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

[Mark de Wever via libcxx-commits]

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@@ -0,0 +1,267 @@
+//===----------------------------------------------------------------------===//
+//
+// 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>
+
+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{-1}, IntegerT{-1});
+    assert(quot == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(IntegerT{-1}, IntegerT{1});
+    assert(quot == IntegerT{-1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(IntegerT{-1}, minVal);
+    assert(quot == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(IntegerT{-1}, maxVal);
+    assert(quot == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) quot = std::div_sat(maxVal, IntegerT{-1});
+    assert(quot == IntegerT{-1} * maxVal);
+  }
----------------
mordante wrote:

why not `-maxVal`? 

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