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Use STL algorithms available since C++14 to implement absl::equal and

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absl::rotate.

Prior to C++14 these were either polyfills or fixes for bugs in
standard libraries.

PiperOrigin-RevId: 575295101
Change-Id: Ie01e77fedadc879c73203d71babd40c87a419af3
This commit is contained in:
Derek Mauro
2023-10-20 12:49:11 -07:00
committed by Copybara-Service
parent 133360ca44
commit b5fb0582b5
4 changed files with 8 additions and 384 deletions
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14
absl/algorithm/BUILD.bazel
View File

@@ -56,20 +56,6 @@ cc_test(
],
)
cc_binary(
name = "algorithm_benchmark",
testonly = 1,
srcs = ["equal_benchmark.cc"],
copts = ABSL_TEST_COPTS,
linkopts = ABSL_DEFAULT_LINKOPTS,
tags = ["benchmark"],
deps = [
":algorithm",
"//absl/base:core_headers",
"@com_github_google_benchmark//:benchmark_main",
],
)
cc_library(
name = "container",
hdrs = [

111
absl/algorithm/algorithm.h
View File

@@ -31,92 +31,17 @@
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace algorithm_internal {
// Performs comparisons with operator==, similar to C++14's `std::equal_to<>`.
struct EqualTo {
template <typename T, typename U>
bool operator()(const T& a, const U& b) const {
return a == b;
}
};
template <typename InputIter1, typename InputIter2, typename Pred>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred pred, std::input_iterator_tag,
std::input_iterator_tag) {
while (true) {
if (first1 == last1) return first2 == last2;
if (first2 == last2) return false;
if (!pred(*first1, *first2)) return false;
++first1;
++first2;
}
}
template <typename InputIter1, typename InputIter2, typename Pred>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred&& pred, std::random_access_iterator_tag,
std::random_access_iterator_tag) {
return (last1 - first1 == last2 - first2) &&
std::equal(first1, last1, first2, std::forward<Pred>(pred));
}
// When we are using our own internal predicate that just applies operator==, we
// forward to the non-predicate form of std::equal. This enables an optimization
// in libstdc++ that can result in std::memcmp being used for integer types.
template <typename InputIter1, typename InputIter2>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, algorithm_internal::EqualTo /* unused */,
std::random_access_iterator_tag,
std::random_access_iterator_tag) {
return (last1 - first1 == last2 - first2) &&
std::equal(first1, last1, first2);
}
template <typename It>
It RotateImpl(It first, It middle, It last, std::true_type) {
return std::rotate(first, middle, last);
}
template <typename It>
It RotateImpl(It first, It middle, It last, std::false_type) {
std::rotate(first, middle, last);
return std::next(first, std::distance(middle, last));
}
} // namespace algorithm_internal
// equal()
// rotate()
//
// Compares the equality of two ranges specified by pairs of iterators, using
// the given predicate, returning true iff for each corresponding iterator i1
// and i2 in the first and second range respectively, pred(*i1, *i2) == true
// Historical note: Abseil once provided implementations of these algorithms
// prior to their adoption in C++14. New code should prefer to use the std
// variants.
//
// This comparison takes at most min(`last1` - `first1`, `last2` - `first2`)
// invocations of the predicate. Additionally, if InputIter1 and InputIter2 are
// both random-access iterators, and `last1` - `first1` != `last2` - `first2`,
// then the predicate is never invoked and the function returns false.
//
// This is a C++11-compatible implementation of C++14 `std::equal`. See
// https://en.cppreference.com/w/cpp/algorithm/equal for more information.
template <typename InputIter1, typename InputIter2, typename Pred>
bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred&& pred) {
return algorithm_internal::EqualImpl(
first1, last1, first2, last2, std::forward<Pred>(pred),
typename std::iterator_traits<InputIter1>::iterator_category{},
typename std::iterator_traits<InputIter2>::iterator_category{});
}
// Overload of equal() that performs comparison of two ranges specified by pairs
// of iterators using operator==.
template <typename InputIter1, typename InputIter2>
bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2) {
return absl::equal(first1, last1, first2, last2,
algorithm_internal::EqualTo{});
}
// See the documentation for the STL <algorithm> header for more information:
// https://en.cppreference.com/w/cpp/header/algorithm
using std::equal;
using std::rotate;
// linear_search()
//
@@ -133,26 +58,6 @@ bool linear_search(InputIterator first, InputIterator last,
return std::find(first, last, value) != last;
}
// rotate()
//
// Performs a left rotation on a range of elements (`first`, `last`) such that
// `middle` is now the first element. `rotate()` returns an iterator pointing to
// the first element before rotation. This function is exactly the same as
// `std::rotate`, but fixes a bug in gcc
// <= 4.9 where `std::rotate` returns `void` instead of an iterator.
//
// The complexity of this algorithm is the same as that of `std::rotate`, but if
// `ForwardIterator` is not a random-access iterator, then `absl::rotate`
// performs an additional pass over the range to construct the return value.
template <typename ForwardIterator>
ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last) {
return algorithm_internal::RotateImpl(
first, middle, last,
std::is_same<decltype(std::rotate(first, middle, last)),
ForwardIterator>());
}
ABSL_NAMESPACE_END
} // namespace absl

141
absl/algorithm/algorithm_test.cc
View File

@@ -24,137 +24,6 @@
namespace {
TEST(EqualTest, DefaultComparisonRandomAccess) {
std::vector<int> v1{1, 2, 3};
std::vector<int> v2 = v1;
std::vector<int> v3 = {1, 2};
std::vector<int> v4 = {1, 2, 4};
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v3.begin(), v3.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v4.begin(), v4.end()));
}
TEST(EqualTest, DefaultComparison) {
std::list<int> lst1{1, 2, 3};
std::list<int> lst2 = lst1;
std::list<int> lst3{1, 2};
std::list<int> lst4{1, 2, 4};
EXPECT_TRUE(absl::equal(lst1.begin(), lst1.end(), lst2.begin(), lst2.end()));
EXPECT_FALSE(absl::equal(lst1.begin(), lst1.end(), lst3.begin(), lst3.end()));
EXPECT_FALSE(absl::equal(lst1.begin(), lst1.end(), lst4.begin(), lst4.end()));
}
TEST(EqualTest, EmptyRange) {
std::vector<int> v1{1, 2, 3};
std::vector<int> empty1;
std::vector<int> empty2;
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105705
#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wnonnull"
#endif
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), empty1.begin(), empty1.end()));
#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
#pragma GCC diagnostic pop
#endif
EXPECT_FALSE(absl::equal(empty1.begin(), empty1.end(), v1.begin(), v1.end()));
EXPECT_TRUE(
absl::equal(empty1.begin(), empty1.end(), empty2.begin(), empty2.end()));
}
TEST(EqualTest, MixedIterTypes) {
std::vector<int> v1{1, 2, 3};
std::list<int> lst1{v1.begin(), v1.end()};
std::list<int> lst2{1, 2, 4};
std::list<int> lst3{1, 2};
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), lst1.begin(), lst1.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), lst2.begin(), lst2.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), lst3.begin(), lst3.end()));
}
TEST(EqualTest, MixedValueTypes) {
std::vector<int> v1{1, 2, 3};
std::vector<char> v2{1, 2, 3};
std::vector<char> v3{1, 2};
std::vector<char> v4{1, 2, 4};
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v3.begin(), v3.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v4.begin(), v4.end()));
}
TEST(EqualTest, WeirdIterators) {
std::vector<bool> v1{true, false};
std::vector<bool> v2 = v1;
std::vector<bool> v3{true};
std::vector<bool> v4{true, true, true};
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v3.begin(), v3.end()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v4.begin(), v4.end()));
}
TEST(EqualTest, CustomComparison) {
int n[] = {1, 2, 3, 4};
std::vector<int*> v1{&n[0], &n[1], &n[2]};
std::vector<int*> v2 = v1;
std::vector<int*> v3{&n[0], &n[1], &n[3]};
std::vector<int*> v4{&n[0], &n[1]};
auto eq = [](int* a, int* b) { return *a == *b; };
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end(), eq));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v3.begin(), v3.end(), eq));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v4.begin(), v4.end(), eq));
}
TEST(EqualTest, MoveOnlyPredicate) {
std::vector<int> v1{1, 2, 3};
std::vector<int> v2{4, 5, 6};
// move-only equality predicate
struct Eq {
Eq() = default;
Eq(Eq &&) = default;
Eq(const Eq &) = delete;
Eq &operator=(const Eq &) = delete;
bool operator()(const int a, const int b) const { return a == b; }
};
EXPECT_TRUE(absl::equal(v1.begin(), v1.end(), v1.begin(), v1.end(), Eq()));
EXPECT_FALSE(absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end(), Eq()));
}
struct CountingTrivialPred {
int* count;
bool operator()(int, int) const {
++*count;
return true;
}
};
TEST(EqualTest, RandomAccessComplexity) {
std::vector<int> v1{1, 1, 3};
std::vector<int> v2 = v1;
std::vector<int> v3{1, 2};
do {
int count = 0;
absl::equal(v1.begin(), v1.end(), v2.begin(), v2.end(),
CountingTrivialPred{&count});
EXPECT_LE(count, 3);
} while (std::next_permutation(v2.begin(), v2.end()));
int count = 0;
absl::equal(v1.begin(), v1.end(), v3.begin(), v3.end(),
CountingTrivialPred{&count});
EXPECT_EQ(count, 0);
}
class LinearSearchTest : public testing::Test {
protected:
LinearSearchTest() : container_{1, 2, 3} {}
@@ -178,14 +47,4 @@ TEST_F(LinearSearchTest, linear_searchConst) {
absl::linear_search(const_container->begin(), const_container->end(), 4));
}
TEST(RotateTest, Rotate) {
std::vector<int> v{0, 1, 2, 3, 4};
EXPECT_EQ(*absl::rotate(v.begin(), v.begin() + 2, v.end()), 0);
EXPECT_THAT(v, testing::ElementsAreArray({2, 3, 4, 0, 1}));
std::list<int> l{0, 1, 2, 3, 4};
EXPECT_EQ(*absl::rotate(l.begin(), std::next(l.begin(), 3), l.end()), 0);
EXPECT_THAT(l, testing::ElementsAreArray({3, 4, 0, 1, 2}));
}
} // namespace

126
absl/algorithm/equal_benchmark.cc
View File

@@ -1,126 +0,0 @@
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include <cstdint>
#include <cstring>
#include "absl/algorithm/algorithm.h"
#include "benchmark/benchmark.h"
namespace {
// The range of sequence sizes to benchmark.
constexpr int kMinBenchmarkSize = 1024;
constexpr int kMaxBenchmarkSize = 8 * 1024 * 1024;
// A user-defined type for use in equality benchmarks. Note that we expect
// std::memcmp to win for this type: libstdc++'s std::equal only defers to
// memcmp for integral types. This is because it is not straightforward to
// guarantee that std::memcmp would produce a result "as-if" compared by
// operator== for other types (example gotchas: NaN floats, structs with
// padding).
struct EightBits {
explicit EightBits(int /* unused */) : data(0) {}
bool operator==(const EightBits& rhs) const { return data == rhs.data; }
uint8_t data;
};
template <typename T>
void BM_absl_equal_benchmark(benchmark::State& state) {
std::vector<T> xs(state.range(0), T(0));
std::vector<T> ys = xs;
while (state.KeepRunning()) {
const bool same = absl::equal(xs.begin(), xs.end(), ys.begin(), ys.end());
benchmark::DoNotOptimize(same);
}
}
template <typename T>
void BM_std_equal_benchmark(benchmark::State& state) {
std::vector<T> xs(state.range(0), T(0));
std::vector<T> ys = xs;
while (state.KeepRunning()) {
const bool same = std::equal(xs.begin(), xs.end(), ys.begin());
benchmark::DoNotOptimize(same);
}
}
template <typename T>
void BM_memcmp_benchmark(benchmark::State& state) {
std::vector<T> xs(state.range(0), T(0));
std::vector<T> ys = xs;
while (state.KeepRunning()) {
const bool same =
std::memcmp(xs.data(), ys.data(), xs.size() * sizeof(T)) == 0;
benchmark::DoNotOptimize(same);
}
}
// The expectation is that the compiler should be able to elide the equality
// comparison altogether for sufficiently simple types.
template <typename T>
void BM_absl_equal_self_benchmark(benchmark::State& state) {
std::vector<T> xs(state.range(0), T(0));
while (state.KeepRunning()) {
const bool same = absl::equal(xs.begin(), xs.end(), xs.begin(), xs.end());
benchmark::DoNotOptimize(same);
}
}
BENCHMARK_TEMPLATE(BM_absl_equal_benchmark, uint8_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_std_equal_benchmark, uint8_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_memcmp_benchmark, uint8_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_self_benchmark, uint8_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_benchmark, uint16_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_std_equal_benchmark, uint16_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_memcmp_benchmark, uint16_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_self_benchmark, uint16_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_benchmark, uint32_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_std_equal_benchmark, uint32_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_memcmp_benchmark, uint32_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_self_benchmark, uint32_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_benchmark, uint64_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_std_equal_benchmark, uint64_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_memcmp_benchmark, uint64_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_self_benchmark, uint64_t)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_benchmark, EightBits)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_std_equal_benchmark, EightBits)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_memcmp_benchmark, EightBits)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
BENCHMARK_TEMPLATE(BM_absl_equal_self_benchmark, EightBits)
->Range(kMinBenchmarkSize, kMaxBenchmarkSize);
} // namespace