VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitFirstSet-generic.cpp@ 93943

Last change on this file since 93943 was 93115, checked in by vboxsync, 3 years ago

scm --update-copyright-year

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  • Property svn:keywords set to Author Date Id Revision
File size: 3.2 KB
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1/* $Id: ASMBitFirstSet-generic.cpp 93115 2022-01-01 11:31:46Z vboxsync $ */
2/** @file
3 * IPRT - ASMBitFirstSet - generic C implementation.
4 */
5
6/*
7 * Copyright (C) 2006-2022 Oracle Corporation
8 *
9 * This file is part of VirtualBox Open Source Edition (OSE), as
10 * available from http://www.virtualbox.org. This file is free software;
11 * you can redistribute it and/or modify it under the terms of the GNU
12 * General Public License (GPL) as published by the Free Software
13 * Foundation, in version 2 as it comes in the "COPYING" file of the
14 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
15 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
16 *
17 * The contents of this file may alternatively be used under the terms
18 * of the Common Development and Distribution License Version 1.0
19 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
20 * VirtualBox OSE distribution, in which case the provisions of the
21 * CDDL are applicable instead of those of the GPL.
22 *
23 * You may elect to license modified versions of this file under the
24 * terms and conditions of either the GPL or the CDDL or both.
25 */
26
27
28/*********************************************************************************************************************************
29* Header Files *
30*********************************************************************************************************************************/
31#include <iprt/asm.h>
32#include "internal/iprt.h"
33
34#include <iprt/assert.h>
35
36
37RTDECL(int32_t) ASMBitFirstSet(const volatile void RT_FAR *pvBitmap, uint32_t cBits) RT_NOTHROW_DEF
38{
39 const volatile size_t RT_FAR *pu = (const volatile size_t RT_FAR *)pvBitmap;
40 Assert(!(cBits & 31));
41 Assert(!((uintptr_t)pvBitmap & 3));
42
43#if ARCH_BITS > 32
44 /* Deal with misaligned bitmaps (happens all the time via ASMBitNextClear()). */
45 if (!((uintptr_t)pvBitmap & 7) && cBits >= 32)
46 {
47 uint32_t u32 = *(const volatile uint32_t RT_FAR *)pu;
48 if (u32 != 0)
49 {
50 size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
51 return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u32)) - 1;
52 }
53 pu = (const volatile size_t RT_FAR *)((uintptr_t)pu + sizeof(uint32_t));
54 cBits -= 32;
55 }
56#endif
57
58 /* Main search loop: */
59 while (cBits >= sizeof(size_t) * 8)
60 {
61 size_t u = *pu;
62 if (u == 0)
63 { }
64 else
65 {
66 size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
67#if ARCH_BITS == 32
68 return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u)) - 1;
69#elif ARCH_BITS == 64
70 return iBaseBit + ASMBitFirstSetU64(RT_LE2H_U64(u)) - 1;
71#else
72# error "ARCH_BITS is not supported"
73#endif
74 }
75
76 pu++;
77 cBits -= sizeof(size_t) * 8;
78 }
79
80#if ARCH_BITS > 32
81 /* Final 32-bit item (unlikely)? */
82 if (cBits < 32)
83 { }
84 else
85 {
86 uint32_t u32 = *(const volatile uint32_t RT_FAR *)pu;
87 if (u32 != 0)
88 {
89 size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
90 return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u32)) - 1;
91 }
92 }
93#endif
94
95 return -1;
96}
97
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