From e28cb67d41643bf2073e46149e6f5d10d1fd0ef5 Mon Sep 17 00:00:00 2001 From: Jade Lovelace Date: Fri, 5 Jul 2024 15:52:55 +0200 Subject: [PATCH] libutil: add checked arithmetic tools This is in preparation for adding checked arithmetic to the evaluator. Change-Id: I6e115ce8f5411feda1706624977a4dcd5efd4d13 --- src/libutil/checked-arithmetic.hh | 182 ++++++++++++++++++ src/libutil/meson.build | 1 + .../tests/gtest-with-params.hh | 54 ++++++ tests/unit/libutil/checked-arithmetic.cc | 158 +++++++++++++++ 4 files changed, 395 insertions(+) create mode 100644 src/libutil/checked-arithmetic.hh create mode 100644 tests/unit/libutil-support/tests/gtest-with-params.hh create mode 100644 tests/unit/libutil/checked-arithmetic.cc diff --git a/src/libutil/checked-arithmetic.hh b/src/libutil/checked-arithmetic.hh new file mode 100644 index 000000000..55d6ad205 --- /dev/null +++ b/src/libutil/checked-arithmetic.hh @@ -0,0 +1,182 @@ +#pragma once +/** + * @file Checked arithmetic with classes that make it hard to accidentally make something an unchecked operation. + */ + +#include +#include // IWYU pragma: keep +#include +#include +#include +#include +#include + +namespace nix::checked { + +class DivideByZero : std::exception +{}; + +/** + * Numeric value enforcing checked arithmetic. Performing mathematical operations on such values will return a Result + * type which needs to be checked. + */ +template +struct Checked +{ + using Inner = T; + + // TODO: this must be a "trivial default constructor", which means it + // cannot set the value to NOT DO UB on uninit. + T value; + + Checked() = default; + explicit Checked(T const value) + : value{value} + { + } + Checked(Checked const & other) = default; + Checked(Checked && other) = default; + Checked & operator=(Checked const & other) = default; + + std::strong_ordering operator<=>(Checked const & other) const = default; + std::strong_ordering operator<=>(T const & other) const + { + return value <=> other; + } + + explicit operator T() const + { + return value; + } + + enum class OverflowKind { + NoOverflow, + Overflow, + DivByZero, + }; + + class Result + { + T value; + OverflowKind overflowed_; + + public: + Result(T value, bool overflowed) + : value{value} + , overflowed_{overflowed ? OverflowKind::Overflow : OverflowKind::NoOverflow} + { + } + Result(T value, OverflowKind overflowed) + : value{value} + , overflowed_{overflowed} + { + } + + bool operator==(Result other) const + { + return value == other.value && overflowed_ == other.overflowed_; + } + + std::optional valueChecked() const + { + if (overflowed_ != OverflowKind::NoOverflow) { + return std::nullopt; + } else { + return value; + } + } + + /** + * Returns the result as if the arithmetic were performed as wrapping arithmetic. + * + * \throws DivideByZero if the operation was a divide by zero. + */ + T valueWrapping() const + { + if (overflowed_ == OverflowKind::DivByZero) { + throw DivideByZero{}; + } + return value; + } + + bool overflowed() const + { + return overflowed_ == OverflowKind::Overflow; + } + + bool divideByZero() const + { + return overflowed_ == OverflowKind::DivByZero; + } + }; + + Result operator+(Checked const other) const + { + return (*this) + other.value; + } + Result operator+(T const other) const + { + T result; + bool overflowed = __builtin_add_overflow(value, other, &result); + return Result{result, overflowed}; + } + + Result operator-(Checked const other) const + { + return (*this) - other.value; + } + Result operator-(T const other) const + { + T result; + bool overflowed = __builtin_sub_overflow(value, other, &result); + return Result{result, overflowed}; + } + + Result operator*(Checked const other) const + { + return (*this) * other.value; + } + Result operator*(T const other) const + { + T result; + bool overflowed = __builtin_mul_overflow(value, other, &result); + return Result{result, overflowed}; + } + + Result operator/(Checked const other) const + { + return (*this) / other.value; + } + /** + * Performs a checked division. + * + * If the right hand side is zero, the result is marked as a DivByZero and + * valueWrapping will throw. + */ + Result operator/(T const other) const + { + constexpr T const minV = std::numeric_limits::min(); + + // It's only possible to overflow with signed division since doing so + // requires crossing the two's complement limits by MIN / -1 (since + // two's complement has one more in range in the negative direction + // than in the positive one). + if (std::is_signed() && (value == minV && other == -1)) { + return Result{minV, true}; + } else if (other == 0) { + return Result{0, OverflowKind::DivByZero}; + } else { + T result = value / other; + return Result{result, false}; + } + } +}; + +template +std::ostream & operator<<(std::ostream & ios, Checked v) +{ + ios << v.value; + return ios; +} + +} diff --git a/src/libutil/meson.build b/src/libutil/meson.build index 8552c4c9d..e0299177f 100644 --- a/src/libutil/meson.build +++ b/src/libutil/meson.build @@ -171,6 +171,7 @@ headers = [config_h] + files( 'args/root.hh', 'callback.hh', 'canon-path.hh', + 'checked-arithmetic.hh', 'chunked-vector.hh', 'closure.hh', 'comparator.hh', diff --git a/tests/unit/libutil-support/tests/gtest-with-params.hh b/tests/unit/libutil-support/tests/gtest-with-params.hh new file mode 100644 index 000000000..323a083fe --- /dev/null +++ b/tests/unit/libutil-support/tests/gtest-with-params.hh @@ -0,0 +1,54 @@ +#pragma once +// SPDX-FileCopyrightText: 2014 Emil Eriksson +// +// SPDX-License-Identifier: BSD-2-Clause +// +// The lion's share of this code is copy pasted directly out of RapidCheck +// headers, so the copyright is set accordingly. +/** + * @file Implements the ability to run a RapidCheck test under gtest with changed + * test parameters such as the number of tests to run. This is useful for + * running very large numbers of the extremely cheap property tests. + */ + +#include +#include +#include + +namespace rc::detail { + +using MakeTestParams = TestParams (*)(); + +template +void checkGTestWith(Testable && testable, MakeTestParams makeTestParams) +{ + const auto testInfo = ::testing::UnitTest::GetInstance()->current_test_info(); + detail::TestMetadata metadata; + metadata.id = std::string(testInfo->test_case_name()) + "/" + std::string(testInfo->name()); + metadata.description = std::string(testInfo->name()); + + const auto result = checkTestable(std::forward(testable), metadata, makeTestParams()); + + if (result.template is()) { + const auto success = result.template get(); + if (!success.distribution.empty()) { + printResultMessage(result, std::cout); + std::cout << std::endl; + } + } else { + std::ostringstream ss; + printResultMessage(result, ss); + FAIL() << ss.str() << std::endl; + } +} +} + +#define RC_GTEST_PROP_WITH_PARAMS(TestCase, Name, MakeParams, ArgList) \ + void rapidCheck_propImpl_##TestCase##_##Name ArgList; \ + \ + TEST(TestCase, Name) \ + { \ + ::rc::detail::checkGTestWith(&rapidCheck_propImpl_##TestCase##_##Name, MakeParams); \ + } \ + \ + void rapidCheck_propImpl_##TestCase##_##Name ArgList diff --git a/tests/unit/libutil/checked-arithmetic.cc b/tests/unit/libutil/checked-arithmetic.cc new file mode 100644 index 000000000..75018660d --- /dev/null +++ b/tests/unit/libutil/checked-arithmetic.cc @@ -0,0 +1,158 @@ +#include +#include +#include +#include +#include +#include + +#include + +#include "tests/gtest-with-params.hh" + +namespace rc { +using namespace nix; + +template +struct Arbitrary> +{ + static Gen> arbitrary() + { + return gen::arbitrary(); + } +}; + +} + +namespace nix::checked { + +// Pointer to member function! Mildly gross. +template +using Oper = Checked::Result (Checked::*)(T const other) const; + +template +using ReferenceOper = T (*)(T a, T b); + +/** + * Checks that performing an operation that overflows into an inaccurate result + * has the desired behaviour. + * + * TBig is a type large enough to represent all results of TSmall operations. + */ +template +void checkType(TSmall a_, TSmall b, Oper oper, ReferenceOper reference) +{ + // Sufficient to fit all values + TBig referenceResult = reference(a_, b); + constexpr const TSmall minV = std::numeric_limits::min(); + constexpr const TSmall maxV = std::numeric_limits::max(); + + Checked a{a_}; + auto result = (a.*(oper))(b); + + // Just truncate it to get the in-range result + RC_ASSERT(result.valueWrapping() == static_cast(referenceResult)); + + if (referenceResult > maxV || referenceResult < minV) { + RC_ASSERT(result.overflowed()); + RC_ASSERT(!result.valueChecked().has_value()); + } else { + RC_ASSERT(!result.overflowed()); + RC_ASSERT(result.valueChecked().has_value()); + RC_ASSERT(*result.valueChecked() == referenceResult); + } +} + +/** + * Checks that performing an operation that overflows into an inaccurate result + * has the desired behaviour. + * + * TBig is a type large enough to represent all results of TSmall operations. + */ +template +void checkDivision(TSmall a_, TSmall b) +{ + // Sufficient to fit all values + constexpr const TSmall minV = std::numeric_limits::min(); + + Checked a{a_}; + auto result = a / b; + + if (std::is_signed() && a_ == minV && b == -1) { + // This is the only possible overflow condition + RC_ASSERT(result.valueWrapping() == minV); + RC_ASSERT(result.overflowed()); + } else if (b == 0) { + RC_ASSERT(result.divideByZero()); + RC_ASSERT_THROWS_AS(result.valueWrapping(), nix::checked::DivideByZero); + RC_ASSERT(result.valueChecked() == std::nullopt); + } else { + TBig referenceResult = a_ / b; + auto result_ = result.valueChecked(); + RC_ASSERT(result_.has_value()); + RC_ASSERT(*result_ == referenceResult); + RC_ASSERT(result.valueWrapping() == referenceResult); + } +} + +/** Creates parameters that perform a more adequate number of checks to validate + * extremely cheap tests such as arithmetic tests */ +static rc::detail::TestParams makeParams() +{ + auto const & conf = rc::detail::configuration(); + auto newParams = conf.testParams; + newParams.maxSuccess = 10000; + return newParams; +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, add_unsigned, makeParams, (uint16_t a, uint16_t b)) +{ + checkType(a, b, &Checked::operator+, [](int32_t a, int32_t b) { return a + b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, add_signed, makeParams, (int16_t a, int16_t b)) +{ + checkType(a, b, &Checked::operator+, [](int32_t a, int32_t b) { return a + b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, sub_unsigned, makeParams, (uint16_t a, uint16_t b)) +{ + checkType(a, b, &Checked::operator-, [](int32_t a, int32_t b) { return a - b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, sub_signed, makeParams, (int16_t a, int16_t b)) +{ + checkType(a, b, &Checked::operator-, [](int32_t a, int32_t b) { return a - b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, mul_unsigned, makeParams, (uint16_t a, uint16_t b)) +{ + checkType(a, b, &Checked::operator*, [](int64_t a, int64_t b) { return a * b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, mul_signed, makeParams, (int16_t a, int16_t b)) +{ + checkType(a, b, &Checked::operator*, [](int64_t a, int64_t b) { return a * b; }); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, div_unsigned, makeParams, (uint16_t a, uint16_t b)) +{ + checkDivision(a, b); +} + +RC_GTEST_PROP_WITH_PARAMS(Checked, div_signed, makeParams, (int16_t a, int16_t b)) +{ + checkDivision(a, b); +} + +// Make absolutely sure that we check the special cases if the proptest +// generator does not come up with them. This one is especially important +// because it has very specific pairs required for the edge cases unlike the +// others. +TEST(Checked, div_signed_special_cases) +{ + checkDivision(std::numeric_limits::min(), -1); + checkDivision(std::numeric_limits::min(), 0); + checkDivision(0, 0); +} + +}