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
|
;***
;ulldiv.asm - unsigned long divide routine
;
; Copyright (c) Microsoft Corporation. All rights reserved.
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
;Purpose:
; defines the unsigned long divide routine
; __aulldiv
;
;Original Implemenation: MSVC 14.29.30133
;
;*******************************************************************************
.686
.model flat,C
.code
;***
;ulldiv - unsigned long divide
;
;Purpose:
; Does a unsigned long divide of the arguments. Arguments are
; not changed.
;
;Entry:
; Arguments are passed on the stack:
; 1st pushed: divisor (QWORD)
; 2nd pushed: dividend (QWORD)
;
;Exit:
; EDX:EAX contains the quotient (dividend/divisor)
; NOTE: this routine removes the parameters from the stack.
;
;Uses:
; ECX
;
;Exceptions:
;
;*******************************************************************************
_aulldiv PROC NEAR
HIWORD EQU [4] ;
LOWORD EQU [0]
push ebx
push esi
; Set up the local stack and save the index registers. When this is done
; the stack frame will look as follows (assuming that the expression a/b will
; generate a call to uldiv(a, b)):
;
; -----------------
; | |
; |---------------|
; | |
; |--divisor (b)--|
; | |
; |---------------|
; | |
; |--dividend (a)-|
; | |
; |---------------|
; | return addr** |
; |---------------|
; | EBX |
; |---------------|
; ESP---->| ESI |
; -----------------
;
DVND equ [esp + 12] ; stack address of dividend (a)
DVSR equ [esp + 20] ; stack address of divisor (b)
;
; Now do the divide. First look to see if the divisor is less than 4194304K.
; If so, then we can use a simple algorithm with word divides, otherwise
; things get a little more complex.
;
mov eax,HIWORD(DVSR) ; check to see if divisor < 4194304K
or eax,eax
jnz short L1 ; nope, gotta do this the hard way
mov ecx,LOWORD(DVSR) ; load divisor
mov eax,HIWORD(DVND) ; load high word of dividend
xor edx,edx
div ecx ; get high order bits of quotient
mov ebx,eax ; save high bits of quotient
mov eax,LOWORD(DVND) ; edx:eax <- remainder:lo word of dividend
div ecx ; get low order bits of quotient
mov edx,ebx ; edx:eax <- quotient hi:quotient lo
jmp short L2 ; restore stack and return
;
; Here we do it the hard way. Remember, eax contains DVSRHI
;
L1:
mov ecx,eax ; ecx:ebx <- divisor
mov ebx,LOWORD(DVSR)
mov edx,HIWORD(DVND) ; edx:eax <- dividend
mov eax,LOWORD(DVND)
L3:
shr ecx,1 ; shift divisor right one bit; hi bit <- 0
rcr ebx,1
shr edx,1 ; shift dividend right one bit; hi bit <- 0
rcr eax,1
or ecx,ecx
jnz short L3 ; loop until divisor < 4194304K
div ebx ; now divide, ignore remainder
mov esi,eax ; save quotient
;
; We may be off by one, so to check, we will multiply the quotient
; by the divisor and check the result against the original dividend
; Note that we must also check for overflow, which can occur if the
; dividend is close to 2**64 and the quotient is off by 1.
;
mul dword ptr HIWORD(DVSR) ; QUOT * HIWORD(DVSR)
mov ecx,eax
mov eax,LOWORD(DVSR)
mul esi ; QUOT * LOWORD(DVSR)
add edx,ecx ; EDX:EAX = QUOT * DVSR
jc short L4 ; carry means Quotient is off by 1
;
; do long compare here between original dividend and the result of the
; multiply in edx:eax. If original is larger or equal, we are ok, otherwise
; subtract one (1) from the quotient.
;
cmp edx,HIWORD(DVND) ; compare hi words of result and original
ja short L4 ; if result > original, do subtract
jb short L5 ; if result < original, we are ok
cmp eax,LOWORD(DVND) ; hi words are equal, compare lo words
jbe short L5 ; if less or equal we are ok, else subtract
L4:
dec esi ; subtract 1 from quotient
L5:
xor edx,edx ; edx:eax <- quotient
mov eax,esi
;
; Just the cleanup left to do. edx:eax contains the quotient.
; Restore the saved registers and return.
;
L2:
pop esi
pop ebx
ret 16
_aulldiv ENDP
end
|
