VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitFirstSetU32.asm@ 83743

Last change on this file since 83743 was 82968, checked in by vboxsync, 5 years ago

Copyright year updates by scm.

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1; $Id: ASMBitFirstSetU32.asm 82968 2020-02-04 10:35:17Z vboxsync $
2;; @file
3; IPRT - ASMBitFirstSetU32().
4;
5
6;
7; Copyright (C) 2006-2020 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/asmdefs.mac"
32
33BEGINCODE
34
35;;
36; Finds the first bit which is set in the given 32-bit integer.
37;
38; Bits are numbered from 1 (least significant) to 32.
39;
40; @returns (xAX) index [1..32] of the first set bit.
41; @returns (xAX) 0 if all bits are cleared.
42; @param msc:ecx gcc:edi x86:stack u32 Integer to search for set bits.
43;
44; @cproto DECLASM(unsigned) ASMBitFirstSetU32(uint32_t u32);
45;
46BEGINPROC_EXPORTED ASMBitFirstSetU32
47%if ARCH_BITS == 16
48 CPU 8086
49 push bp
50 mov bp, sp
51
52 ; 15:0
53 mov ax, 1
54 mov cx, [bp + 2 + 2 + 0]
55 test cx, cx
56 jnz .next_bit
57
58 ; 31:16
59 mov al, 16
60 or cx, [bp + 2 + 2 + 2]
61 jz .return_zero
62
63 ; find the bit that was set.
64.next_bit:
65 shr cx, 1
66 jc .return
67 inc ax
68 jmp .next_bit
69
70.return_zero:
71 xor ax, ax
72.return:
73 pop bp
74 ret
75
76%else
77 %if ARCH_BITS == 64
78 %ifdef ASM_CALL64_GCC
79 bsf eax, esi
80 %else
81 bsf eax, ecx
82 %endif
83 %elif ARCH_BITS == 32
84 bsf eax, dword [esp + 4]
85 %else
86 %error "Missing or invalid ARCH_BITS."
87 %endif
88 jz .return_zero
89 inc eax
90.return:
91 ret
92.return_zero:
93 xor eax, eax
94 ret
95%endif
96ENDPROC ASMBitFirstSetU32
97
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