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