shithub: drawcpu

ref: 82dc85253c9ab0f7b9925c69e4b065ca4347ab04
dir: /posix-sun4u/cas.c/

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#include "u.h"
#include "libc.h"

#ifndef __has_builtin
#define __has_builtin(x) 0
#endif

int
cas(int *x, int old, int new)
{
#if __has_builtin(__atomic_compare_exchange_n)
    return __atomic_compare_exchange_n(x, &old, new, 0, __ATOMIC_ACQ_REL, __ATOMIC_ACQUIRE);
#else
    int result;
    __asm__ __volatile__(
        "casa [%2] %%asi, %3, %1\n"
        "cmp %3, %1\n"
        "mov %4, %0\n"
        "movne %4, 0, %0"
        : "=&r" (result), "+r" (new), "+m" (*x)
        : "r" (x), "r" (old)
        : "cc");
    return result;
#endif
}