git: 9front

ref: 39ebda7c12e517c81acf582f4a7d1a288f888915
dir: /sys/src/cmd/unix/drawterm/posix-amd64/tas.c/

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

int
tas(long *x)
{
	int     v;

	__asm__(	"movl   $1, %%eax\n\t"
				"xchgl  %%eax,(%%rcx)"
				: "=a" (v)
				: "c" (x)
	);
	switch(v) {
	case 0:
	case 1:
		return v;
	default:
		print("canlock: corrupted 0x%lux\n", v);
		return 1;
	}
}