272 //
273 // Inspecting the return value is the only way for the caller to determine
274 // if the compare-and-swap instruction was successful:
275 // - If return value and compare value compare equal, the compare-and-swap
276 // instruction was successful and the value in memory was replaced by the
277 // exchange value.
278 // - If return value and compare value compare unequal, the compare-and-swap
279 // instruction was not successful. The value in memory was left unchanged.
280 //
281 // The s390 processors always fence before and after the csg instructions.
282 // Thus we ignore the memory ordering argument. The docu says: "A serialization
283 // function is performed before the operand is fetched and again after the
284 // operation is completed."
285
286 // No direct support for cmpxchg of bytes; emulate using int.
287 template<>
288 struct Atomic::PlatformCmpxchg<1> : Atomic::CmpxchgByteUsingInt {};
289
290 template<>
291 template<typename T>
292 inline T Atomic::PlatformCmpxchg<4>::operator()(T xchg_val,
293 T volatile* dest,
294 T cmp_val,
295 atomic_memory_order unused) const {
296 STATIC_ASSERT(4 == sizeof(T));
297 T old;
298
299 __asm__ __volatile__ (
300 " CS %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
301 // outputs
302 : [old] "=&d" (old) // Write-only, prev value irrelevant.
303 , [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
304 // inputs
305 : [upd] "d" (xchg_val)
306 , "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
307 // clobbered
308 : "cc", "memory"
309 );
310
311 return old;
312 }
313
314 template<>
315 template<typename T>
316 inline T Atomic::PlatformCmpxchg<8>::operator()(T xchg_val,
317 T volatile* dest,
318 T cmp_val,
319 atomic_memory_order unused) const {
320 STATIC_ASSERT(8 == sizeof(T));
321 T old;
322
323 __asm__ __volatile__ (
324 " CSG %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
325 // outputs
326 : [old] "=&d" (old) // Write-only, prev value irrelevant.
327 , [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
328 // inputs
329 : [upd] "d" (xchg_val)
330 , "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
331 // clobbered
332 : "cc", "memory"
333 );
334
335 return old;
336 }
337
338 template<size_t byte_size>
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272 //
273 // Inspecting the return value is the only way for the caller to determine
274 // if the compare-and-swap instruction was successful:
275 // - If return value and compare value compare equal, the compare-and-swap
276 // instruction was successful and the value in memory was replaced by the
277 // exchange value.
278 // - If return value and compare value compare unequal, the compare-and-swap
279 // instruction was not successful. The value in memory was left unchanged.
280 //
281 // The s390 processors always fence before and after the csg instructions.
282 // Thus we ignore the memory ordering argument. The docu says: "A serialization
283 // function is performed before the operand is fetched and again after the
284 // operation is completed."
285
286 // No direct support for cmpxchg of bytes; emulate using int.
287 template<>
288 struct Atomic::PlatformCmpxchg<1> : Atomic::CmpxchgByteUsingInt {};
289
290 template<>
291 template<typename T>
292 inline T Atomic::PlatformCmpxchg<4>::operator()(T volatile* dest,
293 T cmp_val,
294 T xchg_val,
295 atomic_memory_order unused) const {
296 STATIC_ASSERT(4 == sizeof(T));
297 T old;
298
299 __asm__ __volatile__ (
300 " CS %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
301 // outputs
302 : [old] "=&d" (old) // Write-only, prev value irrelevant.
303 , [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
304 // inputs
305 : [upd] "d" (xchg_val)
306 , "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
307 // clobbered
308 : "cc", "memory"
309 );
310
311 return old;
312 }
313
314 template<>
315 template<typename T>
316 inline T Atomic::PlatformCmpxchg<8>::operator()(T volatile* dest,
317 T cmp_val,
318 T xchg_val,
319 atomic_memory_order unused) const {
320 STATIC_ASSERT(8 == sizeof(T));
321 T old;
322
323 __asm__ __volatile__ (
324 " CSG %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
325 // outputs
326 : [old] "=&d" (old) // Write-only, prev value irrelevant.
327 , [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
328 // inputs
329 : [upd] "d" (xchg_val)
330 , "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
331 // clobbered
332 : "cc", "memory"
333 );
334
335 return old;
336 }
337
338 template<size_t byte_size>
|