OrionLibC

#include <sys/syscall.h>
#include <errno.h>

/* Check if fd refers to a terminal */
int
isatty(int fd)
{
	int ret;
	asm volatile("int $0x80" : "=a" (ret) : "0" (SYSCALL_ISATTY),
	             "c" (1), "S" (&fd));
	if (ret >= 0)
		return ret;
	errno = -ret;
	return 0;
}