UefiCpuPkg: Move AsmRelocateApLoopStart from Mpfuncs.nasm to AmdSev.nasm

[mirror_edk2.git] / OvmfPkg / XenBusDxe / TestAndClearBit.c

/** @file\r
  Implementation of TestAndClearBit using compare-exchange primitive\r
\r
  Copyright (C) 2015, Linaro Ltd.\r
  Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>\r
\r
  SPDX-License-Identifier: BSD-2-Clause-Patent\r
\r
**/\r
\r
#include <Base.h>\r
#include <Library/SynchronizationLib.h>\r
\r
INT32\r
EFIAPI\r
TestAndClearBit (\r
  IN INT32  Bit,\r
  IN VOID   *Address\r
  )\r
{\r
  UINT16  Word, Read;\r
  UINT16  Mask;\r
\r
  //\r
  // Calculate the effective address relative to 'Address' based on the\r
  // higher order bits of 'Bit'. Use signed shift instead of division to\r
  // ensure we round towards -Inf, and end up with a positive shift in\r
  // 'Bit', even if 'Bit' itself is negative.\r
  //\r
  Address = (VOID *)((UINT8 *)Address + ((Bit >> 4) * sizeof (UINT16)));\r
  Mask    = 1U << (Bit & 15);\r
\r
  for (Word = *(UINT16 *)Address; Word &Mask; Word = Read) {\r
    Read = InterlockedCompareExchange16 (Address, Word, Word & ~Mask);\r
    if (Read == Word) {\r
      return 1;\r
    }\r
  }\r
\r
  return 0;\r
}\r