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
|
; $Id: ASMBitFirstSet.asm $
;; @file
; IPRT - ASMBitFirstSet().
;
;
; Copyright (C) 2006-2020 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 first set 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 set 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.
;
BEGINPROC_EXPORTED ASMBitFirstSet
;
; if (cBits)
; Put cBits in ecx first.
;
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
mov ecx, esi
%else
xchg rcx, rdx ; rdx=pvDst, ecx=cBits
%endif
%elif ARCH_BITS == 32
mov ecx, [esp + 4 + 4]
%elif ARCH_BITS == 16
push bp
mov bp, sp
mov ecx, [bp + 4 + 4]
%endif
or ecx, ecx
jz short .failed
;{
push xDI
; asm {...}
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
; rdi = start of scasd - already done
%else
mov rdi, rdx ; rdi = start of scasd (Note! xchg rdx,rcx above)
%endif
%elif ARCH_BITS == 32
mov edi, [esp + 4]
%elif ARCH_BITS == 16
mov ax, [bp + 4 + 2]
mov di, [bp + 4]
mov es, ax ; es is volatile, no need to save.
%endif
add ecx, 31 ; 32 bit aligned
shr ecx, 5 ; number of dwords to scan.
mov xDX, xDI ; xDX = saved pvBitmap
xor eax, eax
repe scasd ; Scan for the first dword with any bit set.
je .failed_restore
; find the bit in question
sub xDI, 4 ; one step back.
%if ARCH_BITS == 16
movzx edi, di
mov eax, [es:xDI]
%else
mov eax, [xDI]
%endif
sub xDI, xDX
shl edi, 3 ; calc bit offset.
bsf ecx, eax
jz .failed_restore ; race paranoia
add ecx, edi
mov eax, ecx
; return success
pop xDI
%if ARCH_BITS == 16
mov edx, eax
shr edx, 16
leave
%endif
ret
; failure
;}
;return -1;
.failed_restore:
pop xDI
.failed:
%if ARCH_BITS != 16
mov eax, 0ffffffffh
%else
mov ax, 0ffffh
mov dx, ax
leave
%endif
ret
ENDPROC ASMBitFirstSet
|
