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*****
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2.0/LGPL
2.1
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,
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, released
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*****
40 ! atomic compare-and-swap routines for V8 sparc
41 ! and for V8+
(ultrasparc
)
44 ! standard asm linkage macros; this module must
be compiled
45 ! with the
-P option
(use C preprocessor
)
47 #include <sys/asm_linkage.h>
49 ! ======================================================================
51 ! Perform the sequence
*a = b atomically with respect to previous value
52 ! of
a (a0
). If *a==a0 then assign *a to b, all in one atomic operation.
53 ! Returns
1 if assignment happened
, and 0 otherwise.
55 ! usage
: old_val
= compare_and_swap
(address
, oldval
, newval
)
57 ! -----------------------
58 ! Note on REGISTER USAGE
:
59 ! as this is
a LEAF procedure
, a new stack frame is
not created;
60 ! we use the caller stack frame so what would normally
be %i
(input
)
61 ! registers are actually
%o
(output registers
). Also, we must not
62 ! overwrite the contents of
%l (local
) registers as they are
not
63 ! assumed to
be volatile during calls.
65 ! So
, the registers used are
:
66 ! %o0
[input
] - the address of the value to increment
67 ! %o1
[input
] - the old value to compare with
68 ! %o2
[input
] - the new value to set for
[%o0
]
69 ! %o3
[local
] - work register
70 ! -----------------------
74 ENTRY
(compare_and_swap
) ! standard assembler
/ELF prologue
77 mov
-1,%o3
! busy flag
78 swap
[%o0
],%o3
! get current value
79 l1
: cmp %o3
,-1 ! busy?
81 swap
[%o0
],%o3
! using branch-delay to swap back value
82 cmp %o1
,%o3
! compare old with current
83 be,a l2
! if equal then swap in new value
84 swap
[%o0
],%o2
! done.
85 swap
[%o0
],%o3
! otherwise
, swap back current value
87 mov
0,%o0
! return false
89 mov
1,%o0
! return true
91 SET_SIZE
(compare_and_swap
) ! standard assembler
/ELF epilogue
96 #else /* ULTRA_SPARC */
97 ! ======================================================================
101 ENTRY
(compare_and_swap
) ! standard assembler
/ELF prologue
104 cas
[%o0
],%o1
,%o2
! compare
*w with old value
and set to new if equal
105 cmp %o1
,%o2
! did we succeed?
107 mov
1,%o0
! return true
(annulled when no jump
)
108 mov
0,%o0
! return false
112 SET_SIZE
(compare_and_swap
) ! standard assembler
/ELF epilogue
117 ! ======================================================================