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115 lines
4.0 KiB
ArmAsm
115 lines
4.0 KiB
ArmAsm
!
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! The contents of this file are subject to the Netscape Public
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! License Version 1.1 (the "License"); you may not use this file
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! except in compliance with the License. You may obtain a copy of
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! the License at http://www.mozilla.org/NPL/
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!
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! Software distributed under the License is distributed on an "AS
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! IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
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! implied. See the License for the specific language governing
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! rights and limitations under the License.
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!
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! The Original Code is Mozilla Communicator client code, released
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! March 31, 1998.
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!
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! The Initial Developer of the Original Code is Netscape
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! Communications Corporation. Portions created by Netscape are
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! Copyright (C) 1998-1999 Netscape Communications Corporation. All
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! Rights Reserved.
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!
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! Contributor(s):
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!
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! Alternatively, the contents of this file may be used under the
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! terms of the GNU Public License (the "GPL"), in which case the
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! provisions of the GPL are applicable instead of those above.
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! If you wish to allow use of your version of this file only
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! under the terms of the GPL and not to allow others to use your
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! version of this file under the NPL, indicate your decision by
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! deleting the provisions above and replace them with the notice
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! and other provisions required by the GPL. If you do not delete
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! the provisions above, a recipient may use your version of this
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! file under either the NPL or the GPL.
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!
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!
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! atomic compare-and-swap routines for V8 sparc
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! and for V8+ (ultrasparc)
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!
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!
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! standard asm linkage macros; this module must be compiled
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! with the -P option (use C preprocessor)
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#include <sys/asm_linkage.h>
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! ======================================================================
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!
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! Perform the sequence *a = b atomically with respect to previous value
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! of a (a0). If *a==a0 then assign *a to b, all in one atomic operation.
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! Returns 1 if assignment happened, and 0 otherwise.
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!
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! usage : old_val = compare_and_swap(address, oldval, newval)
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!
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! -----------------------
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! Note on REGISTER USAGE:
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! as this is a LEAF procedure, a new stack frame is not created;
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! we use the caller stack frame so what would normally be %i (input)
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! registers are actually %o (output registers). Also, we must not
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! overwrite the contents of %l (local) registers as they are not
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! assumed to be volatile during calls.
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!
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! So, the registers used are:
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! %o0 [input] - the address of the value to increment
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! %o1 [input] - the old value to compare with
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! %o2 [input] - the new value to set for [%o0]
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! %o3 [local] - work register
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! -----------------------
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#ifndef ULTRA_SPARC
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! v8
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ENTRY(compare_and_swap) ! standard assembler/ELF prologue
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stbar
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mov -1,%o3 ! busy flag
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swap [%o0],%o3 ! get current value
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l1: cmp %o3,-1 ! busy?
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be,a l1 ! if so, spin
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swap [%o0],%o3 ! using branch-delay to swap back value
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cmp %o1,%o3 ! compare old with current
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be,a l2 ! if equal then swap in new value
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swap [%o0],%o2 ! done.
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swap [%o0],%o3 ! otherwise, swap back current value
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retl
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mov 0,%o0 ! return false
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l2: retl
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mov 1,%o0 ! return true
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SET_SIZE(compare_and_swap) ! standard assembler/ELF epilogue
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!
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! end
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!
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#else /* ULTRA_SPARC */
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! ======================================================================
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!
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! v9
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ENTRY(compare_and_swap) ! standard assembler/ELF prologue
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stbar
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cas [%o0],%o1,%o2 ! compare *w with old value and set to new if equal
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cmp %o1,%o2 ! did we succeed?
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be,a m1 ! yes
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mov 1,%o0 ! return true (annulled when no jump)
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mov 0,%o0 ! return false
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m1: retl
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nop
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SET_SIZE(compare_and_swap) ! standard assembler/ELF epilogue
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!
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! end
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!
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! ======================================================================
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!
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#endif
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