[libc-commits] [libc] [libc] Clean up cpp::numeric_limits (PR #177461)

[via libc-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Roland McGrath (frobtech)

<details>
<summary>Changes</summary>

This adds the missing is_signed member and uses a generic
implementation for all integral types, using the same methods
employed by the libc++ implementation.


---
Full diff: https://github.com/llvm/llvm-project/pull/177461.diff


1 Files Affected:

- (modified) libc/src/__support/CPP/limits.h (+17-61) 


``````````diff
diff --git a/libc/src/__support/CPP/limits.h b/libc/src/__support/CPP/limits.h
index cf4beb9cc859f..d35141be8c749 100644
--- a/libc/src/__support/CPP/limits.h
+++ b/libc/src/__support/CPP/limits.h
@@ -1,4 +1,4 @@
-//===-- A self contained equivalent of std::limits --------------*- C++ -*-===//
+//===-- A self contained equivalent of <limits> ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -13,78 +13,34 @@
 #include "src/__support/CPP/type_traits/is_integral.h"
 #include "src/__support/CPP/type_traits/is_signed.h"
 #include "src/__support/macros/attributes.h" // LIBC_INLINE
-#include "src/__support/macros/config.h"
-#include "src/__support/macros/properties/types.h" // LIBC_TYPES_HAS_INT128
 
 namespace LIBC_NAMESPACE_DECL {
 namespace cpp {
 
 namespace internal {
 
-template <typename T, T min_value, T max_value> struct integer_impl {
-  static_assert(cpp::is_integral_v<T>);
-  LIBC_INLINE static constexpr T max() { return max_value; }
-  LIBC_INLINE static constexpr T min() { return min_value; }
-  LIBC_INLINE_VAR static constexpr int digits =
-      CHAR_BIT * sizeof(T) - cpp::is_signed_v<T>;
-};
-
-} // namespace internal
-
-template <class T> struct numeric_limits {};
-
-// TODO: Add numeric_limits specializations as needed for new types.
-template <>
-struct numeric_limits<short>
-    : public internal::integer_impl<short, SHRT_MIN, SHRT_MAX> {};
-
-template <>
-struct numeric_limits<unsigned short>
-    : public internal::integer_impl<unsigned short, 0, USHRT_MAX> {};
+template <typename T, bool is_integral> struct numeric_limits_impl {};
 
-template <>
-struct numeric_limits<int>
-    : public internal::integer_impl<int, INT_MIN, INT_MAX> {};
+template <typename T> struct numeric_limits_impl<T, true> {
+  LIBC_INLINE_VAR static constexpr bool is_signed = T(-1) < T(0);
 
-template <>
-struct numeric_limits<unsigned int>
-    : public internal::integer_impl<unsigned int, 0, UINT_MAX> {};
-
-template <>
-struct numeric_limits<long>
-    : public internal::integer_impl<long, LONG_MIN, LONG_MAX> {};
-
-template <>
-struct numeric_limits<unsigned long>
-    : public internal::integer_impl<unsigned long, 0, ULONG_MAX> {};
-
-template <>
-struct numeric_limits<long long>
-    : public internal::integer_impl<long long, LLONG_MIN, LLONG_MAX> {};
-
-template <>
-struct numeric_limits<unsigned long long>
-    : public internal::integer_impl<unsigned long long, 0, ULLONG_MAX> {};
+  LIBC_INLINE_VAR static constexpr int digits =
+      (CHAR_BIT * sizeof(T)) - cpp::is_signed_v<T>;
 
-template <>
-struct numeric_limits<char>
-    : public internal::integer_impl<char, CHAR_MIN, CHAR_MAX> {};
+  LIBC_INLINE static constexpr T min() {
+    return is_signed ? T(T(1) << digits) : 0;
+  }
 
-template <>
-struct numeric_limits<signed char>
-    : public internal::integer_impl<signed char, SCHAR_MIN, SCHAR_MAX> {};
+  LIBC_INLINE static constexpr T max() {
+    return is_signed ? T(T(~0) ^ min()) : T(~0);
+  }
+};
 
-template <>
-struct numeric_limits<unsigned char>
-    : public internal::integer_impl<unsigned char, 0, UCHAR_MAX> {};
+} // namespace internal
 
-#ifdef LIBC_TYPES_HAS_INT128
-// On platform where UInt128 resolves to __uint128_t, this specialization
-// provides the limits of UInt128.
-template <>
-struct numeric_limits<__uint128_t>
-    : public internal::integer_impl<__uint128_t, 0, ~__uint128_t(0)> {};
-#endif
+template <typename T>
+struct numeric_limits
+    : public internal::numeric_limits_impl<T, is_integral_v<T>> {};
 
 } // namespace cpp
 } // namespace LIBC_NAMESPACE_DECL

``````````

</details>


https://github.com/llvm/llvm-project/pull/177461