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/** @file
Implementation of TestAndClearBit using compare-exchange primitive
Copyright (C) 2015, Linaro Ltd.
Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
#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;
}
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