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