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@ -1,6 +1,8 @@
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#ifndef _CAS_H
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#define _CAS_H
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#include <stddef.h>
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/* Atomic operations for lock-free data structures.
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* We operate on machine words and use size_t as a type.
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* CAS stands for Compare And Swap, the most common operation. */
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@ -11,6 +13,23 @@
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#define USE_BUILTINS
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#endif
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/* if (*x == oldval) { *x=newval; return 1; } else return 0; */
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static inline int compare_and_swap(volatile size_t* x,size_t oldval,size_t newval) {
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#ifdef USE_BUILTINS
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__sync_bool_compare_and_swap(x,oldval,newval);
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#elif defined(__i386__)
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char result;
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asm volatile ("lock; cmpxchgl %3, %0; setz %1" : "=m"(*x), "=q" (result) : "m" (*x), "r" (newval), "a" (oldval) : "memory");
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return result;
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#elif defined(__x86_64__)
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char result;
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asm volatile ("lock; cmpxchgq %3, %0; setz %1" : "=m"(*x), "=q" (result) : "m" (*x), "r" (newval), "a" (oldval) : "memory");
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return result;
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#else
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#error architecture not supported and gcc too old, edit CAS.h
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#endif
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}
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/* *x += val; */
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static inline void atomic_add(size_t* x,size_t val) {
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#ifdef USE_BUILTINS
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@ -95,23 +114,6 @@ static inline void atomic_and(volatile size_t* x,size_t val) {
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#endif
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}
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/* if (*x == oldval) { *x=newval; return 1; } else return 0; */
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static inline int compare_and_swap(volatile size_t* x,size_t oldval,size_t newval) {
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#ifdef USE_BUILTINS
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__sync_bool_compare_and_swap(x,oldval,newval);
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#elif defined(__i386__)
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char result;
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asm volatile ("lock; cmpxchgl %3, %0; setz %1" : "=m"(*x), "=q" (result) : "m" (*x), "r" (newval), "a" (oldval) : "memory");
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return result;
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#elif defined(__x86_64__)
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char result;
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asm volatile ("lock; cmpxchgq %3, %0; setz %1" : "=m"(*x), "=q" (result) : "m" (*x), "r" (newval), "a" (oldval) : "memory");
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return result;
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#else
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#error architecture not supported and gcc too old, edit CAS.h
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#endif
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}
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/* Optimization barrier */
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/* The "volatile" is due to gcc bugs */
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#define barrier() __asm__ __volatile__("": : :"memory")
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