VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitFirstClear.asm@ 78365

Last change on this file since 78365 was 76553, checked in by vboxsync, 6 years ago

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1; $Id: ASMBitFirstClear.asm 76553 2019-01-01 01:45:53Z vboxsync $
2;; @file
3; IPRT - ASMBitFirstClear().
4;
5
6;
7; Copyright (C) 2006-2019 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 clear bit in a bitmap.
37;
38; @returns (32/64:eax, 16:ax+dx) Index of the first zero bit.
39; @returns (32/64:eax, 16:ax+dx) -1 if no clear bit was found.
40; @param msc:rcx gcc:rdi pvBitmap Pointer to the bitmap.
41; @param msc:edx gcc:rsi cBits The number of bits in the bitmap. Multiple of 32.
42;
43BEGINPROC_EXPORTED ASMBitFirstClear
44 ;
45 ; if (cBits)
46 ; Put cBits in ecx first.
47 ;
48%if ARCH_BITS == 64
49 %ifdef ASM_CALL64_GCC
50 mov ecx, esi
51 %else
52 xchg rcx, rdx ; rdx=pvDst, ecx=cBits
53 %endif
54%elif ARCH_BITS == 32
55 mov ecx, [esp + 4 + 4]
56%elif ARCH_BITS == 16
57 push bp
58 mov bp, sp
59 mov ecx, [bp + 4 + 4]
60%endif
61 or ecx, ecx
62 jz short .failed
63 ;{
64 push xDI
65
66 ; asm {...}
67%if ARCH_BITS == 64
68 %ifdef ASM_CALL64_GCC
69 ; rdi = start of scasd - already done
70 %else
71 mov rdi, rdx ; rdi = start of scasd (Note! xchg rdx,rcx above)
72 %endif
73%elif ARCH_BITS == 32
74 mov edi, [esp + 8]
75%elif ARCH_BITS == 16
76 mov ax, [bp + 4 + 2]
77 mov di, [bp + 4]
78 mov es, ax ; es is volatile, no need to save.
79%endif
80 add ecx, 31 ; 32 bit aligned
81 shr ecx, 5 ; number of dwords to scan.
82 mov xDX, xDI ; xDX = saved pvBitmap
83 mov eax, 0ffffffffh
84 repe scasd ; Scan for the first dword with any clear bit.
85 je .failed_restore
86
87 ; find the bit in question
88 sub xDI, 4 ; one step back.
89%if ARCH_BITS == 16
90 movzx edi, di
91 xor eax, [es:xDI] ; eax = NOT [rdi]
92%else
93 xor eax, [xDI] ; eax = NOT [rdi]
94%endif
95 sub xDI, xDX
96 shl edi, 3 ; calc bit offset.
97
98 bsf ecx, eax
99 jz .failed_restore ; race paranoia
100 add ecx, edi
101 mov eax, ecx
102
103 ; return success
104 pop xDI
105%if ARCH_BITS == 16
106 mov edx, eax
107 shr edx, 16
108 leave
109%endif
110 ret
111
112 ; failure
113 ;}
114 ;return -1;
115.failed_restore:
116 pop xDI
117.failed:
118%if ARCH_BITS != 16
119 mov eax, 0ffffffffh
120%else
121 mov ax, 0ffffh
122 mov dx, ax
123 leave
124%endif
125 ret
126ENDPROC ASMBitFirstClear
127
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