| 1 | #ifndef _COMPILER_H |
| 2 | #define _COMPILER_H |
| 3 | |
| 4 | /* |
| 5 | * compiler.h |
| 6 | * |
| 7 | * Compiler definitions. |
| 8 | * |
| 9 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> |
| 10 | * |
| 11 | * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED |
| 12 | * OR IMPLIED. ANY USE IS AT YOUR OWN RISK. |
| 13 | * |
| 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. |
| 19 | */ |
| 20 | |
| 21 | #define likely(x) __builtin_expect(!!(x), 1) |
| 22 | #define unlikely(x) __builtin_expect(!!(x), 0) |
| 23 | |
| 24 | #define barrier() asm volatile("" : : : "memory"); |
| 25 | |
| 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 | */ |
| 38 | #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&x) |
| 39 | |
| 40 | #endif /* _COMPILER_H */ |