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Implement (chunk_view<forward>|stride_view)::iterator::operator(\+=|-=) in O(1) #3023

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Aug 12, 2022
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Implement (chunk_view<forward>|stride_view)::iterator::operator(\+=|-=) in O(1) #3023

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917c274
Implement `(chunk_view<forward>|stride_view)::iterator::operator(\+=|…
CaseyCarter Aug 10, 2022
61cc007
STL's review comment
CaseyCarter Aug 11, 2022
79383d0
With random_access_range, subtract instead of distance().
StephanTLavavej Aug 11, 2022
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59 changes: 36 additions & 23 deletions stl/inc/ranges
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Original file line number Diff line number Diff line change
Expand Up @@ -5566,35 +5566,35 @@ namespace ranges {
requires random_access_range<_Base> {
if (_Off > 0) {
#if _ITERATOR_DEBUG_LEVEL != 0
_STL_VERIFY(_Off == 1 || _Count <= (numeric_limits<difference_type>::max)() / (_Off - 1),
_STL_VERIFY(_Count <= (numeric_limits<difference_type>::max)() / _Off,
"cannot advance chunk_view iterator past end (integer overflow)");
_STL_VERIFY(_RANGES distance(_Current, _End) > _Count * (_Off - 1),
"cannot advance chunk_view iterator past end");
if constexpr (sized_sentinel_for<_Base_sentinel, _Base_iterator>) {
_STL_VERIFY(_End - _Current > _Count * (_Off - 1), //
"cannot advance chunk_view iterator past end");
}
#endif // _ITERATOR_DEBUG_LEVEL != 0
_Missing = _RANGES advance(_Current, _Count * _Off, _End);

// Per to-be-filed LWG issue (See GH-2995)
if constexpr (sized_sentinel_for<_Base_sentinel, _Base_iterator>) {
_Missing = _RANGES advance(_Current, _Count * _Off, _End);
} else {
_Current += static_cast<difference_type>(_Count * (_Off - 1));
_Missing = _RANGES advance(_Current, _Count, _End);
}
} else if (_Off < 0) {
_RANGES advance(_Current, _Count * _Off + _Missing);
_Current += static_cast<difference_type>(_Count * _Off + _Missing);
_Missing = 0;
}
return *this;
}

constexpr _Iterator& operator-=(const difference_type _Raw_off) /* not strengthened, see _RANGES advance */
constexpr _Iterator& operator-=(const difference_type _Off) /* not strengthened, see _RANGES advance */
requires random_access_range<_Base> {
const difference_type _Off = -_Raw_off;
if (_Off > 0) {
#if _ITERATOR_DEBUG_LEVEL != 0
_STL_VERIFY(_Off == 1 || _Count <= (numeric_limits<difference_type>::max)() / (_Off - 1),
"cannot advance chunk_view iterator past end (integer overflow)");
_STL_VERIFY(_RANGES distance(_Current, _End) > _Count * (_Off - 1),
"cannot advance chunk_view iterator past end");
_STL_VERIFY(_Off != (numeric_limits<difference_type>::min)(),
"cannot advance chunk_view iterator past end (integer overflow)");
#endif // _ITERATOR_DEBUG_LEVEL != 0
_Missing = _RANGES advance(_Current, _Count * _Off, _End);
} else if (_Off < 0) {
_RANGES advance(_Current, _Count * _Off + _Missing);
_Missing = 0;
}
return *this;
return *this += -_Off;
}

_NODISCARD constexpr value_type operator[](const difference_type _Off) const
Expand Down Expand Up @@ -6470,20 +6470,33 @@ namespace ranges {
constexpr _Iterator& operator+=(const difference_type _Off) requires random_access_range<_Base> {
if (_Off > 0) {
#if _ITERATOR_DEBUG_LEVEL != 0
_STL_VERIFY(_Off == 1 || _Stride <= (numeric_limits<difference_type>::max)() / (_Off - 1),
_STL_VERIFY(_Stride <= (numeric_limits<difference_type>::max)() / _Off,
"cannot advance stride_view iterator past end (integer overflow)");
_STL_VERIFY(_RANGES distance(_Current, _End) > _Stride * (_Off - 1),
"cannot advance stride_view iterator past end");
if constexpr (sized_sentinel_for<_Base_sentinel, _Base_iterator>) {
_STL_VERIFY(_End - _Current > _Stride * (_Off - 1), //
"cannot advance stride_view iterator past end");
}
#endif // _ITERATOR_DEBUG_LEVEL != 0
_Missing = _RANGES advance(_Current, _Stride * _Off, _End);

// Per to-be-filed LWG issue (See GH-2995)
if constexpr (sized_sentinel_for<_Base_sentinel, _Base_iterator>) {
_Missing = _RANGES advance(_Current, _Stride * _Off, _End);
} else {
_Current += static_cast<difference_type>(_Stride * (_Off - 1));
_Missing = _RANGES advance(_Current, _Stride, _End);
}
} else if (_Off < 0) {
_RANGES advance(_Current, _Stride * _Off + _Missing);
_Current += static_cast<difference_type>(_Stride * _Off + _Missing);
_Missing = 0;
}
return *this;
}

constexpr _Iterator& operator-=(const difference_type _Off) requires random_access_range<_Base> {
#if _ITERATOR_DEBUG_LEVEL != 0
_STL_VERIFY(_Off != (numeric_limits<difference_type>::min)(),
"cannot advance stride_view iterator past end (integer overflow)");
#endif // _ITERATOR_DEBUG_LEVEL != 0
return *this += -_Off;
}

Expand Down
7 changes: 7 additions & 0 deletions tests/std/tests/P1899R3_views_stride_death/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,12 @@ void test_iterator_advance_past_end_with_integer_overflow() {
it += (numeric_limits<ptrdiff_t>::max)() / 2; // cannot advance stride_view iterator past end (integer overflow)
}

void test_iterator_advance_negative_min() {
auto v = ranges::stride_view(some_ints, 3);
auto it = v.begin();
it -= (numeric_limits<ptrdiff_t>::min)(); // cannot advance stride_view iterator past end (integer overflow)
}

int main(int argc, char* argv[]) {
std_testing::death_test_executive exec;

Expand All @@ -58,6 +64,7 @@ int main(int argc, char* argv[]) {
test_iterator_postincrement_past_end,
test_iterator_advance_past_end,
test_iterator_advance_past_end_with_integer_overflow,
test_iterator_advance_negative_min,
});
#else // ^^^ test everything / test only _CONTAINER_DEBUG_LEVEL case vvv
exec.add_death_tests({
Expand Down
21 changes: 21 additions & 0 deletions tests/std/tests/P2442R1_views_chunk_death/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,24 @@ void test_inner_iterator_dereference_at_end() {
(void) *it; // cannot dereference chunk_view end iterator
}

void test_fwd_iterator_advance_past_end() {
auto v = chunk_view{span{some_ints}, 2};
auto it = v.begin();
it += 5; // cannot advance chunk_view iterator past end
}

void test_fwd_iterator_advance_past_end_with_integer_overflow() {
auto v = chunk_view{span{some_ints}, 2};
auto it = v.begin();
it += (numeric_limits<ptrdiff_t>::max)() / 2; // cannot advance chunk_view iterator past end (integer overflow)
}

void test_fwd_iterator_advance_negative_min() {
auto v = chunk_view{span{some_ints}, 2};
auto it = v.begin();
it -= (numeric_limits<ptrdiff_t>::min)(); // cannot advance chunk_view iterator past end (integer overflow)
}

int main(int argc, char* argv[]) {
std_testing::death_test_executive exec;

Expand All @@ -88,6 +106,9 @@ int main(int argc, char* argv[]) {
test_inner_iterator_postincrement_past_end,
test_outer_iterator_dereference_at_end,
test_inner_iterator_dereference_at_end,
test_fwd_iterator_advance_past_end,
test_fwd_iterator_advance_past_end_with_integer_overflow,
test_fwd_iterator_advance_negative_min,
});
#else // ^^^ test everything / test only _CONTAINER_DEBUG_LEVEL cases vvv
exec.add_death_tests({
Expand Down