[mirror_edk2.git] / MdePkg / Library / BaseLib / Synchronization.c

/** @file\r
  Implementation of synchronization functions.\r
\r
  Copyright (c) 2006, Intel Corporation<BR>\r
  All rights reserved. This program and the accompanying materials\r
  are licensed and made available under the terms and conditions of the BSD License\r
  which accompanies this distribution.  The full text of the license may be found at\r
  http://opensource.org/licenses/bsd-license.php\r
\r
  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
\r
  Module Name:  Synchronization.c\r
\r
**/\r
\r
#define SPIN_LOCK_RELEASED          ((SPIN_LOCK)1)\r
#define SPIN_LOCK_ACQUIRED          ((SPIN_LOCK)2)\r
\r
UINT32\r
EFIAPI\r
InternalSyncIncrement (\r
  IN      volatile UINT32           *Value\r
  );\r
\r
UINT32\r
EFIAPI\r
InternalSyncDecrement (\r
  IN      volatile UINT32           *Value\r
  );\r
\r
UINT32\r
EFIAPI\r
InternalSyncCompareExchange32 (\r
  IN      volatile UINT32           *Value,\r
  IN      UINT32                    CompareValue,\r
  IN      UINT32                    ExchangeValue\r
  );\r
\r
UINT64\r
EFIAPI\r
InternalSyncCompareExchange64 (\r
  IN      volatile UINT64           *Value,\r
  IN      UINT64                    CompareValue,\r
  IN      UINT64                    ExchangeValue\r
  );\r
\r
/**\r
  Retrieves the architecture specific spin lock alignment requirements for\r
  optimal spin lock performance.\r
\r
  This function retrieves the spin lock alignment requirements for optimal\r
  performance on a given CPU architecture. The spin lock alignment must be a\r
  power of two and is returned by this function. If there are no alignment\r
  requirements, then 1 must be returned. The spin lock synchronization\r
  functions must function correctly if the spin lock size and alignment values\r
  returned by this function are not used at all. These values are hints to the\r
  consumers of the spin lock synchronization functions to obtain optimal spin\r
  lock performance.\r
\r
  @return The architecture specific spin lock alignment.\r
\r
**/\r
UINTN\r
EFIAPI\r
GetSpinLockProperties (\r
  VOID\r
  )\r
{\r
  // @bug May use a PCD entry to determine this alignment.\r
  return 32;\r
}\r
\r
/**\r
  Initializes a spin lock to the released state and returns the spin lock.\r
\r
  This function initializes the spin lock specified by SpinLock to the released\r
  state, and returns SpinLock. Optimal performance can be achieved by calling\r
  GetSpinLockProperties() to determine the size and alignment requirements for\r
  SpinLock.\r
\r
  If SpinLock is NULL, then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to initialize to the released\r
                    state.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
InitializeSpinLock (\r
  OUT     SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  ASSERT (SpinLock != NULL);\r
  *SpinLock = SPIN_LOCK_RELEASED;\r
  return SpinLock;\r
}\r
\r
/**\r
  Waits until a spin lock can be placed in the acquired state.\r
\r
  This function checks the state of the spin lock specified by SpinLock. If\r
  SpinLock is in the released state, then this function places SpinLock in the\r
  acquired state and returns SpinLock. Otherwise, this function waits\r
  indefinitely for the spin lock to be released, and then places it in the\r
  acquired state and returns SpinLock. All state transitions of SpinLock must\r
  be performed using MP safe mechanisms.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
  If PcdSpinLockTimeout is not zero, and SpinLock is can not be acquired in\r
  PcdSpinLockTimeout microseconds, then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to place in the acquired state.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
AcquireSpinLock (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  UINT64                            Tick;\r
  UINT64                            Start, End;\r
  UINT64                            Timeout;\r
\r
  Tick = 0;\r
  Start = 0;\r
  End = 0;\r
  if (FixedPcdGet32 (PcdSpinLockTimeout) > 0) {\r
    Tick = GetPerformanceCounter ();\r
    Timeout = DivU64x32 (\r
                MultU64x32 (\r
                  GetPerformanceCounterProperties (&Start, &End),\r
                  FixedPcdGet32 (PcdSpinLockTimeout)\r
                  ),\r
                1000000\r
                );\r
    if (Start < End) {\r
      Tick += Timeout;\r
    } else {\r
      Tick -= Timeout;\r
    }\r
  }\r
\r
  while (!AcquireSpinLockOrFail (SpinLock)) {\r
    CpuPause ();\r
    ASSERT ((Start < End) ^ (Tick <= GetPerformanceCounter ()));\r
  }\r
  return SpinLock;\r
}\r
\r
/**\r
  Attempts to place a spin lock in the acquired state.\r
\r
  This function checks the state of the spin lock specified by SpinLock. If\r
  SpinLock is in the released state, then this function places SpinLock in the\r
  acquired state and returns TRUE. Otherwise, FALSE is returned. All state\r
  transitions of SpinLock must be performed using MP safe mechanisms.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to place in the acquired state.\r
\r
  @retval TRUE  SpinLock was placed in the acquired state.\r
  @retval FALSE SpinLock could not be acquired.\r
\r
**/\r
BOOLEAN\r
EFIAPI\r
AcquireSpinLockOrFail (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  ASSERT (SpinLock != NULL);\r
  ASSERT (*SpinLock == SPIN_LOCK_ACQUIRED || *SpinLock == SPIN_LOCK_RELEASED);\r
  return (BOOLEAN)(\r
           InterlockedCompareExchangePointer (\r
             (VOID**)SpinLock,\r
             (VOID*)SPIN_LOCK_RELEASED,\r
             (VOID*)SPIN_LOCK_ACQUIRED\r
             ) == (VOID*)SPIN_LOCK_RELEASED\r
           );\r
}\r
\r
/**\r
  Releases a spin lock.\r
\r
  This function places the spin lock specified by SpinLock in the release state\r
  and returns SpinLock.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to release.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
ReleaseSpinLock (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  ASSERT (SpinLock != NULL);\r
  ASSERT (*SpinLock == SPIN_LOCK_ACQUIRED || *SpinLock == SPIN_LOCK_RELEASED);\r
  *SpinLock = SPIN_LOCK_RELEASED;\r
  return SpinLock;\r
}\r
\r
/**\r
  Performs an atomic increment of an 32-bit unsigned integer.\r
\r
  Performs an atomic increment of the 32-bit unsigned integer specified by\r
  Value and returns the incremented value. The increment operation must be\r
  performed using MP safe mechanisms. The state of the return value is not\r
  guaranteed to be MP safe.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value A pointer to the 32-bit value to increment.\r
\r
  @return The incremented value.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedIncrement (\r
  IN      UINT32                    *Value\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncIncrement (Value);\r
}\r
\r
/**\r
  Performs an atomic decrement of an 32-bit unsigned integer.\r
\r
  Performs an atomic decrement of the 32-bit unsigned integer specified by\r
  Value and returns the decremented value. The decrement operation must be\r
  performed using MP safe mechanisms. The state of the return value is not\r
  guaranteed to be MP safe.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value A pointer to the 32-bit value to decrement.\r
\r
  @return The decremented value.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedDecrement (\r
  IN      UINT32                    *Value\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncDecrement (Value);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a 32-bit unsigned integer.\r
\r
  @param  Value         A pointer to the 32-bit value for the compare exchange\r
                        operation.\r
  @param  CompareValue  32-bit value used in compare operation.\r
  @param  ExchangeValue 32-bit value used in exchange operation.\r
\r
  @return The original *Value before exchange.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedCompareExchange32 (\r
  IN      UINT32                    *Value,\r
  IN      UINT32                    CompareValue,\r
  IN      UINT32                    ExchangeValue\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncCompareExchange32 (Value, CompareValue, ExchangeValue);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a 64-bit unsigned integer.\r
\r
  @param  Value         A pointer to the 64-bit value for the compare exchange\r
                        operation.\r
  @param  CompareValue  64-bit value used in compare operation.\r
  @param  ExchangeValue 64-bit value used in exchange operation.\r
\r
  @return The original *Value before exchange.\r
\r
**/\r
UINT64\r
EFIAPI\r
InterlockedCompareExchange64 (\r
  IN      UINT64                    *Value,\r
  IN      UINT64                    CompareValue,\r
  IN      UINT64                    ExchangeValue\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncCompareExchange64 (Value, CompareValue, ExchangeValue);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a pointer value.\r
\r
  Performs an atomic compare exchange operation on the pointer value specified\r
  by Value. If Value is equal to CompareValue, then Value is set to\r
  ExchangeValue and CompareValue is returned. If Value is not equal to\r
  CompareValue, then Value is returned. The compare exchange operation must be\r
  performed using MP safe mechanisms.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value         A pointer to the pointer value for the compare exchange\r
                        operation.\r
  @param  CompareValue  Pointer value used in compare operation.\r
  @param  ExchangeValue Pointer value used in exchange operation.\r
\r
**/\r
VOID *\r
EFIAPI\r
InterlockedCompareExchangePointer (\r
  IN      VOID                      **Value,\r
  IN      VOID                      *CompareValue,\r
  IN      VOID                      *ExchangeValue\r
  )\r
{\r
  switch (sizeof (*Value)) {\r
    case sizeof (UINT32):\r
      return (VOID*)(UINTN)InterlockedCompareExchange32 (\r
                             (UINT32*)Value,\r
                             (UINT32)(UINTN)CompareValue,\r
                             (UINT32)(UINTN)ExchangeValue\r
                             );\r
    case sizeof (UINT64):\r
      return (VOID*)(UINTN)InterlockedCompareExchange64 (\r
                             (UINT64*)Value,\r
                             (UINT64)(UINTN)CompareValue,\r
                             (UINT64)(UINTN)ExchangeValue\r
                             );\r
    default:\r
      ASSERT (FALSE);\r
      return NULL;\r
  }\r
}\r
Commit	Line	Data
878ddf1f	1	/** @file\r
	2	Implementation of synchronization functions.\r
	3	\r
	4	Copyright (c) 2006, Intel Corporation<BR>\r
	5	All rights reserved. This program and the accompanying materials\r
	6	are licensed and made available under the terms and conditions of the BSD License\r
	7	which accompanies this distribution. The full text of the license may be found at\r
	8	http://opensource.org/licenses/bsd-license.php\r
	9	\r
	10	THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
	11	WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
	12	\r
	13	Module Name: Synchronization.c\r
	14	\r
	15	**/\r
	16	\r
27787243	17	#define SPIN_LOCK_RELEASED ((SPIN_LOCK)1)\r
27787243	18	#define SPIN_LOCK_ACQUIRED ((SPIN_LOCK)2)\r
878ddf1f	19	\r
	20	UINT32\r
	21	EFIAPI\r
	22	InternalSyncIncrement (\r
	23	IN volatile UINT32 *Value\r
	24	);\r
	25	\r
	26	UINT32\r
	27	EFIAPI\r
	28	InternalSyncDecrement (\r
	29	IN volatile UINT32 *Value\r
	30	);\r
	31	\r
	32	UINT32\r
	33	EFIAPI\r
	34	InternalSyncCompareExchange32 (\r
	35	IN volatile UINT32 *Value,\r
	36	IN UINT32 CompareValue,\r
	37	IN UINT32 ExchangeValue\r
	38	);\r
	39	\r
	40	UINT64\r
	41	EFIAPI\r
	42	InternalSyncCompareExchange64 (\r
	43	IN volatile UINT64 *Value,\r
	44	IN UINT64 CompareValue,\r
	45	IN UINT64 ExchangeValue\r
	46	);\r
	47	\r
	48	/**\r
	49	Retrieves the architecture specific spin lock alignment requirements for\r
	50	optimal spin lock performance.\r
	51	\r
	52	This function retrieves the spin lock alignment requirements for optimal\r
	53	performance on a given CPU architecture. The spin lock alignment must be a\r
	54	power of two and is returned by this function. If there are no alignment\r
	55	requirements, then 1 must be returned. The spin lock synchronization\r
	56	functions must function correctly if the spin lock size and alignment values\r
	57	returned by this function are not used at all. These values are hints to the\r
	58	consumers of the spin lock synchronization functions to obtain optimal spin\r
	59	lock performance.\r
	60	\r
	61	@return The architecture specific spin lock alignment.\r
	62	\r
	63	**/\r
	64	UINTN\r
	65	EFIAPI\r
	66	GetSpinLockProperties (\r
	67	VOID\r
	68	)\r
	69	{\r
	70	// @bug May use a PCD entry to determine this alignment.\r
	71	return 32;\r
	72	}\r
	73	\r
	74	/**\r
	75	Initializes a spin lock to the released state and returns the spin lock.\r
	76	\r
	77	This function initializes the spin lock specified by SpinLock to the released\r
	78	state, and returns SpinLock. Optimal performance can be achieved by calling\r
	79	GetSpinLockProperties() to determine the size and alignment requirements for\r
	80	SpinLock.\r
	81	\r
	82	If SpinLock is NULL, then ASSERT().\r
83	\r
84	@param SpinLock A pointer to the spin lock to initialize to the released\r
85	state.\r
86	\r
87	@return SpinLock\r
88	\r
89	**/\r
90	SPIN_LOCK *\r
91	EFIAPI\r
92	InitializeSpinLock (\r
93	OUT SPIN_LOCK *SpinLock\r
94	)\r
95	{\r
96	ASSERT (SpinLock != NULL);\r
27787243	97	*SpinLock = SPIN_LOCK_RELEASED;\r
878ddf1f	98	return SpinLock;\r
	99	}\r
	100	\r
	101	/**\r
	102	Waits until a spin lock can be placed in the acquired state.\r
	103	\r
	104	This function checks the state of the spin lock specified by SpinLock. If\r
	105	SpinLock is in the released state, then this function places SpinLock in the\r
	106	acquired state and returns SpinLock. Otherwise, this function waits\r
	107	indefinitely for the spin lock to be released, and then places it in the\r
	108	acquired state and returns SpinLock. All state transitions of SpinLock must\r
	109	be performed using MP safe mechanisms.\r
	110	\r
	111	If SpinLock is NULL, then ASSERT().\r
	112	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
	113	If PcdSpinLockTimeout is not zero, and SpinLock is can not be acquired in\r
	114	PcdSpinLockTimeout microseconds, then ASSERT().\r
	115	\r
	116	@param SpinLock A pointer to the spin lock to place in the acquired state.\r
	117	\r
	118	@return SpinLock\r
	119	\r
	120	**/\r
	121	SPIN_LOCK *\r
	122	EFIAPI\r
	123	AcquireSpinLock (\r
	124	IN OUT SPIN_LOCK *SpinLock\r
	125	)\r
	126	{\r
	127	UINT64 Tick;\r
	128	UINT64 Start, End;\r
	129	UINT64 Timeout;\r
	130	\r
	131	Tick = 0;\r
	132	Start = 0;\r
	133	End = 0;\r
	134	if (FixedPcdGet32 (PcdSpinLockTimeout) > 0) {\r
	135	Tick = GetPerformanceCounter ();\r
	136	Timeout = DivU64x32 (\r
	137	MultU64x32 (\r
	138	GetPerformanceCounterProperties (&Start, &End),\r
	139	FixedPcdGet32 (PcdSpinLockTimeout)\r
	140	),\r
	141	1000000\r
	142	);\r
	143	if (Start < End) {\r
	144	Tick += Timeout;\r
	145	} else {\r
	146	Tick -= Timeout;\r
	147	}\r
	148	}\r
	149	\r
	150	while (!AcquireSpinLockOrFail (SpinLock)) {\r
	151	CpuPause ();\r
	152	ASSERT ((Start < End) ^ (Tick <= GetPerformanceCounter ()));\r
	153	}\r
	154	return SpinLock;\r
	155	}\r
	156	\r
	157	/**\r
	158	Attempts to place a spin lock in the acquired state.\r
	159	\r
	160	This function checks the state of the spin lock specified by SpinLock. If\r
	161	SpinLock is in the released state, then this function places SpinLock in the\r
162	acquired state and returns TRUE. Otherwise, FALSE is returned. All state\r
163	transitions of SpinLock must be performed using MP safe mechanisms.\r
164	\r
165	If SpinLock is NULL, then ASSERT().\r
166	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
167	\r
168	@param SpinLock A pointer to the spin lock to place in the acquired state.\r
169	\r
170	@retval TRUE SpinLock was placed in the acquired state.\r
171	@retval FALSE SpinLock could not be acquired.\r
172	\r
173	**/\r
174	BOOLEAN\r
175	EFIAPI\r
176	AcquireSpinLockOrFail (\r
177	IN OUT SPIN_LOCK *SpinLock\r
178	)\r
179	{\r
180	ASSERT (SpinLock != NULL);\r
27787243	181	ASSERT (SpinLock == SPIN_LOCK_ACQUIRED \|\| SpinLock == SPIN_LOCK_RELEASED);\r
878ddf1f	182	return (BOOLEAN)(\r
	183	InterlockedCompareExchangePointer (\r
	184	(VOID**)SpinLock,\r
	185	(VOID*)SPIN_LOCK_RELEASED,\r
	186	(VOID*)SPIN_LOCK_ACQUIRED\r
	187	) == (VOID*)SPIN_LOCK_RELEASED\r
	188	);\r
	189	}\r
	190	\r
	191	/**\r
	192	Releases a spin lock.\r
	193	\r
	194	This function places the spin lock specified by SpinLock in the release state\r
	195	and returns SpinLock.\r
	196	\r
	197	If SpinLock is NULL, then ASSERT().\r
	198	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
	199	\r
	200	@param SpinLock A pointer to the spin lock to release.\r
	201	\r
	202	@return SpinLock\r
	203	\r
	204	**/\r
	205	SPIN_LOCK *\r
	206	EFIAPI\r
	207	ReleaseSpinLock (\r
	208	IN OUT SPIN_LOCK *SpinLock\r
	209	)\r
	210	{\r
	211	ASSERT (SpinLock != NULL);\r
27787243	212	ASSERT (SpinLock == SPIN_LOCK_ACQUIRED \|\| SpinLock == SPIN_LOCK_RELEASED);\r
27787243	213	*SpinLock = SPIN_LOCK_RELEASED;\r
878ddf1f	214	return SpinLock;\r
	215	}\r
	216	\r
	217	/**\r
	218	Performs an atomic increment of an 32-bit unsigned integer.\r
	219	\r
	220	Performs an atomic increment of the 32-bit unsigned integer specified by\r
	221	Value and returns the incremented value. The increment operation must be\r
	222	performed using MP safe mechanisms. The state of the return value is not\r
	223	guaranteed to be MP safe.\r
	224	\r
	225	If Value is NULL, then ASSERT().\r
	226	\r
	227	@param Value A pointer to the 32-bit value to increment.\r
	228	\r
	229	@return The incremented value.\r
	230	\r
	231	**/\r
	232	UINT32\r
	233	EFIAPI\r
	234	InterlockedIncrement (\r
	235	IN UINT32 *Value\r
	236	)\r
	237	{\r
	238	ASSERT (Value != NULL);\r
	239	return InternalSyncIncrement (Value);\r
	240	}\r
	241	\r
	242	/**\r
	243	Performs an atomic decrement of an 32-bit unsigned integer.\r
	244	\r
	245	Performs an atomic decrement of the 32-bit unsigned integer specified by\r
	246	Value and returns the decremented value. The decrement operation must be\r
	247	performed using MP safe mechanisms. The state of the return value is not\r
	248	guaranteed to be MP safe.\r
	249	\r
	250	If Value is NULL, then ASSERT().\r
	251	\r
	252	@param Value A pointer to the 32-bit value to decrement.\r
	253	\r
	254	@return The decremented value.\r
	255	\r
	256	**/\r
	257	UINT32\r
	258	EFIAPI\r
	259	InterlockedDecrement (\r
	260	IN UINT32 *Value\r
	261	)\r
	262	{\r
	263	ASSERT (Value != NULL);\r
	264	return InternalSyncDecrement (Value);\r
	265	}\r
	266	\r
	267	/**\r
	268	Performs an atomic compare exchange operation on a 32-bit unsigned integer.\r
	269	\r
	270	@param Value A pointer to the 32-bit value for the compare exchange\r
	271	operation.\r
	272	@param CompareValue 32-bit value used in compare operation.\r
	273	@param ExchangeValue 32-bit value used in exchange operation.\r
	274	\r
	275	@return The original *Value before exchange.\r
	276	\r
	277	**/\r
278	UINT32\r
279	EFIAPI\r
280	InterlockedCompareExchange32 (\r
281	IN UINT32 *Value,\r
282	IN UINT32 CompareValue,\r
283	IN UINT32 ExchangeValue\r
284	)\r
285	{\r
286	ASSERT (Value != NULL);\r
287	return InternalSyncCompareExchange32 (Value, CompareValue, ExchangeValue);\r
288	}\r
289	\r
290	/**\r
291	Performs an atomic compare exchange operation on a 64-bit unsigned integer.\r
292	\r
293	@param Value A pointer to the 64-bit value for the compare exchange\r
294	operation.\r
295	@param CompareValue 64-bit value used in compare operation.\r
296	@param ExchangeValue 64-bit value used in exchange operation.\r
297	\r
298	@return The original *Value before exchange.\r
299	\r
300	**/\r
301	UINT64\r
302	EFIAPI\r
303	InterlockedCompareExchange64 (\r
304	IN UINT64 *Value,\r
305	IN UINT64 CompareValue,\r
306	IN UINT64 ExchangeValue\r
307	)\r
308	{\r
309	ASSERT (Value != NULL);\r
310	return InternalSyncCompareExchange64 (Value, CompareValue, ExchangeValue);\r
311	}\r
312	\r
313	/**\r
314	Performs an atomic compare exchange operation on a pointer value.\r
315	\r
316	Performs an atomic compare exchange operation on the pointer value specified\r
317	by Value. If Value is equal to CompareValue, then Value is set to\r
318	ExchangeValue and CompareValue is returned. If Value is not equal to\r
319	CompareValue, then Value is returned. The compare exchange operation must be\r
320	performed using MP safe mechanisms.\r
321	\r
322	If Value is NULL, then ASSERT().\r
323	\r
324	@param Value A pointer to the pointer value for the compare exchange\r
325	operation.\r
326	@param CompareValue Pointer value used in compare operation.\r
327	@param ExchangeValue Pointer value used in exchange operation.\r
328	\r
329	**/\r
330	VOID *\r
331	EFIAPI\r
332	InterlockedCompareExchangePointer (\r
333	IN VOID **Value,\r
334	IN VOID *CompareValue,\r
335	IN VOID *ExchangeValue\r
336	)\r
337	{\r
338	switch (sizeof (*Value)) {\r
339	case sizeof (UINT32):\r
340	return (VOID*)(UINTN)InterlockedCompareExchange32 (\r
341	(UINT32*)Value,\r
342	(UINT32)(UINTN)CompareValue,\r
343	(UINT32)(UINTN)ExchangeValue\r
344	);\r
345	case sizeof (UINT64):\r
346	return (VOID*)(UINTN)InterlockedCompareExchange64 (\r
347	(UINT64*)Value,\r
348	(UINT64)(UINTN)CompareValue,\r
349	(UINT64)(UINTN)ExchangeValue\r
350	);\r
351	default:\r
352	ASSERT (FALSE);\r
353	return NULL;\r
354	}\r
355	}\r