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 __udivdi3(du_int a, du_int b);
8
9// result = 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// Stephen Canon, December 2008
19
20#ifdef __i386__
21
22.text
23.balign 4
24DEFINE_COMPILERRT_FUNCTION(__udivdi3)
25
26 pushl %ebx
27 movl 20(%esp), %ebx // Find the index i of the leading bit in b.
28 bsrl %ebx, %ecx // If the high word of b is zero, jump to
29 jz 9f // the code to handle that special case [9].
30
31 // High word of b is known to be non-zero on this branch
32
33 movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
34
35 shrl %cl, %eax // Practically, this means that bhi is given by:
36 shrl %eax //
37 notl %ecx // bhi = (high word of b) << (31 - i) |
38 shll %cl, %ebx // (low word of b) >> (1 + i)
39 orl %eax, %ebx //
40 movl 12(%esp), %edx // Load the high and low words of a, and jump
41 movl 8(%esp), %eax // to [1] if the high word is larger than bhi
42 cmpl %ebx, %edx // to avoid overflowing the upcoming divide.
43 jae 1f
44
45 // High word of a is greater than or equal to (b >> (1 + i)) on this branch
46
47 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
48
49 pushl %edi
50 notl %ecx
51 shrl %eax
52 shrl %cl, %eax // q = qs >> (1 + i)
53 movl %eax, %edi
54 mull 20(%esp) // q*blo
55 movl 12(%esp), %ebx
56 movl 16(%esp), %ecx // ECX:EBX = a
57 subl %eax, %ebx
58 sbbl %edx, %ecx // ECX:EBX = a - q*blo
59 movl 24(%esp), %eax
60 imull %edi, %eax // q*bhi
61 subl %eax, %ecx // ECX:EBX = a - q*b
62 sbbl $0, %edi // decrement q if remainder is negative
63 xorl %edx, %edx
64 movl %edi, %eax
65 popl %edi
66 popl %ebx
67 retl
68
69
701: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
71
72 subl %ebx, %edx // subtract bhi from ahi so that divide will not
73 divl %ebx // overflow, and find q and r such that
74 //
75 // ahi:alo = (1:q)*bhi + r
76 //
77 // Note that q is a number in (31-i).(1+i)
78 // fix point.
79
80 pushl %edi
81 notl %ecx
82 shrl %eax
83 orl $0x80000000, %eax
84 shrl %cl, %eax // q = (1:qs) >> (1 + i)
85 movl %eax, %edi
86 mull 20(%esp) // q*blo
87 movl 12(%esp), %ebx
88 movl 16(%esp), %ecx // ECX:EBX = a
89 subl %eax, %ebx
90 sbbl %edx, %ecx // ECX:EBX = a - q*blo
91 movl 24(%esp), %eax
92 imull %edi, %eax // q*bhi
93 subl %eax, %ecx // ECX:EBX = a - q*b
94 sbbl $0, %edi // decrement q if remainder is negative
95 xorl %edx, %edx
96 movl %edi, %eax
97 popl %edi
98 popl %ebx
99 retl
100
101
1029: // High word of b is zero on this branch
103
104 movl 12(%esp), %eax // Find qhi and rhi such that
105 movl 16(%esp), %ecx //
106 xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b
107 divl %ecx //
108 movl %eax, %ebx //
109 movl 8(%esp), %eax // Find qlo such that
110 divl %ecx //
111 movl %ebx, %edx // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b
112 popl %ebx //
113 retl // and return qhi:qlo
114END_COMPILERRT_FUNCTION(__udivdi3)
115
116#endif // __i386__
117
118NO_EXEC_STACK_DIRECTIVE
119
120

source code of compiler-rt/lib/builtins/i386/udivdi3.S