From 096df4242a1062904369a417449c1d12fe40f507 Mon Sep 17 00:00:00 2001
From: Naman Dixit <code@namandixit.net>
Date: Sat, 6 Jun 2020 15:11:09 +0530
Subject: [PATCH] Proper cross-platform thread_local and alignas

---
 settings.h | 74 ++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 64 insertions(+), 10 deletions(-)

diff --git a/settings.h b/settings.h
index 695ebfb7..3bb77264 100644
--- a/settings.h
+++ b/settings.h
@@ -10,20 +10,74 @@
    do not use this unless you are certain your application won't use SSE */
 /* #define LIBCO_NO_SSE */
 
-#if defined(LIBCO_C)
-  #if defined(LIBCO_MP)
-    #define thread_local __thread
-  #else
+#if !defined(thread_local) // User can override thread_local for obscure compilers
+  #if !defined(LIBCO_MP) // Running in single-threaded environment
     #define thread_local
+  #else // Running in multi-threaded environment
+    #if defined(__STDC_VERSION__) // Compiling as C Language
+      #if defined(_MSC_VER) // Don't rely on MSVC's C11 support
+        #define thread_local __declspec(thread)
+      #elif __STDC_VERSION__ < 201112L // If we are on C90/99
+        #if defined(__clang__) || defined(__GNUC__) // Clang and GCC
+          #define thread_local __thread
+        #else // Otherwise, we ignore the directive (unless user provides their own)
+          #define thread_local
+        #endif
+      #else // C11 and newer define thread_local in threads.h
+        #include <threads.h>
+      #endif
+    #elif defined(__cplusplus) // Compiling as C++ Language
+      #if __cplusplus < 201103L // thread_local is a C++11 feature
+        #if defined(_MSC_VER)
+          #define thread_local __declspec(thread)
+        #elif defined(__clang__) || defined(__GNUC__)
+          #define thread_local __thread
+        #else // Otherwise, we ignore the directive (unless user provides their own)
+          #define thread_local
+        #endif
+      #else // In C++ >= 11, thread_local in a builtin keyword
+        // Don't do anything
+      #endif
+    #endif
   #endif
 #endif
 
-#if __STDC_VERSION__ >= 201112L
-  #if !defined(_MSC_VER)
-    #include <stdalign.h>
-  #endif
-#else
-  #define alignas(bytes)
+/* In alignas(a), 'a' should be a power of two that is at least the type's
+   alignment and at most the implementation's alignment limit.  This limit is
+   2**13 on MSVC. To be portable to MSVC through at least version 10.0,
+   'a' should be an integer constant, as MSVC does not support expressions
+   such as 1 << 3.
+
+   The following C11 requirements are NOT supported on MSVC:
+
+   - If 'a' is zero, alignas has no effect.
+   - alignas can be used multiple times; the strictest one wins.
+   - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
+*/
+#if !defined(alignas) 
+  #if defined(__STDC_VERSION__) // C Language
+    #if defined(_MSC_VER) // Don't rely on MSVC's C11 support
+      #define alignas(bytes) __declspec(align(bytes))
+    #elif __STDC_VERSION__ >= 201112L // C11 and above
+      #include <stdalign.h>
+    #elif defined(__clang__) || defined(__GNUC__) // C90/99 on Clang/GCC
+      #define alignas(bytes) __attribute__ ((aligned (bytes)))
+    #else // Otherwise, we ignore the directive (user should provide their own)
+      #define alignas(bytes)
+    #endif
+  #elif defined(__cplusplus) // C++ Language
+    #if __cplusplus < 201103L
+      #if defined(_MSC_VER)
+        #define alignas(bytes) __declspec(align(bytes))
+      #elif defined(__clang__) || defined(__GNUC__) // C++98/03 on Clang/GCC
+        #define alignas(bytes) __attribute__ ((aligned (bytes)))
+      #else // Otherwise, we ignore the directive (unless user provides their own)
+        #define alignas(bytes)
+      #endif
+    #else // C++ >= 11 has alignas keyword
+      // Do nothing
+    #endif
+  #endif // = !defined(__STDC_VERSION__) && !defined(__cplusplus)
 #endif
 
 #if !defined(LIBCO_ASSERT)