#include <sys/types.h>
typedef u_int64_t pt_entry_t;

/*
 * CMPXHCH8B
 * This is a larger and more unwieldy version of CMPXCHG: it compares
 * the 64-bit (eight-byte) value stored at [mem] with the value in EDX:EAX.
 * If they are equal, it sets the zero flag and stores ECX:EBX into the
 * memory area. If they are unequal, it clears the zero flag and leaves
 * the memory area untouched.
 */
static __inline pt_entry_t
__pmap_pte_set(pt_entry_t *ptep, u_int32_t newlo, u_int32_t newhi)
{
	register u_int64_t old;

	__asm __volatile(
	    "1: movl (%1), %%eax\n\t"
	    "movl 4(%1), %%edx\n\t"
	    "cmpxchg8b (%1)\n\t"
	    "jnz 1b"
	    : "=A,A"(old) : "D,S"(ptep), "b,b"(newlo), "c,c"(newhi) : "memory");
	return old;
}

static __inline pt_entry_t
__pmap_pte_set_constant(pt_entry_t *ptep, pt_entry_t newval)
{

	return __pmap_pte_set(ptep, newval, newval >> 32);
}

static __inline pt_entry_t
__pmap_pte_set_variable(pt_entry_t *ptep,  pt_entry_t newval)
{

	return __pmap_pte_set(ptep, ((u_int32_t *)&newval)[0],
	    ((u_int32_t *)&newval)[1]);
}
static __inline pt_entry_t
pmap_pte_set(pt_entry_t *ptep, pt_entry_t newval)
{

	return __builtin_constant_p(newval) ?
	    __pmap_pte_set_constant(ptep, newval) :
	    __pmap_pte_set_variable(ptep, newval);
}

/* tests */
pt_entry_t pte[512];

/* test case for a variable set */
int
foo(pt_entry_t new)
{
	register int bar __asm("edi");
	pmap_pte_set(&pte[2], new);
	return bar;
}

/* test case for a constant set */
void
bar(void)
{
	pmap_pte_set(&pte[1], 10);
}