1 | ; $Id: ASMBitFirstSetU32.asm 82968 2020-02-04 10:35:17Z vboxsync $
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2 | ;; @file
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3 | ; IPRT - ASMBitFirstSetU32().
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4 | ;
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5 |
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6 | ;
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7 | ; Copyright (C) 2006-2020 Oracle Corporation
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8 | ;
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9 | ; This file is part of VirtualBox Open Source Edition (OSE), as
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10 | ; available from http://www.virtualbox.org. This file is free software;
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11 | ; you can redistribute it and/or modify it under the terms of the GNU
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12 | ; General Public License (GPL) as published by the Free Software
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13 | ; Foundation, in version 2 as it comes in the "COPYING" file of the
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14 | ; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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15 | ; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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16 | ;
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17 | ; The contents of this file may alternatively be used under the terms
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18 | ; of the Common Development and Distribution License Version 1.0
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19 | ; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
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20 | ; VirtualBox OSE distribution, in which case the provisions of the
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21 | ; CDDL are applicable instead of those of the GPL.
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22 | ;
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23 | ; You may elect to license modified versions of this file under the
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24 | ; terms and conditions of either the GPL or the CDDL or both.
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25 | ;
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26 |
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27 |
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28 | ;*******************************************************************************
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29 | ;* Header Files *
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30 | ;*******************************************************************************
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31 | %include "iprt/asmdefs.mac"
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32 |
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33 | BEGINCODE
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34 |
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35 | ;;
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36 | ; Finds the first bit which is set in the given 32-bit integer.
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37 | ;
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38 | ; Bits are numbered from 1 (least significant) to 32.
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39 | ;
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40 | ; @returns (xAX) index [1..32] of the first set bit.
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41 | ; @returns (xAX) 0 if all bits are cleared.
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42 | ; @param msc:ecx gcc:edi x86:stack u32 Integer to search for set bits.
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43 | ;
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44 | ; @cproto DECLASM(unsigned) ASMBitFirstSetU32(uint32_t u32);
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45 | ;
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46 | BEGINPROC_EXPORTED ASMBitFirstSetU32
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47 | %if ARCH_BITS == 16
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48 | CPU 8086
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49 | push bp
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50 | mov bp, sp
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51 |
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52 | ; 15:0
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53 | mov ax, 1
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54 | mov cx, [bp + 2 + 2 + 0]
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55 | test cx, cx
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56 | jnz .next_bit
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57 |
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58 | ; 31:16
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59 | mov al, 16
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60 | or cx, [bp + 2 + 2 + 2]
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61 | jz .return_zero
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62 |
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63 | ; find the bit that was set.
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64 | .next_bit:
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65 | shr cx, 1
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66 | jc .return
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67 | inc ax
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68 | jmp .next_bit
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69 |
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70 | .return_zero:
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71 | xor ax, ax
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72 | .return:
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73 | pop bp
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74 | ret
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75 |
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76 | %else
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77 | %if ARCH_BITS == 64
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78 | %ifdef ASM_CALL64_GCC
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79 | bsf eax, esi
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80 | %else
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81 | bsf eax, ecx
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82 | %endif
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83 | %elif ARCH_BITS == 32
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84 | bsf eax, dword [esp + 4]
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85 | %else
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86 | %error "Missing or invalid ARCH_BITS."
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87 | %endif
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88 | jz .return_zero
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89 | inc eax
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90 | .return:
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91 | ret
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92 | .return_zero:
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93 | xor eax, eax
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94 | ret
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95 | %endif
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96 | ENDPROC ASMBitFirstSetU32
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97 |
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