32-bit ucas on amd64

[Paul Irofti]

I need this for acpi locking, okay?

(I'd also like to get rid of the silly x86_* prefix to match the i386
function name, but that's a different topic)

Index: arch/amd64/include/atomic.h
===================================================================
RCS file: /cvs/src/sys/arch/amd64/include/atomic.h,v
retrieving revision 1.8
diff -u -p -r1.8 atomic.h
--- arch/amd64/include/atomic.h 23 Mar 2011 16:54:34 -0000      1.8
+++ arch/amd64/include/atomic.h 19 Sep 2012 12:38:31 -0000
@@ -90,6 +90,17 @@ x86_atomic_clearbits_u32(volatile u_int3
        __asm __volatile(LOCK " andl %1,%0" :  "=m" (*ptr) : "ir" (~bits));
 }
 
+static __inline int
+x86_atomic_ucas_32(volatile uint32_t *ptr, uint32_t expect, uint32_t set)
+{
+       u_long res;
+
+       __asm volatile(LOCK " cmpxchgl %2, %1" : "=a" (res), "=m" (*ptr)
+           : "r" (set), "a" (expect), "m" (*ptr) : "memory");
+
+       return (res);
+}
+
 static __inline u_long
 x86_atomic_cas_ul(volatile u_long *ptr, u_long expect, u_long set)
 {