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Don't memcmp(x, y, -1) from ranges::lexicographical_compare #3989

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Aug 31, 2023
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Don't memcmp(x, y, -1) from ranges::lexicographical_compare #3989

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2621080
Avoid `memcmp(x, y, -1)` with ASan
CaseyCarter Aug 14, 2023
6e099db
Don't call `memcmp(x,y,-1)` with two "infinite" ranges from `lexicogr…
CaseyCarter Aug 25, 2023
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2 changes: 1 addition & 1 deletion stl/inc/algorithm
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Original file line number Diff line number Diff line change
Expand Up @@ -10654,7 +10654,7 @@ namespace ranges {
constexpr bool _Is_sized2 = sized_sentinel_for<_Se2, _It2>;
if constexpr (!is_void_v<_Memcmp_classification_pred> && _Sized_or_unreachable_sentinel_for<_Se1, _It1>
&& _Sized_or_unreachable_sentinel_for<_Se2, _It2> && same_as<_Pj1, identity>
&& same_as<_Pj2, identity>) {
&& same_as<_Pj2, identity> && (_Is_sized1 || _Is_sized2)) {
if (!_STD is_constant_evaluated()) {
size_t _Num1;
if constexpr (_Is_sized1) {
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62 changes: 35 additions & 27 deletions tests/std/tests/P0896R4_ranges_alg_lexicographical_compare/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -194,40 +194,46 @@ struct instantiator {
empty1.begin(), empty1.end(), empty2.begin(), empty2.end(), less{}, get_first, get_second);
assert(!result);
}
{ // Validate memcmp case
unsigned char arr1[3]{0, 1, 2};
unsigned char arr2[3]{0, 1, 3};
assert(lexicographical_compare(arr1, arr2));
arr2[2] = 2;
assert(!lexicographical_compare(arr1, arr2));
arr2[2] = 1;
assert(!lexicographical_compare(arr1, arr2));
}
{ // Validate memcmp + unreachable_sentinel cases
unsigned char arr1[3]{0, 1, 2};
unsigned char arr2[3]{0, 1, 3};

assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr1), unreachable_sentinel));
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr1), end(arr1)));

assert(lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), unreachable_sentinel));
assert(lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
arr2[2] = 2;
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
arr2[2] = 1;
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), unreachable_sentinel));
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(!lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
}
}
};

constexpr void concrete_tests() {
using ranges::lexicographical_compare, ranges::begin, ranges::end;

{ // Validate memcmp case
unsigned char arr1[3]{0, 1, 2};
unsigned char arr2[3]{0, 1, 3};
assert(lexicographical_compare(arr1, arr2));
arr2[2] = 2;
assert(!lexicographical_compare(arr1, arr2));
arr2[2] = 1;
assert(!lexicographical_compare(arr1, arr2));
}
{ // Validate memcmp + unreachable_sentinel cases
unsigned char arr1[3]{0, 1, 2};
unsigned char arr2[3]{0, 1, 3};

assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr1), unreachable_sentinel));
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr1), end(arr1)));

assert(lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), unreachable_sentinel));
assert(lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
arr2[2] = 2;
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
arr2[2] = 1;
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), unreachable_sentinel));
assert(!lexicographical_compare(begin(arr1), unreachable_sentinel, begin(arr2), end(arr2)));
assert(!lexicographical_compare(begin(arr1), end(arr1), begin(arr2), unreachable_sentinel));
}
}

#ifdef TEST_EVERYTHING
int main() {
// No constexpr tests here: we hit the constexpr step limits too quickly.
test_in_in<instantiator, const P, const P>();
concrete_tests();
}
#else // ^^^ test all range combinations / test only interesting combinations vvv
template <test::ProxyRef IsProxy>
Expand All @@ -243,6 +249,8 @@ constexpr void run_tests() {
instantiator::call<range_type<ProxyRef::yes>, range_type<ProxyRef::no>>();
instantiator::call<range_type<ProxyRef::no>, range_type<ProxyRef::yes>>();
instantiator::call<range_type<ProxyRef::no>, range_type<ProxyRef::no>>();

concrete_tests();
}

int main() {
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