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Merge bitcoin/bitcoin#24224: util: Add SaturatingAdd helper

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faa7d8a3f7cba02eca7e247108a6b98ea9daf373 util: Add SaturatingAdd helper (MarcoFalke)

Pull request description:

  Seems good to have this in the repo, as it might be needed to write cleaner code. For example:

  * https://github.com/bitcoin/bitcoin/pull/24090#issuecomment-1019948200
  * https://github.com/bitcoin/bitcoin/pull/23418#discussion_r744953272
  * ...

ACKs for top commit:
  MarcoFalke:
    Added a test. Should be trivial to re-ACK with `git range-diff bitcoin-core/master fa90189cbf faa7d8a3f7`
  klementtan:
    reACK faa7d8a3f7
  vasild:
    ACK faa7d8a3f7cba02eca7e247108a6b98ea9daf373

Tree-SHA512: d0e6efdba7dfcbdd16ab4539a7f5e45a97d17792e42586c3c52caaae3fc70612dc9e364359658de5de5718fb8c2a765a59ceb2230098355394fa067a9732bc2a
This commit is contained in:
MarcoFalke 2022-02-21 15:50:59 +01:00 committed by pasta
parent b1fcab4f42
commit b9b854663a
No known key found for this signature in database
GPG Key ID: 52527BEDABE87984
3 changed files with 48 additions and 5 deletions
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17
src/test/fuzz/addition_overflow.cpp
View File

@ -26,6 +26,12 @@ void TestAdditionOverflow(FuzzedDataProvider& fuzzed_data_provider)
const T i = fuzzed_data_provider.ConsumeIntegral<T>();
const T j = fuzzed_data_provider.ConsumeIntegral<T>();
const bool is_addition_overflow_custom = AdditionOverflow(i, j);
const auto maybe_add{CheckedAdd(i, j)};
const auto sat_add{SaturatingAdd(i, j)};
assert(is_addition_overflow_custom == !maybe_add.has_value());
assert(is_addition_overflow_custom == AdditionOverflow(j, i));
assert(maybe_add == CheckedAdd(j, i));
assert(sat_add == SaturatingAdd(j, i));
#if defined(HAVE_BUILTIN_ADD_OVERFLOW)
T result_builtin;
const bool is_addition_overflow_builtin = __builtin_add_overflow(i, j, &result_builtin);
@ -33,11 +39,14 @@ void TestAdditionOverflow(FuzzedDataProvider& fuzzed_data_provider)
if (!is_addition_overflow_custom) {
assert(i + j == result_builtin);
}
#else
if (!is_addition_overflow_custom) {
(void)(i + j);
}
#endif
if (is_addition_overflow_custom) {
assert(sat_add == std::numeric_limits<T>::min() || sat_add == std::numeric_limits<T>::max());
} else {
const auto add{i + j};
assert(add == maybe_add.value());
assert(add == sat_add);
}
}
} // namespace

16
src/test/util_tests.cpp
View File

@ -1506,9 +1506,17 @@ 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(MAXI, SaturatingAdd(T{1}, MAXI));
BOOST_CHECK_EQUAL(MAXI, SaturatingAdd(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());
BOOST_CHECK_EQUAL(MAXI - 1, CheckedAdd(T{1}, MAXI - 2).value());
BOOST_CHECK_EQUAL(0, SaturatingAdd(T{0}, T{0}));
BOOST_CHECK_EQUAL(MAXI, SaturatingAdd(T{0}, MAXI));
BOOST_CHECK_EQUAL(MAXI, SaturatingAdd(T{1}, MAXI - 1));
BOOST_CHECK_EQUAL(MAXI - 1, SaturatingAdd(T{1}, MAXI - 2));
}
/* Check for overflow or underflow */
@ -1520,9 +1528,17 @@ static void TestAddMatrix()
constexpr T MAXI{std::numeric_limits<T>::max()};
BOOST_CHECK(!CheckedAdd(T{-1}, MINI));
BOOST_CHECK(!CheckedAdd(MINI, MINI));
BOOST_CHECK_EQUAL(MINI, SaturatingAdd(T{-1}, MINI));
BOOST_CHECK_EQUAL(MINI, SaturatingAdd(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_CHECK_EQUAL(MINI + 1, CheckedAdd(T{-1}, MINI + 2).value());
BOOST_CHECK_EQUAL(MINI, SaturatingAdd(T{0}, MINI));
BOOST_CHECK_EQUAL(MINI, SaturatingAdd(T{-1}, MINI + 1));
BOOST_CHECK_EQUAL(MINI + 1, SaturatingAdd(T{-1}, MINI + 2));
BOOST_CHECK_EQUAL(-1, SaturatingAdd(MINI, MAXI));
}
BOOST_AUTO_TEST_CASE(util_overflow)

20
src/util/overflow.h
View File

@ -13,7 +13,7 @@ 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) {
if constexpr (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);
}
@ -29,4 +29,22 @@ template <class T>
return i + j;
}
template <class T>
[[nodiscard]] T SaturatingAdd(const T i, const T j) noexcept
{
if constexpr (std::numeric_limits<T>::is_signed) {
if (i > 0 && j > std::numeric_limits<T>::max() - i) {
return std::numeric_limits<T>::max();
}
if (i < 0 && j < std::numeric_limits<T>::min() - i) {
return std::numeric_limits<T>::min();
}
} else {
if (std::numeric_limits<T>::max() - i < j) {
return std::numeric_limits<T>::max();
}
}
return i + j;
}
#endif // BITCOIN_UTIL_OVERFLOW_H