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!
! The contents of this file are subject to the Netscape Public
! License Version 1.1 (the "License"); you may not use this file
! except in compliance with the License. You may obtain a copy of
! the License at http://www.mozilla.org/NPL/
!
! Software distributed under the License is distributed on an "AS
! IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
! implied. See the License for the specific language governing
! rights and limitations under the License.
!
! The Original Code is Mozilla Communicator client code, released
! March 31, 1998.
!
! The Initial Developer of the Original Code is Netscape
! Communications Corporation. Portions created by Netscape are
! Copyright (C) 1998-1999 Netscape Communications Corporation. All
! Rights Reserved.
!
! Contributor(s):
!
! Alternatively, the contents of this file may be used under the
! terms of the GNU Public License (the "GPL"), in which case the
! provisions of the GPL are applicable instead of those above.
! If you wish to allow use of your version of this file only
! under the terms of the GPL and not to allow others to use your
! version of this file under the NPL, indicate your decision by
! deleting the provisions above and replace them with the notice
! and other provisions required by the GPL. If you do not delete
! the provisions above, a recipient may use your version of this
! file under either the NPL or the GPL.
!
!
! atomic compare-and-swap routines for V8 sparc
! and for V8+ (ultrasparc)
!
!
! standard asm linkage macros; this module must be compiled
! with the -P option (use C preprocessor)
#include <sys/asm_linkage.h>
! ======================================================================
!
! 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
! -----------------------
#ifndef ULTRA_SPARC
! v8
ENTRY(compare_and_swap) ! standard assembler/ELF prologue
stbar
mov -1,%o3 ! busy flag
swap [%o0],%o3 ! get current value
l1: cmp %o3,-1 ! busy?
be,a l1 ! if so, spin
swap [%o0],%o3 ! using branch-delay to swap back value
cmp %o1,%o3 ! compare old with current
be,a l2 ! if equal then swap in new value
swap [%o0],%o2 ! done.
swap [%o0],%o3 ! otherwise, swap back current value
retl
mov 0,%o0 ! return false
l2: retl
mov 1,%o0 ! return true
SET_SIZE(compare_and_swap) ! standard assembler/ELF epilogue
!
! end
!
#else /* ULTRA_SPARC */
! ======================================================================
!
! v9
ENTRY(compare_and_swap) ! standard assembler/ELF prologue
stbar
cas [%o0],%o1,%o2 ! compare *w with old value and set to new if equal
cmp %o1,%o2 ! did we succeed?
be,a m1 ! yes
mov 1,%o0 ! return true (annulled when no jump)
mov 0,%o0 ! return false
m1: retl
nop
SET_SIZE(compare_and_swap) ! standard assembler/ELF epilogue
!
! end
!
! ======================================================================
!
#endif
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