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
5 #include "../assembly.h"
7 // du_int __umoddi3(du_int a, du_int b);
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.
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.
19 // Stephen Canon, December 2008
25 DEFINE_COMPILERRT_FUNCTION(__umoddi3)
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].
32 // High word of b is known to be non-zero on this branch
34 movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
36 shrl %cl, %eax // Practically, this means that bhi is given by:
38 notl %ecx // bhi = (high word of b) << (31 - i) |
39 shll %cl, %ebx // (low word of b) >> (1 + i)
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.
46 // High word of a is greater than or equal to (b >> (1 + i)) on this branch
48 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
53 shrl %cl, %eax // q = qs >> (1 + i)
55 mull 20(%esp) // q*blo
57 movl 16(%esp), %ecx // ECX:EBX = a
59 sbbl %edx, %ecx // ECX:EBX = a - q*blo
61 imull %edi, %eax // q*bhi
62 subl %eax, %ecx // ECX:EBX = a - q*b
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
75 2: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
77 subl %ebx, %edx // subtract bhi from ahi so that divide will not
78 divl %ebx // overflow, and find q and r such that
80 // ahi:alo = (1:q)*bhi + r
82 // Note that q is a number in (31-i).(1+i)
89 shrl %cl, %eax // q = (1:qs) >> (1 + i)
91 mull 20(%esp) // q*blo
93 movl 16(%esp), %ecx // ECX:EBX = a
95 sbbl %edx, %ecx // ECX:EBX = a - q*blo
97 imull %edi, %eax // q*bhi
98 subl %eax, %ecx // ECX:EBX = a - q*b
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
112 9: // High word of b is zero on this branch
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
119 movl 8(%esp), %eax // Find rlo such that
121 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b
123 xorl %edx, %edx // and return 0:rlo
125 END_COMPILERRT_FUNCTION(__umoddi3)
129 NO_EXEC_STACK_DIRECTIVE