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[urcu.git] / urcu / compiler.h
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1#ifndef _URCU_COMPILER_H
2#define _URCU_COMPILER_H
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3
4/*
5 * compiler.h
6 *
7 * Compiler definitions.
8 *
9 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
10 *
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11 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
12 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
af02d47e 13 *
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14 * Permission is hereby granted to use or copy this program
15 * for any purpose, provided the above notices are retained on all copies.
16 * Permission to modify the code and to distribute modified code is granted,
17 * provided the above notices are retained, and a notice that the code was
18 * modified is included with the above copyright notice.
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19 */
20
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21#define likely(x) __builtin_expect(!!(x), 1)
22#define unlikely(x) __builtin_expect(!!(x), 0)
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23
24#define barrier() asm volatile("" : : : "memory");
25
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26/*
27 * Instruct the compiler to perform only a single access to a variable
28 * (prohibits merging and refetching). The compiler is also forbidden to reorder
29 * successive instances of ACCESS_ONCE(), but only when the compiler is aware of
30 * particular ordering. Compiler ordering can be ensured, for example, by
31 * putting two ACCESS_ONCE() in separate C statements.
32 *
33 * This macro does absolutely -nothing- to prevent the CPU from reordering,
34 * merging, or refetching absolutely anything at any time. Its main intended
35 * use is to mediate communication between process-level code and irq/NMI
36 * handlers, all running on the same CPU.
37 */
2dc5fa0f 38#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&x)
af02d47e 39
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40#if (__GNUC__ == 4)
41#define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
42#endif
43
44#ifdef __compiler_offsetof
45#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
46#else
47#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
48#endif
49
ec4e58a3 50#endif /* _URCU_COMPILER_H */
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