1// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
2// See https://llvm.org/LICENSE.txt for license information.
3// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
4
5#include "../assembly.h"
6
7// du_int __umoddi3(du_int a, du_int b);
8
9// result = remainder of a / b.
10// both inputs and the output are 64-bit unsigned integers.
11// This will do whatever the underlying hardware is set to do on division by zero.
12// No other exceptions are generated, as the divide cannot overflow.
13//
14// This is targeted at 32-bit x86 *only*, as this can be done directly in hardware
15// on x86_64. The performance goal is ~40 cycles per divide, which is faster than
16// currently possible via simulation of integer divides on the x87 unit.
17//
18
19// Stephen Canon, December 2008
20
21#ifdef __i386__
22
23.text
24.balign 4
25DEFINE_COMPILERRT_FUNCTION(__umoddi3)
26
27 pushl %ebx
28 movl 20(%esp), %ebx // Find the index i of the leading bit in b.
29 bsrl %ebx, %ecx // If the high word of b is zero, jump to
30 jz 9f // the code to handle that special case [9].
31
32 // High word of b is known to be non-zero on this branch
33
34 movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
35
36 shrl %cl, %eax // Practically, this means that bhi is given by:
37 shrl %eax //
38 notl %ecx // bhi = (high word of b) << (31 - i) |
39 shll %cl, %ebx // (low word of b) >> (1 + i)
40 orl %eax, %ebx //
41 movl 12(%esp), %edx // Load the high and low words of a, and jump
42 movl 8(%esp), %eax // to [2] if the high word is larger than bhi
43 cmpl %ebx, %edx // to avoid overflowing the upcoming divide.
44 jae 2f
45
46 // High word of a is greater than or equal to (b >> (1 + i)) on this branch
47
48 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
49
50 pushl %edi
51 notl %ecx
52 shrl %eax
53 shrl %cl, %eax // q = qs >> (1 + i)
54 movl %eax, %edi
55 mull 20(%esp) // q*blo
56 movl 12(%esp), %ebx
57 movl 16(%esp), %ecx // ECX:EBX = a
58 subl %eax, %ebx
59 sbbl %edx, %ecx // ECX:EBX = a - q*blo
60 movl 24(%esp), %eax
61 imull %edi, %eax // q*bhi
62 subl %eax, %ecx // ECX:EBX = a - q*b
63
64 jnc 1f // if positive, this is the result.
65 addl 20(%esp), %ebx // otherwise
66 adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
671: movl %ebx, %eax
68 movl %ecx, %edx
69
70 popl %edi
71 popl %ebx
72 retl
73
74
752: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
76
77 subl %ebx, %edx // subtract bhi from ahi so that divide will not
78 divl %ebx // overflow, and find q and r such that
79 //
80 // ahi:alo = (1:q)*bhi + r
81 //
82 // Note that q is a number in (31-i).(1+i)
83 // fix point.
84
85 pushl %edi
86 notl %ecx
87 shrl %eax
88 orl $0x80000000, %eax
89 shrl %cl, %eax // q = (1:qs) >> (1 + i)
90 movl %eax, %edi
91 mull 20(%esp) // q*blo
92 movl 12(%esp), %ebx
93 movl 16(%esp), %ecx // ECX:EBX = a
94 subl %eax, %ebx
95 sbbl %edx, %ecx // ECX:EBX = a - q*blo
96 movl 24(%esp), %eax
97 imull %edi, %eax // q*bhi
98 subl %eax, %ecx // ECX:EBX = a - q*b
99
100 jnc 3f // if positive, this is the result.
101 addl 20(%esp), %ebx // otherwise
102 adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
1033: movl %ebx, %eax
104 movl %ecx, %edx
105
106 popl %edi
107 popl %ebx
108 retl
109
110
111
1129: // High word of b is zero on this branch
113
114 movl 12(%esp), %eax // Find qhi and rhi such that
115 movl 16(%esp), %ecx //
116 xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b
117 divl %ecx //
118 movl %eax, %ebx //
119 movl 8(%esp), %eax // Find rlo such that
120 divl %ecx //
121 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b
122 popl %ebx //
123 xorl %edx, %edx // and return 0:rlo
124 retl //
125END_COMPILERRT_FUNCTION(__umoddi3)
126
127#endif // __i386__
128
129NO_EXEC_STACK_DIRECTIVE
130
131

source code of compiler-rt/lib/builtins/i386/umoddi3.S