1 | ; $Id: ASMBitFirstClear.asm 98103 2023-01-17 14:15:46Z vboxsync $
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2 | ;; @file
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3 | ; IPRT - ASMBitFirstClear().
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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/asmdefs.mac"
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42 |
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43 | BEGINCODE
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44 |
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45 | ;;
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46 | ; Finds the first clear bit in a bitmap.
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47 | ;
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48 | ; @returns (32/64:eax, 16:ax+dx) Index of the first zero bit.
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49 | ; @returns (32/64:eax, 16:ax+dx) -1 if no clear bit was found.
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50 | ; @param msc:rcx gcc:rdi pvBitmap Pointer to the bitmap.
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51 | ; @param msc:edx gcc:rsi cBits The number of bits in the bitmap. Multiple of 32.
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52 | ;
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53 | RT_BEGINPROC ASMBitFirstClear
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54 | ;
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55 | ; if (cBits)
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56 | ; Put cBits in ecx first.
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57 | ;
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58 | %if ARCH_BITS == 64
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59 | %ifdef ASM_CALL64_GCC
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60 | mov ecx, esi
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61 | %else
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62 | xchg rcx, rdx ; rdx=pvDst, ecx=cBits
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63 | %endif
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64 | %elif ARCH_BITS == 32
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65 | mov ecx, [esp + 4 + 4]
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66 | %elif ARCH_BITS == 16
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67 | push bp
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68 | mov bp, sp
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69 | mov ecx, [bp + 4 + 4]
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70 | %endif
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71 | or ecx, ecx
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72 | jz short .failed
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73 | ;{
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74 | push xDI
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75 |
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76 | ; asm {...}
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77 | %if ARCH_BITS == 64
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78 | %ifdef ASM_CALL64_GCC
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79 | ; rdi = start of scasd - already done
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80 | %else
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81 | mov rdi, rdx ; rdi = start of scasd (Note! xchg rdx,rcx above)
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82 | %endif
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83 | %elif ARCH_BITS == 32
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84 | mov edi, [esp + 8]
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85 | %elif ARCH_BITS == 16
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86 | mov ax, [bp + 4 + 2]
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87 | mov di, [bp + 4]
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88 | mov es, ax ; es is volatile, no need to save.
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89 | %endif
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90 | add ecx, 31 ; 32 bit aligned
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91 | shr ecx, 5 ; number of dwords to scan.
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92 | mov xDX, xDI ; xDX = saved pvBitmap
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93 | mov eax, 0ffffffffh
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94 | repe scasd ; Scan for the first dword with any clear bit.
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95 | je .failed_restore
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96 |
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97 | ; find the bit in question
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98 | sub xDI, 4 ; one step back.
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99 | %if ARCH_BITS == 16
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100 | movzx edi, di
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101 | xor eax, [es:xDI] ; eax = NOT [rdi]
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102 | %else
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103 | xor eax, [xDI] ; eax = NOT [rdi]
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104 | %endif
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105 | sub xDI, xDX
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106 | shl edi, 3 ; calc bit offset.
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107 |
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108 | bsf ecx, eax
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109 | jz .failed_restore ; race paranoia
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110 | add ecx, edi
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111 | mov eax, ecx
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112 |
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113 | ; return success
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114 | pop xDI
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115 | %if ARCH_BITS == 16
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116 | mov edx, eax
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117 | shr edx, 16
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118 | leave
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119 | %endif
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120 | ret
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121 |
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122 | ; failure
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123 | ;}
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124 | ;return -1;
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125 | .failed_restore:
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126 | pop xDI
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127 | .failed:
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128 | %if ARCH_BITS != 16
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129 | mov eax, 0ffffffffh
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130 | %else
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131 | mov ax, 0ffffh
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132 | mov dx, ax
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133 | leave
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134 | %endif
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135 | ret
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136 | ENDPROC ASMBitFirstClear
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137 |
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