src/sparc/atomic.s

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!
! atomic-sparc.s
!
! $Id$
!
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!
! Copyright 2005-2006 The Apache Software Foundation or its licensors,
! as applicable.
!
! Copyright 2002-2006 Rogue Wave Software.
!
! Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
!
! Unless required by applicable law or agreed to in writing, software
! distributed under the License is distributed on an "AS IS" BASIS,
! WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
! See the License for the specific language governing permissions and
! limitations under the License.
!
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    .section ".text"
    .align 8


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! extern "C" int __rw_atomic_xchg32 (int *x, int y);
!
! Atomically assigns the 32-bit value value y to *x and returns
! the original (before assignment) 32-bit value of *x.
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    .type __rw_atomic_xchg32, #function
    .global __rw_atomic_xchg32

__rw_atomic_xchg32:           ! (int *x: %o0, int y: %o1)
    swap    [%o0], %o1        ! *x <-> y
    retl
    mov     %o1, %o0          ! return original value of *x


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! extern "C" int __rw_atomic_add32 (int *x, int y);
!
! Atomically increments the 32-bit value value *x by y and returns
! the new (after increment) 32-bit value of *x.
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    .type __rw_atomic_add32, #function
    .global __rw_atomic_add32

__rw_atomic_add32:            ! (int *x: %o0, int y: %o1)
    mov     -1, %o2           ! INT_MAX is reserved
    srl     %o2, 1, %o2       ! %o2 = -1U >> 1 (== INT_MAX)
.__rw_retry:
    mov     %o2, %o3          ! make a copy for swap 
    swap    [%o0], %o3        ! swap *x for %o3
    cmp     %o3, %o2          ! if *x == INT_MAX (i.e., resource is locked)
    beq,a   .__rw_busywait    !     then busy-wait (else annul next insn)
    nop                       ! else perform add and return
    add     %o3, %o1, %o2     ! %o2 = *x + y
    st      %o2, [%o0]        ! store the sum in *x
    retl                      ! return to caller
    mov     %o2, %o0          ! (delayed) store result in %o0
.__rw_busywait:               ! busy-wait with loads (cheaper than swaps)
    cmp     %o3, %o2          ! if %o3 == INT_MAX
    be      .__rw_busywait    !     then spin
    ld      [%o0], %o3        ! (delayed) %o3 = *x
    ba,a    .__rw_retry       ! otherwise, try again for lock
    nop