FUZZ_TARGET(overflow)
42  {
43      FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
44      TestOverflow<int8_t, int64_t>(fuzzed_data_provider);
45      TestOverflow<int16_t, int64_t>(fuzzed_data_provider);
46      TestOverflow<int32_t, int64_t>(fuzzed_data_provider);
47      TestOverflow<uint8_t, uint64_t>(fuzzed_data_provider);
48      TestOverflow<uint16_t, uint64_t>(fuzzed_data_provider);
49      TestOverflow<uint32_t, uint64_t>(fuzzed_data_provider);
50  }