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
|
; $Id: __U4M.asm $
;; @file
; Compiler support routines.
;
;
; Copyright (C) 2012-2023 Oracle and/or its affiliates.
;
; This file is part of VirtualBox base platform packages, as
; available from https://www.virtualbox.org.
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation, in version 3 of the
; License.
;
; This program is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, see <https://www.gnu.org/licenses>.
;
; SPDX-License-Identifier: GPL-3.0-only
;
;*******************************************************************************
;* Exported Symbols *
;*******************************************************************************
public __U4M
; MASM (ML.EXE) is used for PXE and no longer understands the .8086 directive.
; WASM is used for the BIOS and understands it just fine.
ifdef __WASM__
.8086
endif
_TEXT segment public 'CODE' use16
assume cs:_TEXT
;;
; 32-bit unsigned multiplication.
;
; @param dx:ax Factor 1.
; @param cx:bx Factor 2.
; @returns dx:ax Result.
;
__U4M:
pushf
if VBOX_BIOS_CPU ge 80386
.386
push eax
push edx
push ecx
rol eax, 16
mov ax, dx
ror eax, 16
xor edx, edx
shr ecx, 16
mov cx, bx
mul ecx ; eax * ecx -> edx:eax
pop ecx
pop edx
ror eax, 16
mov dx, ax
add sp, 2
pop ax
rol eax, 16
ifdef __WASM__
.8086
endif
else
push si ; high result
push di ; low result
;
; dx:ax * cx:bx =
;-----------------------
; ax*bx
; + dx*bx ; only lower 16 bits relevant.
; + ax*cx ; ditto
; +dx*cx ; not relevant
; -------------
; = dx:ax
;
push ax ; stash the low factor 1 part for the 3rd multiplication.
mov di, dx ; stash the high factor 1 part for the 2nd multiplication.
; multiply the two low factor "digits": ax * bx
mul bx
mov si, dx
xchg di, ax ; save low result and loads high factor 1 into ax for the next step
; Multiply the low right "digit" by the high left one and add it to the high result part
mul bx
add si, ax
; Multiply the high right "digit" by the low left on and add it ot the high result part.
pop ax
mul cx
add si, ax
; Load the result.
mov dx, si
mov ax, di
pop di
pop si
endif
popf
ret
_TEXT ends
end
|
