1 | ; $Id: ASMBitLastSetU64.asm 98103 2023-01-17 14:15:46Z vboxsync $
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2 | ;; @file
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3 | ; IPRT - ASMBitLastSetU64().
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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 last bit which is set in the given 64-bit integer.
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47 | ;
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48 | ; Bits are numbered from 1 (least significant) to 64.
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49 | ;
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50 | ; @returns (xAX) index [1..64] of the last set bit.
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51 | ; @returns (xAX) 0 if all bits are cleared.
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52 | ; @param msc:rcx gcc:rdi x86:stack u64 Integer to search for set bits.
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53 | ;
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54 | ; @cproto DECLASM(unsigned) ASMBitLastSetU64(uint64_t u64);
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55 | ;
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56 | RT_BEGINPROC ASMBitLastSetU64
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57 | %if ARCH_BITS == 16
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58 | CPU 8086
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59 | push bp
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60 | mov bp, sp
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61 |
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62 | ; 63:48
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63 | mov ax, 64
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64 | mov cx, [bp + 2 + 2 + 6]
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65 | test cx, cx
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66 | jnz .next_bit
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67 |
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68 | ; 47:32
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69 | mov al, 48
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70 | or cx, [bp + 2 + 2 + 4]
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71 | jnz .next_bit
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72 |
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73 | ; 31:16
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74 | mov al, 32
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75 | or cx, [bp + 2 + 2 + 2]
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76 | jnz .next_bit
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77 |
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78 | ; 16:0
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79 | mov al, 16
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80 | or cx, [bp + 2 + 2 + 0]
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81 | jz .return_zero
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82 |
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83 | ; find the bit that was set.
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84 | .next_bit:
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85 | shl cx, 1
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86 | jc .return
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87 | dec ax
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88 | jmp .next_bit
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89 |
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90 | .return_zero:
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91 | xor ax, ax
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92 | .return:
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93 | pop bp
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94 | ret
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95 |
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96 | %else
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97 | %if ARCH_BITS == 64
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98 | %ifdef ASM_CALL64_GCC
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99 | bsr rax, rsi
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100 | %else
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101 | bsr rax, rcx
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102 | %endif
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103 | jz .return_zero
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104 | inc eax
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105 | .return:
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106 | ret
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107 |
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108 | %elif ARCH_BITS == 32
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109 | ; Check the 2nd dword then the first one.
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110 | bsr eax, dword [esp + 4 + 4]
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111 | jz .check_1st_dword
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112 | add eax, 32
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113 | ret
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114 |
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115 | .check_1st_dword:
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116 | bsr eax, dword [esp + 4 + 0]
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117 | jz .return_zero
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118 | inc eax
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119 | ret
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120 |
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121 | %else
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122 | %error "Missing or invalid ARCH_BITS."
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123 | %endif
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124 |
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125 | .return_zero:
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126 | xor eax, eax
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127 | ret
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128 | %endif
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129 | ENDPROC ASMBitLastSetU64
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130 |
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