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// di_int __moddi3(di_int a, di_int b); 8 9// result = remainder of a / b. 10// both inputs and the output are 64-bit signed 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(__moddi3) 26 27// This is currently implemented by wrapping the unsigned modulus up in an absolute 28// value. This could certainly be improved upon. 29 30 pushl %esi 31 movl 20(%esp), %edx // high word of b 32 movl 16(%esp), %eax // low word of b 33 movl %edx, %ecx 34 sarl $31, %ecx // (b < 0) ? -1 : 0 35 xorl %ecx, %eax 36 xorl %ecx, %edx // EDX:EAX = (b < 0) ? not(b) : b 37 subl %ecx, %eax 38 sbbl %ecx, %edx // EDX:EAX = abs(b) 39 movl %edx, 20(%esp) 40 movl %eax, 16(%esp) // store abs(b) back to stack 41 42 movl 12(%esp), %edx // high word of b 43 movl 8(%esp), %eax // low word of b 44 movl %edx, %ecx 45 sarl $31, %ecx // (a < 0) ? -1 : 0 46 xorl %ecx, %eax 47 xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a 48 subl %ecx, %eax 49 sbbl %ecx, %edx // EDX:EAX = abs(a) 50 movl %edx, 12(%esp) 51 movl %eax, 8(%esp) // store abs(a) back to stack 52 movl %ecx, %esi // set aside sign of a 53 54 pushl %ebx 55 movl 24(%esp), %ebx // Find the index i of the leading bit in b. 56 bsrl %ebx, %ecx // If the high word of b is zero, jump to 57 jz 9f // the code to handle that special case [9]. 58 59 // High word of b is known to be non-zero on this branch 60 61 movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 62 63 shrl %cl, %eax // Practically, this means that bhi is given by: 64 shrl %eax // 65 notl %ecx // bhi = (high word of b) << (31 - i) | 66 shll %cl, %ebx // (low word of b) >> (1 + i) 67 orl %eax, %ebx // 68 movl 16(%esp), %edx // Load the high and low words of a, and jump 69 movl 12(%esp), %eax // to [2] if the high word is larger than bhi 70 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 71 jae 2f 72 73 // High word of a is greater than or equal to (b >> (1 + i)) on this branch 74 75 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 76 77 pushl %edi 78 notl %ecx 79 shrl %eax 80 shrl %cl, %eax // q = qs >> (1 + i) 81 movl %eax, %edi 82 mull 24(%esp) // q*blo 83 movl 16(%esp), %ebx 84 movl 20(%esp), %ecx // ECX:EBX = a 85 subl %eax, %ebx 86 sbbl %edx, %ecx // ECX:EBX = a - q*blo 87 movl 28(%esp), %eax 88 imull %edi, %eax // q*bhi 89 subl %eax, %ecx // ECX:EBX = a - q*b 90 91 jnc 1f // if positive, this is the result. 92 addl 24(%esp), %ebx // otherwise 93 adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 941: movl %ebx, %eax 95 movl %ecx, %edx 96 97 addl %esi, %eax // Restore correct sign to result 98 adcl %esi, %edx 99 xorl %esi, %eax 100 xorl %esi, %edx 101 popl %edi // Restore callee-save registers 102 popl %ebx 103 popl %esi 104 retl // Return 105 1062: // High word of a is greater than or equal to (b >> (1 + i)) on this branch 107 108 subl %ebx, %edx // subtract bhi from ahi so that divide will not 109 divl %ebx // overflow, and find q and r such that 110 // 111 // ahi:alo = (1:q)*bhi + r 112 // 113 // Note that q is a number in (31-i).(1+i) 114 // fix point. 115 116 pushl %edi 117 notl %ecx 118 shrl %eax 119 orl $0x80000000, %eax 120 shrl %cl, %eax // q = (1:qs) >> (1 + i) 121 movl %eax, %edi 122 mull 24(%esp) // q*blo 123 movl 16(%esp), %ebx 124 movl 20(%esp), %ecx // ECX:EBX = a 125 subl %eax, %ebx 126 sbbl %edx, %ecx // ECX:EBX = a - q*blo 127 movl 28(%esp), %eax 128 imull %edi, %eax // q*bhi 129 subl %eax, %ecx // ECX:EBX = a - q*b 130 131 jnc 3f // if positive, this is the result. 132 addl 24(%esp), %ebx // otherwise 133 adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 1343: movl %ebx, %eax 135 movl %ecx, %edx 136 137 addl %esi, %eax // Restore correct sign to result 138 adcl %esi, %edx 139 xorl %esi, %eax 140 xorl %esi, %edx 141 popl %edi // Restore callee-save registers 142 popl %ebx 143 popl %esi 144 retl // Return 145 1469: // High word of b is zero on this branch 147 148 movl 16(%esp), %eax // Find qhi and rhi such that 149 movl 20(%esp), %ecx // 150 xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b 151 divl %ecx // 152 movl %eax, %ebx // 153 movl 12(%esp), %eax // Find rlo such that 154 divl %ecx // 155 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b 156 popl %ebx // 157 xorl %edx, %edx // and return 0:rlo 158 159 addl %esi, %eax // Restore correct sign to result 160 adcl %esi, %edx 161 xorl %esi, %eax 162 xorl %esi, %edx 163 popl %esi 164 retl // Return 165END_COMPILERRT_FUNCTION(__moddi3) 166 167#endif // __i386__ 168 169NO_EXEC_STACK_DIRECTIVE 170 171