audk/MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange16.c

/** @file
  InterlockedCompareExchange16 function

  Copyright (c) 2006 - 2010, Intel Corporation. All rights reserved.<BR>
  Copyright (c) 2015, Linaro Ltd. All rights reserved.<BR>
  This program and the accompanying materials
  are licensed and made available under the terms and conditions of the BSD License
  which accompanies this distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php.

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/




/**
  Performs an atomic compare exchange operation on a 16-bit unsigned integer.

  Performs an atomic compare exchange operation on the 16-bit unsigned integer
  specified by Value.  If Value is equal to CompareValue, then Value is set to
  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
  then Value is returned.  The compare exchange operation must be performed using
  MP safe mechanisms.

  @param  Value         A pointer to the 16-bit value for the compare exchange
                        operation.
  @param  CompareValue  16-bit value used in compare operation.
  @param  ExchangeValue 16-bit value used in exchange operation.

  @return The original *Value before exchange.

**/
UINT16
EFIAPI
InternalSyncCompareExchange16 (
  IN      UINT16                    *Value,
  IN      UINT16                    CompareValue,
  IN      UINT16                    ExchangeValue
  )
{
  _asm {
    mov     ecx, Value
    mov     ax, CompareValue
    mov     dx, ExchangeValue
    lock    cmpxchg [ecx], dx
  }
}