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   SPDX-License-Identifier: BSD-2-Clause-Patent
   7
   8 **/
   9
  10
  11
  12
  13 /**
  14   Performs an atomic compare exchange operation on a 16-bit unsigned integer.
  15
  16   Performs an atomic compare exchange operation on the 16-bit unsigned integer
  17   specified by Value.  If Value is equal to CompareValue, then Value is set to
  18   ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
  19   then Value is returned.  The compare exchange operation must be performed using
  20   MP safe mechanisms.
  21
  22   @param  Value         A pointer to the 16-bit value for the compare exchange
  23                         operation.
  24   @param  CompareValue  16-bit value used in compare operation.
  25   @param  ExchangeValue 16-bit value used in exchange operation.
  26
  27   @return The original *Value before exchange.
  28
  29 **/
  30 UINT16
  31 EFIAPI
  32 InternalSyncCompareExchange16 (
  33   IN      volatile UINT16           *Value,
  34   IN      UINT16                    CompareValue,
  35   IN      UINT16                    ExchangeValue
  36   )
  37 {
  38   _asm {
  39     mov     ecx, Value
  40     mov     ax, CompareValue
  41     mov     dx, ExchangeValue
  42     lock    cmpxchg [ecx], dx
  43   }
  44 }
  45