Add std::midpoint for integral and poiner types. Described in P0811, reviewed as D59099.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356162 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.integer.pass.cpp

@@ -0,0 +1,137 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+// <numeric>
+
+// template <class _Tp>
+// _Tp midpoint(_Tp __a, _Tp __b) noexcept
+//
+
+#include <numeric>
+#include <cassert>
+#include "test_macros.h"
+
+template <typename T>
+void signed_test()
+{
+    constexpr T zero{0};
+    constexpr T one{1};
+    constexpr T two{2};
+    constexpr T three{3};
+    constexpr T four{4};
+
+    ASSERT_SAME_TYPE(decltype(std::midpoint(T(), T())), T);
+    ASSERT_NOEXCEPT(          std::midpoint(T(), T()));
+    using limits = std::numeric_limits<T>;
+    
+    static_assert(std::midpoint(one, three) == two, "");
+    static_assert(std::midpoint(three, one) == two, "");
+
+    assert(std::midpoint(zero, zero) == zero);
+    assert(std::midpoint(zero, two)  == one);
+    assert(std::midpoint(two, zero)  == one);
+    assert(std::midpoint(two, two)   == two);
+
+    assert(std::midpoint(one, four)    == two);
+    assert(std::midpoint(four, one)    == three);
+    assert(std::midpoint(three, four)  == three);
+    assert(std::midpoint(four, three)  == four);
+
+    assert(std::midpoint(T( 3), T( 4)) == T(3));
+    assert(std::midpoint(T( 4), T( 3)) == T(4));
+    assert(std::midpoint(T(-3), T( 4)) == T(0));
+    assert(std::midpoint(T(-4), T( 3)) == T(-1));
+    assert(std::midpoint(T( 3), T(-4)) == T(0));
+    assert(std::midpoint(T( 4), T(-3)) == T(1));
+    assert(std::midpoint(T(-3), T(-4)) == T(-3));
+    assert(std::midpoint(T(-4), T(-3)) == T(-4));
+    
+    static_assert(std::midpoint(limits::min(), limits::max()) == T(-1), "");
+    static_assert(std::midpoint(limits::max(), limits::min()) == T( 0), "");
+
+    static_assert(std::midpoint(limits::min(), T(6)) == limits::min()/2 + 3, "");
+    assert(       std::midpoint(T(6), limits::min()) == limits::min()/2 + 3);
+    assert(       std::midpoint(limits::max(), T(6)) == limits::max()/2 + 4);
+    static_assert(std::midpoint(T(6), limits::max()) == limits::max()/2 + 3, "");
+
+    assert(       std::midpoint(limits::min(), T(-6)) == limits::min()/2 - 3);
+    static_assert(std::midpoint(T(-6), limits::min()) == limits::min()/2 - 3, "");
+    static_assert(std::midpoint(limits::max(), T(-6)) == limits::max()/2 - 2, "");
+    assert(       std::midpoint(T(-6), limits::max()) == limits::max()/2 - 3);
+}
+
+template <typename T>
+void unsigned_test()
+{
+    constexpr T zero{0};
+    constexpr T one{1};
+    constexpr T two{2};
+    constexpr T three{3};
+    constexpr T four{4};
+
+    ASSERT_SAME_TYPE(decltype(std::midpoint(T(), T())), T);
+    ASSERT_NOEXCEPT(          std::midpoint(T(), T()));
+    using limits = std::numeric_limits<T>;
+    const T half_way = (limits::max() - limits::min())/2;
+    
+    static_assert(std::midpoint(one, three) == two, "");
+    static_assert(std::midpoint(three, one) == two, "");
+
+    assert(std::midpoint(zero, zero) == zero);
+    assert(std::midpoint(zero, two)  == one);
+    assert(std::midpoint(two, zero)  == one);
+    assert(std::midpoint(two, two)   == two);
+
+    assert(std::midpoint(one, four)    == two);
+    assert(std::midpoint(four, one)    == three);
+    assert(std::midpoint(three, four)  == three);
+    assert(std::midpoint(four, three)  == four);
+    
+    assert(std::midpoint(limits::min(), limits::max()) == T(half_way));
+    assert(std::midpoint(limits::max(), limits::min()) == T(half_way + 1));
+
+    static_assert(std::midpoint(limits::min(), T(6)) == limits::min()/2 + 3, "");
+    assert(       std::midpoint(T(6), limits::min()) == limits::min()/2 + 3);
+    assert(       std::midpoint(limits::max(), T(6)) == half_way + 4);
+    static_assert(std::midpoint(T(6), limits::max()) == half_way + 3, "");
+}
+
+
+int main(int, char**)
+{
+    signed_test<signed char>();
+    signed_test<short>();
+    signed_test<int>();
+    signed_test<long>();
+    signed_test<long long>();
+
+    signed_test<int8_t>();
+    signed_test<int16_t>();
+    signed_test<int32_t>();
+    signed_test<int64_t>();
+    signed_test<__int128_t>();
+
+    unsigned_test<unsigned char>();
+    unsigned_test<unsigned short>();
+    unsigned_test<unsigned int>();
+    unsigned_test<unsigned long>();
+    unsigned_test<unsigned long long>();
+
+    unsigned_test<uint8_t>();
+    unsigned_test<uint16_t>();
+    unsigned_test<uint32_t>();
+    unsigned_test<uint64_t>();
+    unsigned_test<__uint128_t>();
+
+//     int_test<char>();
+    signed_test<ptrdiff_t>();
+    unsigned_test<size_t>();
+
+    return 0;
+}