ref: 8d93ccdbb2a2dee8d2eb1387da1b316fdf84b208
dir: /posix-arm64/cas.c/
#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) || (defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 7)))
return __atomic_compare_exchange_n(x, &old, new, 0, __ATOMIC_ACQ_REL, __ATOMIC_ACQUIRE);
#else
int v, t;
__asm__ (
"1: ldxr %0, [%3]\n"
" cmp %0, %4\n"
" bne 2f\n"
" stxr %w1, %5, [%3]\n"
" cmp %1, #0\n"
" bne 1b\n"
"2:"
: "=&r" (v), "=&r" (t)
: "m" (*x), "r" (x), "r" (old), "r" (new)
: "cc");
return (v == old);
#endif
}