[libcxx-commits] [flang] [clang-tools-extra] [lld] [clang] [libcxx] [lldb] [compiler-rt] [mlir] [llvm] [libc++][numeric] P0543R3: Saturation arithmetic (PR #77967)

[Nikolas Klauser via libcxx-commits]

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@@ -0,0 +1,130 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++03, c++11, c++14, c++17, c++20, c++23
+
+// <numeric>
+
+// template<class T>
+// constexpr T div_sat(T x, T y) noexcept;                     // freestanding
+
+#include <cassert>
+#include <concepts>
+#include <limits>
+#include <numeric>
+
+#include "check_constexpr.h"
+
+template <typename IntegerT>
+constexpr bool test_signed() {
+  constexpr auto minVal = std::numeric_limits<IntegerT>::min();
+  constexpr auto maxVal = std::numeric_limits<IntegerT>::max();
+
+  static_assert(noexcept(std::div_sat(minVal, maxVal)));
+
+  // No saturation
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(IntegerT{3}, IntegerT{4});
+    assert(quot == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(maxVal, minVal);
+    assert(quot == (maxVal / minVal));
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(minVal, maxVal);
+    assert(quot == (minVal / maxVal));
+  }
+
+  // Saturation - max only
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(minVal, IntegerT{-1});
+    assert(quot == maxVal);
+  }
+
+  return true;
+}
+
+template <typename IntegerT>
+constexpr bool test_unsigned() {
+  constexpr auto minVal = std::numeric_limits<IntegerT>::min();
+  constexpr auto maxVal = std::numeric_limits<IntegerT>::max();
+
+  static_assert(noexcept(std::div_sat(minVal, maxVal)));
+
+  // No saturation
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(IntegerT{3}, IntegerT{4});
+    assert(quot == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(minVal, maxVal);
+    assert(quot == (minVal / maxVal));
+  }
+
+  // Unsigned integer devision never overflow
+
+  return true;
+}
+
+template <typename IntegerT>
+void test_constexpr() {
+  TEST_EXPRESSION_CONSTEXPR(std::div_sat(IntegerT{90}, IntegerT{84}));
+  TEST_EXPRESSION_NOT_CONSTEXPR(std::div_sat(IntegerT{90}, IntegerT{0}));
----------------
philnik777 wrote:

We don't want to test the compiler in our tests. There is no need to check that division by zero results in an expression that's not constant AFAICT. The check for the `constexpr` expression can simply be tested by putting it into a scope that is forced to be constant evaluated.

https://github.com/llvm/llvm-project/pull/77967