VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitFirstSet.asm@ 103795

Last change on this file since 103795 was 98103, checked in by vboxsync, 2 years ago

Copyright year updates by scm.

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1; $Id: ASMBitFirstSet.asm 98103 2023-01-17 14:15:46Z vboxsync $
2;; @file
3; IPRT - ASMBitFirstSet().
4;
5
6;
7; Copyright (C) 2006-2023 Oracle and/or its affiliates.
8;
9; This file is part of VirtualBox base platform packages, as
10; available from https://www.virtualbox.org.
11;
12; This program is free software; you can redistribute it and/or
13; modify it under the terms of the GNU General Public License
14; as published by the Free Software Foundation, in version 3 of the
15; License.
16;
17; This program is distributed in the hope that it will be useful, but
18; WITHOUT ANY WARRANTY; without even the implied warranty of
19; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20; General Public License for more details.
21;
22; You should have received a copy of the GNU General Public License
23; along with this program; if not, see <https://www.gnu.org/licenses>.
24;
25; The contents of this file may alternatively be used under the terms
26; of the Common Development and Distribution License Version 1.0
27; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
28; in the VirtualBox distribution, in which case the provisions of the
29; CDDL are applicable instead of those of the GPL.
30;
31; You may elect to license modified versions of this file under the
32; terms and conditions of either the GPL or the CDDL or both.
33;
34; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
35;
36
37
38;*******************************************************************************
39;* Header Files *
40;*******************************************************************************
41%include "iprt/asmdefs.mac"
42
43BEGINCODE
44
45;;
46; Finds the first set bit in a bitmap.
47;
48; @returns (32/64:eax, 16:ax+dx) Index of the first zero bit.
49; @returns (32/64:eax, 16:ax+dx) -1 if no set bit was found.
50; @param msc:rcx gcc:rdi pvBitmap Pointer to the bitmap.
51; @param msc:edx gcc:rsi cBits The number of bits in the bitmap. Multiple of 32.
52;
53RT_BEGINPROC ASMBitFirstSet
54 ;
55 ; if (cBits)
56 ; Put cBits in ecx first.
57 ;
58%if ARCH_BITS == 64
59 %ifdef ASM_CALL64_GCC
60 mov ecx, esi
61 %else
62 xchg rcx, rdx ; rdx=pvDst, ecx=cBits
63 %endif
64%elif ARCH_BITS == 32
65 mov ecx, [esp + 4 + 4]
66%elif ARCH_BITS == 16
67 push bp
68 mov bp, sp
69 mov ecx, [bp + 4 + 4]
70%endif
71 or ecx, ecx
72 jz short .failed
73 ;{
74 push xDI
75
76 ; asm {...}
77%if ARCH_BITS == 64
78 %ifdef ASM_CALL64_GCC
79 ; rdi = start of scasd - already done
80 %else
81 mov rdi, rdx ; rdi = start of scasd (Note! xchg rdx,rcx above)
82 %endif
83%elif ARCH_BITS == 32
84 mov edi, [esp + 4]
85%elif ARCH_BITS == 16
86 mov ax, [bp + 4 + 2]
87 mov di, [bp + 4]
88 mov es, ax ; es is volatile, no need to save.
89%endif
90 add ecx, 31 ; 32 bit aligned
91 shr ecx, 5 ; number of dwords to scan.
92 mov xDX, xDI ; xDX = saved pvBitmap
93 xor eax, eax
94 repe scasd ; Scan for the first dword with any bit set.
95 je .failed_restore
96
97 ; find the bit in question
98 sub xDI, 4 ; one step back.
99%if ARCH_BITS == 16
100 movzx edi, di
101 mov eax, [es:xDI]
102%else
103 mov eax, [xDI]
104%endif
105 sub xDI, xDX
106 shl edi, 3 ; calc bit offset.
107
108 bsf ecx, eax
109 jz .failed_restore ; race paranoia
110 add ecx, edi
111 mov eax, ecx
112
113 ; return success
114 pop xDI
115%if ARCH_BITS == 16
116 mov edx, eax
117 shr edx, 16
118 leave
119%endif
120 ret
121
122 ; failure
123 ;}
124 ;return -1;
125.failed_restore:
126 pop xDI
127.failed:
128%if ARCH_BITS != 16
129 mov eax, 0ffffffffh
130%else
131 mov ax, 0ffffh
132 mov dx, ax
133 leave
134%endif
135 ret
136ENDPROC ASMBitFirstSet
137
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