[libc] Add support for cpp::make_signed

Author: gchatelet

libc/src/__support/CPP/type_traits.h

@@ -163,6 +163,25 @@ template <> struct make_unsigned<__uint128_t> : type_identity<__uint128_t> {};
 #endif
 template <typename T> using make_unsigned_t = typename make_unsigned<T>::type;
 
+template <typename T> struct make_signed;
+template <> struct make_signed<char> : type_identity<char> {};
+template <> struct make_signed<signed char> : type_identity<char> {};
+template <> struct make_signed<short> : type_identity<short> {};
+template <> struct make_signed<int> : type_identity<int> {};
+template <> struct make_signed<long> : type_identity<long> {};
+template <> struct make_signed<long long> : type_identity<long long> {};
+template <> struct make_signed<unsigned char> : type_identity<char> {};
+template <> struct make_signed<unsigned short> : type_identity<short> {};
+template <> struct make_signed<unsigned int> : type_identity<int> {};
+template <> struct make_signed<unsigned long> : type_identity<long> {};
+template <>
+struct make_signed<unsigned long long> : type_identity<long long> {};
+#ifdef __SIZEOF_INT128__
+template <> struct make_signed<__int128_t> : type_identity<__int128_t> {};
+template <> struct make_signed<__uint128_t> : type_identity<__int128_t> {};
+#endif
+template <typename T> using make_signed_t = typename make_signed<T>::type;
+
 // Compile time type selection.
 template <bool B, typename T, typename F>
 struct conditional : type_identity<T> {};

libc/src/__support/UInt.h

@@ -909,6 +909,24 @@ struct make_unsigned<Int<Bits>> : type_identity<UInt<Bits>> {
                 "Number of bits in Int should be a multiple of 64.");
 };
 
+template <size_t Bits>
+struct make_unsigned<UInt<Bits>> : type_identity<UInt<Bits>> {
+  static_assert(Bits > 0 && Bits % 64 == 0,
+                "Number of bits in Int should be a multiple of 64.");
+};
+
+template <size_t Bits>
+struct make_signed<Int<Bits>> : type_identity<Int<Bits>> {
+  static_assert(Bits > 0 && Bits % 64 == 0,
+                "Number of bits in Int should be a multiple of 64.");
+};
+
+template <size_t Bits>
+struct make_signed<UInt<Bits>> : type_identity<Int<Bits>> {
+  static_assert(Bits > 0 && Bits % 64 == 0,
+                "Number of bits in Int should be a multiple of 64.");
+};
+
 } // namespace __llvm_libc::cpp
 
 #endif // LLVM_LIBC_SRC_SUPPORT_UINT_H