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[libc++] Slightly simplify max_size and add new tests for vector #119990

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Merged
merged 2 commits into from
Feb 6, 2025
Merged

[libc++] Slightly simplify max_size and add new tests for vector #119990

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15e39e1
Slightly simplify max_size and add new tests for vector
winner245 Dec 14, 2024
9dc3a89
Make tests portable
winner245 Jan 29, 2025
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6 changes: 2 additions & 4 deletions libcxx/include/__vector/vector_bool.h
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Original file line number Diff line number Diff line change
Expand Up @@ -533,10 +533,8 @@ template <class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20 typename vector<bool, _Allocator>::size_type
vector<bool, _Allocator>::max_size() const _NOEXCEPT {
size_type __amax = __storage_traits::max_size(__alloc_);
size_type __nmax = numeric_limits<size_type>::max() / 2; // end() >= begin(), always
if (__nmax / __bits_per_word <= __amax)
return __nmax;
return __internal_cap_to_external(__amax);
size_type __nmax = numeric_limits<difference_type>::max();
return __nmax / __bits_per_word <= __amax ? __nmax : __internal_cap_to_external(__amax);
}

// Precondition: __new_size > capacity()
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105 changes: 105 additions & 0 deletions libcxx/test/std/containers/sequences/vector.bool/max_size.pass.cpp
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@@ -0,0 +1,105 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <vector>
// vector<bool>

// size_type max_size() const;

#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <limits>
#include <memory>
#include <type_traits>
#include <vector>

#include "min_allocator.h"
#include "sized_allocator.h"
#include "test_allocator.h"
#include "test_macros.h"

#if TEST_STD_VER >= 11

template <typename Alloc>
TEST_CONSTEXPR_CXX20 void test(const std::vector<bool, Alloc>& v) {
using Vector = std::vector<bool, Alloc>;
using size_type = typename Vector::size_type;
using difference_type = typename Vector::difference_type;
const size_type max_dist = static_cast<size_type>(std::numeric_limits<difference_type>::max());
assert(v.max_size() <= max_dist);

// The following check is specific to libc++ implementation details and is not portable to libstdc++
// and MSVC STL, as they use different types for the underlying word storage.
# if defined(_LIBCPP_VERSION)
using storage_type = typename Vector::__storage_type;
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This alias only exists in libc++, and our test suite must be portable. I suspect this means you will need to significantly weaken the tests for non-libc++ implementations, and that's okay. But the tests should still work on non-libc++ implementations.

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I've made part of the test libc++ only because libstdc++'s implementation is slightly different from libc++. The return values in the two implementations are, in math form (assuming no overflow)

min(numeric_limits<difference_type>::max() - bits_per_word + 1, alloc_traits::max_size() * bits_per_word); // libstdc++
min(numeric_limits<difference_type>::max(), alloc_traits::max_size() * bits_per_word); // libc++, MSVC-STL

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@winner245 winner245 Jan 30, 2025 •
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Another reason why this test is not fully portable to other standard implementations is that libc++, libstdc++, and MSVC-STL all use different word types for vector<bool> underlying storage:

Compiler Word Storage Type
MSVC unsigned int (fixed)
libstdc++ unsigned long (fixed)
libc++ alloc_traits::size_type (configurable through custom allocator)

using storage_alloc = typename std::allocator_traits<Alloc>::template rebind_alloc<storage_type>;
using storage_traits = typename std::allocator_traits<Alloc>::template rebind_traits<storage_type>;
const size_type max_alloc = storage_traits::max_size(storage_alloc(v.get_allocator()));
std::size_t bits_per_word = sizeof(storage_type) * CHAR_BIT;
const size_type max_size = max_dist / bits_per_word < max_alloc ? max_dist : max_alloc * bits_per_word;
assert(v.max_size() / bits_per_word <= max_alloc); // max_alloc * bits_per_word may overflow
assert(v.max_size() == max_size);
# endif // defined(_LIBCPP_VERSION)
}

#endif // TEST_STD_VER >= 11

TEST_CONSTEXPR_CXX20 bool tests() {
// The following check is specific to libc++ implementation details and is not portable to libstdc++
// and MSVC STL, as they use different types for the underlying word storage.
#if defined(_LIBCPP_VERSION)
// Test cases where v.max_size() is determined by allocator::max_size()
{
using Alloc = limited_allocator<bool, 10>;
using Vector = std::vector<bool, Alloc>;
using storage_type = Vector::__storage_type;
Vector v;
std::size_t bits_per_word = sizeof(storage_type) * CHAR_BIT;
assert(v.max_size() == 10 * bits_per_word);
}
#endif // defined(_LIBCPP_VERSION)

#if TEST_STD_VER >= 11

// Test with various allocators and different `size_type`s
{
test(std::vector<bool>());
test(std::vector<bool, std::allocator<int> >());
test(std::vector<bool, min_allocator<bool> >());
test(std::vector<bool, test_allocator<bool> >(test_allocator<bool>(1)));
test(std::vector<bool, other_allocator<bool> >(other_allocator<bool>(5)));
test(std::vector<bool, sized_allocator<bool, std::uint8_t, std::int8_t> >());
test(std::vector<bool, sized_allocator<bool, std::uint16_t, std::int16_t> >());
test(std::vector<bool, sized_allocator<bool, std::uint32_t, std::int32_t> >());
test(std::vector<bool, sized_allocator<bool, std::uint64_t, std::int64_t> >());
test(std::vector<bool, limited_allocator<bool, static_cast<std::size_t>(-1)> >());
}

// Test cases to identify incorrect implementations that unconditionally compute an internal-to-external
// capacity in a way that can overflow, leading to incorrect results.
{
test(std::vector<bool, limited_allocator<bool, static_cast<std::size_t>(-1) / 61> >());
test(std::vector<bool, limited_allocator<bool, static_cast<std::size_t>(-1) / 63> >());
}

#endif // TEST_STD_VER >= 11

return true;
}

int main(int, char**) {
tests();

#if TEST_STD_VER >= 20
static_assert(tests());
#endif

return 0;
}
53 changes: 46 additions & 7 deletions libcxx/test/std/containers/sequences/vector/vector.capacity/max_size.pass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10,16 +10,36 @@

// size_type max_size() const;

#include <algorithm>
#include <cassert>
#include <cstdint>
#include <limits>
#include <type_traits>
#include <vector>

#include "min_allocator.h"
#include "sized_allocator.h"
#include "test_allocator.h"
#include "test_macros.h"

#if TEST_STD_VER >= 11

TEST_CONSTEXPR_CXX20 bool test() {
template <typename T, typename Alloc>
TEST_CONSTEXPR_CXX20 void test(const std::vector<T, Alloc>& v) {
using Vector = std::vector<T, Alloc>;
using alloc_traits = std::allocator_traits<typename Vector::allocator_type>;
using size_type = typename Vector::size_type;
using difference_type = typename Vector::difference_type;
const size_type max_dist = static_cast<size_type>(std::numeric_limits<difference_type>::max());
const size_type max_alloc = alloc_traits::max_size(v.get_allocator());
assert(v.max_size() <= max_dist);
assert(v.max_size() <= max_alloc);
LIBCPP_ASSERT(v.max_size() == std::min<size_type>(max_dist, max_alloc));
}

#endif // TEST_STD_VER >= 11

TEST_CONSTEXPR_CXX20 bool tests() {
{
typedef limited_allocator<int, 10> A;
typedef std::vector<int, A> C;
Expand All @@ -30,29 +50,48 @@ TEST_CONSTEXPR_CXX20 bool test() {
{
typedef limited_allocator<int, (std::size_t)-1> A;
typedef std::vector<int, A> C;
const C::size_type max_dist =
static_cast<C::size_type>(std::numeric_limits<C::difference_type>::max());
const C::size_type max_dist = static_cast<C::size_type>(std::numeric_limits<C::difference_type>::max());
C c;
assert(c.max_size() <= max_dist);
LIBCPP_ASSERT(c.max_size() == max_dist);
}
{
typedef std::vector<char> C;
const C::size_type max_dist =
static_cast<C::size_type>(std::numeric_limits<C::difference_type>::max());
const C::size_type max_dist = static_cast<C::size_type>(std::numeric_limits<C::difference_type>::max());
C c;
assert(c.max_size() <= max_dist);
assert(c.max_size() <= alloc_max_size(c.get_allocator()));
LIBCPP_ASSERT(c.max_size() == std::min(max_dist, alloc_max_size(c.get_allocator())));
}

#if TEST_STD_VER >= 11

// Test with various allocators and diffrent size_type
{
test(std::vector<int>());
test(std::vector<short, std::allocator<short> >());
test(std::vector<unsigned, min_allocator<unsigned> >());
test(std::vector<char, test_allocator<char> >(test_allocator<char>(1)));
test(std::vector<std::size_t, other_allocator<std::size_t> >(other_allocator<std::size_t>(5)));
test(std::vector<int, sized_allocator<int, std::uint8_t, std::int8_t> >());
test(std::vector<int, sized_allocator<int, std::uint16_t, std::int16_t> >());
test(std::vector<int, sized_allocator<int, std::uint32_t, std::int32_t> >());
test(std::vector<int, sized_allocator<int, std::uint64_t, std::int64_t> >());
test(std::vector<int, limited_allocator<int, static_cast<std::size_t>(-1)> >());
test(std::vector<int, limited_allocator<int, static_cast<std::size_t>(-1) / 2> >());
test(std::vector<int, limited_allocator<int, static_cast<std::size_t>(-1) / 4> >());
}

#endif // TEST_STD_VER >= 11

return true;
}

int main(int, char**) {
test();
tests();

#if TEST_STD_VER > 17
static_assert(test());
static_assert(tests());
#endif

return 0;
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