1 | /* $Id: ASMBitFirstSet-generic.cpp 98103 2023-01-17 14:15:46Z vboxsync $ */
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2 | /** @file
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3 | * IPRT - ASMBitFirstSet - generic C implementation.
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4 | */
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5 |
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6 | /*
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7 | * Copyright (C) 2006-2023 Oracle and/or its affiliates.
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8 | *
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9 | * This file is part of VirtualBox base platform packages, as
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10 | * available from https://www.virtualbox.org.
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11 | *
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12 | * This program is free software; you can redistribute it and/or
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13 | * modify it under the terms of the GNU General Public License
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14 | * as published by the Free Software Foundation, in version 3 of the
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15 | * License.
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16 | *
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17 | * This program is distributed in the hope that it will be useful, but
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18 | * WITHOUT ANY WARRANTY; without even the implied warranty of
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19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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20 | * General Public License for more details.
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21 | *
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22 | * You should have received a copy of the GNU General Public License
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23 | * along with this program; if not, see <https://www.gnu.org/licenses>.
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24 | *
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25 | * The contents of this file may alternatively be used under the terms
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26 | * of the Common Development and Distribution License Version 1.0
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27 | * (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
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28 | * in the VirtualBox distribution, in which case the provisions of the
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29 | * CDDL are applicable instead of those of the GPL.
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30 | *
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31 | * You may elect to license modified versions of this file under the
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32 | * terms and conditions of either the GPL or the CDDL or both.
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33 | *
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34 | * SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
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35 | */
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36 |
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37 |
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38 | /*********************************************************************************************************************************
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39 | * Header Files *
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40 | *********************************************************************************************************************************/
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41 | #include <iprt/asm.h>
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42 | #include "internal/iprt.h"
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43 |
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44 | #include <iprt/assert.h>
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45 |
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46 |
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47 | RTDECL(int32_t) ASMBitFirstSet(const volatile void RT_FAR *pvBitmap, uint32_t cBits) RT_NOTHROW_DEF
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48 | {
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49 | const volatile size_t RT_FAR *pu = (const volatile size_t RT_FAR *)pvBitmap;
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50 | Assert(!(cBits & 31));
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51 | Assert(!((uintptr_t)pvBitmap & 3));
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52 |
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53 | #if ARCH_BITS > 32
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54 | /* Deal with misaligned bitmaps (happens all the time via ASMBitNextClear()). */
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55 | if (!((uintptr_t)pvBitmap & 7) && cBits >= 32)
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56 | {
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57 | uint32_t u32 = *(const volatile uint32_t RT_FAR *)pu;
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58 | if (u32 != 0)
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59 | {
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60 | size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
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61 | return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u32)) - 1;
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62 | }
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63 | pu = (const volatile size_t RT_FAR *)((uintptr_t)pu + sizeof(uint32_t));
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64 | cBits -= 32;
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65 | }
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66 | #endif
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67 |
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68 | /* Main search loop: */
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69 | while (cBits >= sizeof(size_t) * 8)
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70 | {
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71 | size_t u = *pu;
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72 | if (u == 0)
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73 | { }
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74 | else
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75 | {
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76 | size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
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77 | #if ARCH_BITS == 32
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78 | return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u)) - 1;
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79 | #elif ARCH_BITS == 64
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80 | return iBaseBit + ASMBitFirstSetU64(RT_LE2H_U64(u)) - 1;
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81 | #else
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82 | # error "ARCH_BITS is not supported"
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83 | #endif
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84 | }
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85 |
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86 | pu++;
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87 | cBits -= sizeof(size_t) * 8;
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88 | }
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89 |
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90 | #if ARCH_BITS > 32
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91 | /* Final 32-bit item (unlikely)? */
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92 | if (cBits < 32)
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93 | { }
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94 | else
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95 | {
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96 | uint32_t u32 = *(const volatile uint32_t RT_FAR *)pu;
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97 | if (u32 != 0)
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98 | {
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99 | size_t const iBaseBit = ((uintptr_t)pu - (uintptr_t)pvBitmap) * 8;
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100 | return iBaseBit + ASMBitFirstSetU32(RT_LE2H_U32(u32)) - 1;
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101 | }
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102 | }
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103 | #endif
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104 |
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105 | return -1;
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106 | }
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107 |
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