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

[Mark de Wever via cfe-commits]

================
@@ -0,0 +1,281 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 add_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 (-1, 0, 1)
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{0}, IntegerT{0});
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{0}, IntegerT{1});
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, IntegerT{0});
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{0}, IntegerT{-1});
+    assert(sum == IntegerT{-1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{-1}, IntegerT{0});
+    assert(sum == IntegerT{-1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, IntegerT{1});
+    assert(sum == IntegerT{2});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, IntegerT{-1});
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{-1}, IntegerT{1});
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{-1}, IntegerT{-1});
+    assert(sum == IntegerT{-2});
+  }
+
+  // No saturation (any value)
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{27}, IntegerT{28});
+    assert(sum == IntegerT{55});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{-27}, IntegerT{28});
+    assert(sum == IntegerT{1});
+  }
+
+  // No saturation (min, -1, 0, 1, max)
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, IntegerT{0});
+    assert(sum == minVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, IntegerT{1});
+    assert(sum == minVal + IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, IntegerT{0});
+    assert(sum == maxVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, IntegerT{-1});
+    assert(sum == maxVal + IntegerT{-1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, maxVal);
+    assert(sum == IntegerT{-1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, minVal);
+    assert(sum == IntegerT{-1});
+  }
+
+  // Saturation - max - both arguments positive
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, IntegerT{27});
+    assert(sum == maxVal);
+  }
+
+  {
+    // Large values
+    constexpr IntegerT x = maxVal / IntegerT{2} + IntegerT{27};
+    constexpr IntegerT y = maxVal / IntegerT{2} + IntegerT{28};
+
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(x, y);
+    assert(sum == maxVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, maxVal);
+    assert(sum == maxVal);
+  }
+
+  // Saturation - min - both arguments negative
+  {
+    // Large values
+    constexpr IntegerT x = minVal / IntegerT{2} + IntegerT{-27};
+    constexpr IntegerT y = minVal / IntegerT{2} + IntegerT{-28};
+
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(x, y);
+    assert(sum == minVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, minVal);
+    assert(sum == minVal);
+  }
+
+  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) sum = std::add_sat(IntegerT{0}, IntegerT{0});
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{0}, IntegerT{1});
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, IntegerT{0});
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, IntegerT{1});
+    assert(sum == IntegerT{2});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, IntegerT{0});
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, IntegerT{1});
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{0}, minVal);
+    assert(sum == IntegerT{0});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{1}, minVal);
+    assert(sum == IntegerT{1});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(IntegerT{27}, IntegerT{28});
+    assert(sum == IntegerT{55});
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, minVal);
+    assert(sum == minVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(minVal, maxVal);
+    assert(sum == maxVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, minVal);
+    assert(sum == maxVal);
+  }
+
+  // Saturation - max only
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, IntegerT{1});
+    assert(sum == maxVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, IntegerT{27});
+    assert(sum == maxVal);
+  }
+
+  {
+    // Large values
+    constexpr IntegerT x = maxVal / IntegerT{2} + IntegerT{27};
+    constexpr IntegerT y = maxVal / IntegerT{2} + IntegerT{28};
+
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(x, y);
+    assert(sum == maxVal);
+  }
+
+  {
+    std::same_as<IntegerT> decltype(auto) sum = std::add_sat(maxVal, maxVal);
+    assert(sum == maxVal);
+  }
+
+  return true;
+}
+
+constexpr bool test() {
+  // Signed
+  test_signed<signed char>();
+  test_signed<short int>();
+  test_signed<int>();
+  test_signed<long int>();
+  test_signed<long long int>();
+#ifndef _LIBCPP_HAS_NO_INT128
+  test_signed<__int128_t>();
+#endif
+  // Unsigned
+  test_unsigned<unsigned char>();
+  test_unsigned<unsigned short int>();
+  test_unsigned<unsigned int>();
+  test_unsigned<unsigned long int>();
+  test_unsigned<unsigned long long int>();
+#ifndef _LIBCPP_HAS_NO_INT128
+  test_unsigned<__uint128_t>();
+#endif
+
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
----------------
mordante wrote:

```suggestion
  test();
```
This is our generic test idom, let's keep that for consistency.

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