1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
; $Id$
;; @file
; IPRT - ASMBitNextClear().
;
;
; Copyright (C) 2006-2017 Oracle Corporation
;
; This file is part of VirtualBox Open Source Edition (OSE), as
; available from http://www.virtualbox.org. This file is free software;
; you can redistribute it and/or modify it under the terms of the GNU
; General Public License (GPL) as published by the Free Software
; Foundation, in version 2 as it comes in the "COPYING" file of the
; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
; VirtualBox OSE distribution, in which case the provisions of the
; CDDL are applicable instead of those of the GPL.
;
; You may elect to license modified versions of this file under the
; terms and conditions of either the GPL or the CDDL or both.
;
;*******************************************************************************
;* Header Files *
;*******************************************************************************
%include "iprt/asmdefs.mac"
BEGINCODE
;;
; Finds the next clear bit in a bitmap.
;
; @returns (32/64:eax, 16:ax+dx) Index of the first zero bit.
; @returns (32/64:eax, 16:ax+dx) -1 if no clear bit was found.
; @param msc:rcx gcc:rdi pvBitmap Pointer to the bitmap.
; @param msc:edx gcc:rsi cBits The number of bits in the bitmap. Multiple of 32.
; @param msc:r8d gcc:rcx iBitPrev The previous bit, start searching after it.
;
; @remarks Not quite sure how much sense it makes to do this in assembly, but
; it started out with the ASMBit* API, so that's why we still have it.
;
BEGINPROC_EXPORTED ASMBitNextClear
%if ARCH_BITS == 16
push bp
mov bp, sp
%endif
push xDI
;
; Align input registers: rdi=pvBitmap, ecx=iPrevBit
;
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
; ecx = iBitPrev param, rdi=pvBitmap param.
%else
mov rdi, rcx ; rdi=pvBits
mov ecx, r8d ; ecx=iPrevBit
mov r8d, edx ; r8d=cBits (saved for .scan_dwords)
%endif
mov r9, rdi ; Save rdi for bit calculation.
%elif ARCH_BITS == 32
mov edi, [esp + 8] ; edi=pvBits
mov ecx, [esp + 8 + 8] ; ecx=iPrevBit
%elif ARCH_BITS == 16
les di, [bp + 4] ; es:di=pvBits
mov ecx, [bp + 4 + 8] ; ecx=iPrevBit
%endif
;
; If iPrevBit and iPrevBit + 1 are in the same dword, inspect it for further bits.
;
inc ecx
mov eax, ecx
shr eax, 5
shl eax, 2 ; eax=byte offset into bitmap of current dword.
add xDI, xAX ; xDI=current dword address (of iPrevBit + 1).
and ecx, 31
jz .scan_dwords
%if ARCH_BITS == 16
mov edx, [es:di]
%else
mov edx, [xDI]
%endif
not edx ; edx = inverted current dword
shr edx, cl ; Shift out bits that we have searched.
jz .next_dword ; If zero, nothing to find. Go rep scasd.
shl edx, cl ; Shift it back so bsf will return the right index.
bsf edx, edx ; edx=index of first clear bit
shl eax, 3 ; Turn eax back into a bit offset of the current dword.
add eax, edx ; eax=bit offset
.return:
pop xDI
%if ARCH_BITS == 16
mov edx, eax
shr edx, 16
leave
%endif
ret
;
; Do dword scan.
;
; Skip empty dword.
.next_dword:
add xDI, 4 ; Skip the empty dword.
add eax, 4
.scan_dwords:
; First load and align bit count.
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
mov ecx, esi
%else
mov ecx, r8d
%endif
%elif ARCH_BITS == 32
mov ecx, [esp + 8 + 4]
%elif ARCH_BITS == 16
mov ecx, [bp + 4 + 4]
%endif
add ecx, 31
shr ecx, 5 ; ecx=bitmap size in dwords.
; Adjust ecx to how many dwords there are left to scan. (eax = current byte offset)
shr eax, 2 ; eax=current dword offset.
sub ecx, eax
jbe .return_failure
; Do the scanning.
cld
mov eax, 0ffffffffh
repe scasd
je .return_failure
; Find the bit in question.
sub xDI, 4 ; One step back.
%if ARCH_BITS == 16
movzx edi, di
xor eax, [es:xDI]
%else
xor eax, [xDI]
%endif
bsf eax, eax
jz .return_failure ; race paranoia
; Calc the bit offset.
%if ARCH_BITS == 16
sub di, [bp + 4]
movzx edi, di
%elif ARCH_BITS == 32
sub xDI, [esp + 8]
%elif ARCH_BITS == 64
sub xDI, r9
%endif
shl edi, 3 ; edi=bit offset of current dword.
add eax, edi
jmp .return
.return_failure:
mov eax, 0ffffffffh
jmp .return
ENDPROC ASMBitNextClear
|
