[libc-commits] [libc] [libc] Fix definition of `UINT_MAX` in limits.h (PR #95279)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/95279

Summary:
Currently we use `(~0U)` for this definition, however the ~ operator
returns a different sign, meaning that preprocessor checks against this
value will fail. See https://godbolt.org/z/TrjaY1d8q where the
preprocessor thinks that it's not `0xffffffff` while the static
assertion thinks it is. This is because the latter does implicit
conversion but the preprocessor does not. This is now consistent with
other headers.


>From 3d3efaa7362cbe01ee8c4ed1bb823f8f29ef4d97 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Wed, 12 Jun 2024 12:48:29 -0500
Subject: [PATCH] [libc] Fix definition of `UINT_MAX` in limits.h

Summary:
Currently we use `(~0U)` for this definition, however the ~ operator
returns a different sign, meaning that preprocessor checks against this
value will fail. See https://godbolt.org/z/TrjaY1d8q where the
preprocessor thinks that it's not `0xffffffff` while the static
assertion thinks it is. This is because the latter does implicit
conversion but the preprocessor does not. This is now consistent with
other headers.
---
 libc/include/llvm-libc-macros/limits-macros.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libc/include/llvm-libc-macros/limits-macros.h b/libc/include/llvm-libc-macros/limits-macros.h
index 95f0f5f0baa58..3fab996b61ac9 100644
--- a/libc/include/llvm-libc-macros/limits-macros.h
+++ b/libc/include/llvm-libc-macros/limits-macros.h
@@ -148,7 +148,7 @@
 #endif // INT_MAX
 
 #ifndef UINT_MAX
-#define UINT_MAX (~0U)
+#define UINT_MAX (INT_MAX * 2U + 1U)
 #endif // UINT_MAX
 
 #ifndef LONG_MAX
@@ -160,7 +160,7 @@
 #endif // LONG_MAX
 
 #ifndef ULONG_MAX
-#define ULONG_MAX (~0UL)
+#define ULONG_MAX (LONG_MAX * 2UL + 1UL)
 #endif // ULONG_MAX
 
 #ifndef LLONG_MAX
@@ -172,7 +172,7 @@
 #endif // LLONG_MAX
 
 #ifndef ULLONG_MAX
-#define ULLONG_MAX (~0ULL)
+#define ULLONG_MAX (LLONG_MAX * 2ULL + 1ULL)
 #endif // ULLONG_MAX
 
 // *_MIN macros