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
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "../assembly.h"
// di_int __moddi3(di_int a, di_int b);
// result = remainder of a / b.
// both inputs and the output are 64-bit signed integers.
// This will do whatever the underlying hardware is set to do on division by zero.
// No other exceptions are generated, as the divide cannot overflow.
//
// This is targeted at 32-bit x86 *only*, as this can be done directly in hardware
// on x86_64. The performance goal is ~40 cycles per divide, which is faster than
// currently possible via simulation of integer divides on the x87 unit.
//
// Stephen Canon, December 2008
#ifdef __i386__
.text
.balign 4
DEFINE_COMPILERRT_FUNCTION(__moddi3)
// This is currently implemented by wrapping the unsigned modulus up in an absolute
// value. This could certainly be improved upon.
pushl %esi
movl 20(%esp), %edx // high word of b
movl 16(%esp), %eax // low word of b
movl %edx, %ecx
sarl $31, %ecx // (b < 0) ? -1 : 0
xorl %ecx, %eax
xorl %ecx, %edx // EDX:EAX = (b < 0) ? not(b) : b
subl %ecx, %eax
sbbl %ecx, %edx // EDX:EAX = abs(b)
movl %edx, 20(%esp)
movl %eax, 16(%esp) // store abs(b) back to stack
movl 12(%esp), %edx // high word of b
movl 8(%esp), %eax // low word of b
movl %edx, %ecx
sarl $31, %ecx // (a < 0) ? -1 : 0
xorl %ecx, %eax
xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a
subl %ecx, %eax
sbbl %ecx, %edx // EDX:EAX = abs(a)
movl %edx, 12(%esp)
movl %eax, 8(%esp) // store abs(a) back to stack
movl %ecx, %esi // set aside sign of a
pushl %ebx
movl 24(%esp), %ebx // Find the index i of the leading bit in b.
bsrl %ebx, %ecx // If the high word of b is zero, jump to
jz 9f // the code to handle that special case [9].
// High word of b is known to be non-zero on this branch
movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
shrl %cl, %eax // Practically, this means that bhi is given by:
shrl %eax //
notl %ecx // bhi = (high word of b) << (31 - i) |
shll %cl, %ebx // (low word of b) >> (1 + i)
orl %eax, %ebx //
movl 16(%esp), %edx // Load the high and low words of a, and jump
movl 12(%esp), %eax // to [2] if the high word is larger than bhi
cmpl %ebx, %edx // to avoid overflowing the upcoming divide.
jae 2f
// High word of a is greater than or equal to (b >> (1 + i)) on this branch
divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
pushl %edi
notl %ecx
shrl %eax
shrl %cl, %eax // q = qs >> (1 + i)
movl %eax, %edi
mull 24(%esp) // q*blo
movl 16(%esp), %ebx
movl 20(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 28(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
jnc 1f // if positive, this is the result.
addl 24(%esp), %ebx // otherwise
adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
1: movl %ebx, %eax
movl %ecx, %edx
addl %esi, %eax // Restore correct sign to result
adcl %esi, %edx
xorl %esi, %eax
xorl %esi, %edx
popl %edi // Restore callee-save registers
popl %ebx
popl %esi
retl // Return
2: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
subl %ebx, %edx // subtract bhi from ahi so that divide will not
divl %ebx // overflow, and find q and r such that
//
// ahi:alo = (1:q)*bhi + r
//
// Note that q is a number in (31-i).(1+i)
// fix point.
pushl %edi
notl %ecx
shrl %eax
orl $0x80000000, %eax
shrl %cl, %eax // q = (1:qs) >> (1 + i)
movl %eax, %edi
mull 24(%esp) // q*blo
movl 16(%esp), %ebx
movl 20(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 28(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
jnc 3f // if positive, this is the result.
addl 24(%esp), %ebx // otherwise
adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
3: movl %ebx, %eax
movl %ecx, %edx
addl %esi, %eax // Restore correct sign to result
adcl %esi, %edx
xorl %esi, %eax
xorl %esi, %edx
popl %edi // Restore callee-save registers
popl %ebx
popl %esi
retl // Return
9: // High word of b is zero on this branch
movl 16(%esp), %eax // Find qhi and rhi such that
movl 20(%esp), %ecx //
xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b
divl %ecx //
movl %eax, %ebx //
movl 12(%esp), %eax // Find rlo such that
divl %ecx //
movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b
popl %ebx //
xorl %edx, %edx // and return 0:rlo
addl %esi, %eax // Restore correct sign to result
adcl %esi, %edx
xorl %esi, %eax
xorl %esi, %edx
popl %esi
retl // Return
END_COMPILERRT_FUNCTION(__moddi3)
#endif // __i386__
NO_EXEC_STACK_DIRECTIVE
|
