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!
!  atomic compare-and-swap routines for V9 (ultrasparc)
!
!  ======================================================================
!
!  Perform the sequence *a = b atomically with respect to previous value
!  of a (a0). If *a==a0 then assign *a to b, all in one atomic operation.
!  Returns 1 if assignment happened, and 0 otherwise.	
!
!  usage : old_val = compare_and_swap(address, oldval, newval)
!
!  -----------------------
!  Note on REGISTER USAGE:
!  as this is a LEAF procedure, a new stack frame is not created;
!  we use the caller stack frame so what would normally be %i (input)
!  registers are actually %o (output registers).  Also, we must not
!  overwrite the contents of %l (local) registers as they are not
!  assumed to be volatile during calls.
!
!  So, the registers used are:
!     %o0  [input]   - the address of the value to increment
!     %o1  [input]   - the old value to compare with	
!     %o2  [input]   - the new value to set for [%o0]
!     %o3  [local]   - work register
!  -----------------------
!  ======================================================================
!
!  v9

    .inline NativeCompareAndSwap,3

	stbar
	casx [%o0],%o1,%o2              ! compare *w with old value and set to new if equal
	cmp %o1,%o2                     ! did we succeed?
	be,a 1f                         ! yes
	mov 1,%o0                       ! return true (annulled when no jump)
	mov 0,%o0                       ! return false
1:

    .end

!
!  end
!
!  ======================================================================
!