static inline int a_ll(volatile int *p) {
    int x;
    asm volatile ("lwarx %0, 0, %1" : "=r"(x) : "r"(p) : "memory");
    return x;
}

static inline int a_sc(volatile int *p, int x) {
    asm goto ("stwcx. %0, 0, %1\nbne- %l2" : : "r"(x), "r"(p) : "cc","memory" : fail);
    return 1;
fail:
    return 0;
}

int a_cas(volatile int *p, int t, int s) {
    int x;
    do {
        x = a_ll(p);
        if (x != t)
            break;
    } while (!a_sc(p, s));
    return x;
}