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 ! -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-

 ! 

 ! This Source Code Form is subject to the terms of the Mozilla Public

 ! License, v. 2.0. If a copy of the MPL was not distributed with this

 ! file, You can obtain one at http://mozilla.org/MPL/2.0/.

 !

 !  atomic increment, decrement and swap routines for V8+ sparc (ultrasparc)

 !  using CAS (compare-and-swap) atomic instructions

 !

 !  this MUST be compiled with an ultrasparc-aware assembler

 !

 !  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 = a + 1 atomically with respect to other

 !  fetch-and-adds to location a in a wait-free fashion.

 !

 !  usage : val = PR_AtomicIncrement(address)

 !  return: current value (you'd think this would be old val)

 !

 !  -----------------------

 !  Note on REGISTER USAGE:

 !  as this is a LEAF procedure, a new stack frame is not created;

 !  we use the caller's 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  [local]   - work register

 !     %o2  [local]   - work register

 !     %o3  [local]   - work register

 !  -----------------------

         ENTRY(PR_AtomicIncrement)       ! standard assembler/ELF prologue

 retryAI:

         ld      [%o0], %o2              ! set o2 to the current value

         add     %o2, 0x1, %o3           ! calc the new value

         mov     %o3, %o1                ! save the return value

         cas     [%o0], %o2, %o3         ! atomically set if o0 hasn't changed

         cmp     %o2, %o3                ! see if we set the value

         bne     retryAI                 ! if not, try again

         nop                             ! empty out the branch pipeline

         retl                            ! return back to the caller

         mov     %o1, %o0                ! set the return code to the new value

         SET_SIZE(PR_AtomicIncrement)    ! standard assembler/ELF epilogue

 !

 !  end

 !

 !  ======================================================================

 !

 !  ======================================================================

 !

 !  Perform the sequence a = a - 1 atomically with respect to other

 !  fetch-and-decs to location a in a wait-free fashion.

 !

 !  usage : val = PR_AtomicDecrement(address)

 !  return: current value (you'd think this would be old val)

 !

 !  -----------------------

 !  Note on REGISTER USAGE:

 !  as this is a LEAF procedure, a new stack frame is not created;

 !  we use the caller's 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  [local]   - work register

 !     %o2  [local]   - work register

 !     %o3  [local]   - work register

 !  -----------------------

         ENTRY(PR_AtomicDecrement)       ! standard assembler/ELF prologue

 retryAD:

         ld      [%o0], %o2              ! set o2 to the current value

         sub     %o2, 0x1, %o3           ! calc the new value

         mov     %o3, %o1                ! save the return value

         cas     [%o0], %o2, %o3         ! atomically set if o0 hasn't changed

         cmp     %o2, %o3                ! see if we set the value

         bne     retryAD                 ! if not, try again

         nop                             ! empty out the branch pipeline

         retl                            ! return back to the caller

         mov     %o1, %o0                ! set the return code to the new value

         SET_SIZE(PR_AtomicDecrement)    ! standard assembler/ELF epilogue

 !

 !  end

 !

 !  ======================================================================

 !

 !  ======================================================================

 !

 !  Perform the sequence a = b atomically with respect to other

 !  fetch-and-stores to location a in a wait-free fashion.

 !

 !  usage : old_val = PR_AtomicSet(address, newval)

 !

 !  -----------------------

 !  Note on REGISTER USAGE:

 !  as this is a LEAF procedure, a new stack frame is not created;

 !  we use the caller's 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 new value to set for [%o0]

 !     %o2  [local]   - work register

 !     %o3  [local]   - work register

 !  -----------------------

         ENTRY(PR_AtomicSet)             ! standard assembler/ELF prologue

 retryAS:

         ld      [%o0], %o2              ! set o2 to the current value

         mov     %o1, %o3                ! set up the new value

         cas     [%o0], %o2, %o3         ! atomically set if o0 hasn't changed

         cmp     %o2, %o3                ! see if we set the value

         bne     retryAS                 ! if not, try again

         nop                             ! empty out the branch pipeline

         retl                            ! return back to the caller

         mov     %o3, %o0                ! set the return code to the prev value

         SET_SIZE(PR_AtomicSet)          ! standard assembler/ELF epilogue

 !

 !  end

 !

 !  ======================================================================

 !

 !  ======================================================================

 !

 !  Perform the sequence a = a + b atomically with respect to other

 !  fetch-and-adds to location a in a wait-free fashion.

 !

 !  usage : newval = PR_AtomicAdd(address, val)

 !  return: the value after addition

 !

         ENTRY(PR_AtomicAdd)       ! standard assembler/ELF prologue

 retryAA:

         ld      [%o0], %o2              ! set o2 to the current value

         add     %o2, %o1, %o3           ! calc the new value

         mov     %o3, %o4                ! save the return value

         cas     [%o0], %o2, %o3         ! atomically set if o0 hasn't changed

         cmp     %o2, %o3                ! see if we set the value

         bne     retryAA                 ! if not, try again

         nop                             ! empty out the branch pipeline

         retl                            ! return back to the caller

         mov     %o4, %o0                ! set the return code to the new value

         SET_SIZE(PR_AtomicAdd)    		! standard assembler/ELF epilogue

 !

 !  end

 !