1 /** @file
2   Implementation of TestAndClearBit using compare-exchange primitive
3 
4   Copyright (C) 2015, Linaro Ltd.
5   Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
6 
7   SPDX-License-Identifier: BSD-2-Clause-Patent
8 
9 **/
10 
11 #include <Base.h>
12 #include <Library/SynchronizationLib.h>
13 
14 INT32
15 EFIAPI
TestAndClearBit(IN INT32 Bit,IN VOID * Address)16 TestAndClearBit (
17   IN INT32            Bit,
18   IN VOID             *Address
19   )
20 {
21   UINT16    Word, Read;
22   UINT16    Mask;
23 
24   //
25   // Calculate the effective address relative to 'Address' based on the
26   // higher order bits of 'Bit'. Use signed shift instead of division to
27   // ensure we round towards -Inf, and end up with a positive shift in
28   // 'Bit', even if 'Bit' itself is negative.
29   //
30   Address = (VOID*)((UINT8*) Address + ((Bit >> 4) * sizeof(UINT16)));
31   Mask = 1U << (Bit & 15);
32 
33   for (Word = *(UINT16 *) Address; Word & Mask; Word = Read) {
34     Read = InterlockedCompareExchange16 (Address, Word, Word & ~Mask);
35     if (Read == Word) {
36       return 1;
37     }
38   }
39   return 0;
40 }
41