[flang-commits] [flang] [llvm] [Flang] Introduce common::numeric_limits (PR #228108)

[Eugene Epshteyn via flang-commits]

================
@@ -304,5 +310,108 @@ using HostUnsignedIntType = typename HostUnsignedIntTypeHelper<BITS>::type;
 template <int BITS>
 using HostSignedIntType = typename HostSignedIntTypeHelper<BITS>::type;
 
+namespace detail {
+
+template <typename T> class numeric_limits_impl {
+public:
+  static constexpr bool is_specialized{false};
+};
+
+template <> class numeric_limits_impl<Fortran::common::UnsignedInt128> {
+public:
+  using T = Fortran::common::UnsignedInt128;
+
+  static constexpr bool is_specialized{true};
+  static constexpr bool is_signed{false};
+  static constexpr bool is_integer{true};
+
+  static constexpr T min() { return T{0, 0}; }
+  static constexpr T max() { return T{UINT64_MAX, UINT64_MAX}; }
+  static constexpr T lowest() { return min(); }
+};
+
+template <> class numeric_limits_impl<Fortran::common::SignedInt128> {
+public:
+  using T = Fortran::common::SignedInt128;
+
+  static constexpr bool is_specialized{true};
+  static constexpr bool is_signed{true};
+  static constexpr bool is_integer{true};
+
+  static constexpr T min() {
+    return T{static_cast<std::uint64_t>(INT64_MIN), 0};
+  }
+  static constexpr T max() {
+    return T{static_cast<std::uint64_t>(INT64_MAX), UINT64_MAX};
+  }
+  static constexpr T lowest() { return min(); }
+};
+
+#if defined(__SIZEOF_INT128__)
+// Handle discrepancy of support of bit 128 bit integers by compiler and
+// standard library. The compiler may treat __int128 as a builtin type, but the
+// standard library does not define std::numeric_limits for it. Two cases are
+// known:
+//
+// 1. clang-cl supports __int128, but MSVC, and therefore its STL used by
+//    clang-cl, does not.
+//
+// 2. Some versions of libstdc++ in strict mode (-std=c++NN)
+//    intentionally removes any use of __int128, even though gcc does not make
+//    such a distinction.
----------------
eugeneepshteyn wrote:

typos: "support of bit 128 bit integers" -> "support of 128-bit integers"; "Some versions of libstdc++ ... intentionally removes" -> "remove".

https://github.com/llvm/llvm-project/pull/228108