MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange16.c

   1 /** @file
   2   InterlockedCompareExchange16 function
   3
   4   Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
   5   Copyright (c) 2015, Linaro Ltd. All rights reserved.<BR>
   6   This program and the accompanying materials
   7   are licensed and made available under the terms and conditions of the BSD License
   8   which accompanies this distribution.  The full text of the license may be found at
   9   http://opensource.org/licenses/bsd-license.php.
  10
  11   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  12   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  13
  14 **/
  15
  16
  17
  18
  19 /**
  20   Performs an atomic compare exchange operation on a 16-bit unsigned integer.
  21
  22   Performs an atomic compare exchange operation on the 16-bit unsigned integer
  23   specified by Value.  If Value is equal to CompareValue, then Value is set to
  24   ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
  25   then Value is returned.  The compare exchange operation must be performed using
  26   MP safe mechanisms.
  27
  28   @param  Value         A pointer to the 16-bit value for the compare exchange
  29                         operation.
  30   @param  CompareValue  16-bit value used in compare operation.
  31   @param  ExchangeValue 16-bit value used in exchange operation.
  32
  33   @return The original *Value before exchange.
  34
  35 **/
  36 UINT16
  37 EFIAPI
  38 InternalSyncCompareExchange16 (
  39   IN      volatile UINT16           *Value,
  40   IN      UINT16                    CompareValue,
  41   IN      UINT16                    ExchangeValue
  42   )
  43 {
  44   _asm {
  45     mov     ecx, Value
  46     mov     ax, CompareValue
  47     mov     dx, ExchangeValue
  48     lock    cmpxchg [ecx], dx
  49   }
  50 }
  51