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