Cleanup headers

[urcu.git] / urcu / compiler.h

diff --git a/urcu/compiler.h b/urcu/compiler.h
new file mode 100644 (file)
index 0000000..6f6d3e9
--- /dev/null
+++ b/urcu/compiler.h
@@ -0,0 +1,50 @@
+#ifndef _URCU_COMPILER_H
+#define _URCU_COMPILER_H
+
+/*
+ * compiler.h
+ *
+ * Compiler definitions.
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program
+ * for any purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is granted,
+ * provided the above notices are retained, and a notice that the code was
+ * modified is included with the above copyright notice.
+ */
+
+#define likely(x)      __builtin_expect(!!(x), 1)
+#define unlikely(x)    __builtin_expect(!!(x), 0)
+
+#define        barrier()       asm volatile("" : : : "memory");
+
+/*
+ * Instruct the compiler to perform only a single access to a variable
+ * (prohibits merging and refetching). The compiler is also forbidden to reorder
+ * successive instances of ACCESS_ONCE(), but only when the compiler is aware of
+ * particular ordering. Compiler ordering can be ensured, for example, by
+ * putting two ACCESS_ONCE() in separate C statements.
+ *
+ * This macro does absolutely -nothing- to prevent the CPU from reordering,
+ * merging, or refetching absolutely anything at any time.  Its main intended
+ * use is to mediate communication between process-level code and irq/NMI
+ * handlers, all running on the same CPU.
+ */
+#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&x)
+
+#if (__GNUC__ == 4)
+#define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
+#endif
+
+#ifdef __compiler_offsetof
+#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
+#else
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+#endif
+
+#endif /* _URCU_COMPILER_H */