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 __divdi3(di_int a, di_int b); 8 9// result = 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// Stephen Canon, December 2008 19 20#ifdef __i386__ 21 22.text 23.balign 4 24DEFINE_COMPILERRT_FUNCTION(__divdi3) 25 26// This is currently implemented by wrapping the unsigned divide up in an absolute 27// value, then restoring the correct sign at the end of the computation. This could 28// 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 movl %ecx, %esi // set aside sign of b 42 43 movl 12(%esp), %edx // high word of b 44 movl 8(%esp), %eax // low word of b 45 movl %edx, %ecx 46 sarl $31, %ecx // (a < 0) ? -1 : 0 47 xorl %ecx, %eax 48 xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a 49 subl %ecx, %eax 50 sbbl %ecx, %edx // EDX:EAX = abs(a) 51 movl %edx, 12(%esp) 52 movl %eax, 8(%esp) // store abs(a) back to stack 53 xorl %ecx, %esi // sign of result = (sign of a) ^ (sign of b) 54 55 pushl %ebx 56 movl 24(%esp), %ebx // Find the index i of the leading bit in b. 57 bsrl %ebx, %ecx // If the high word of b is zero, jump to 58 jz 9f // the code to handle that special case [9]. 59 60 // High word of b is known to be non-zero on this branch 61 62 movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 63 64 shrl %cl, %eax // Practically, this means that bhi is given by: 65 shrl %eax // 66 notl %ecx // bhi = (high word of b) << (31 - i) | 67 shll %cl, %ebx // (low word of b) >> (1 + i) 68 orl %eax, %ebx // 69 movl 16(%esp), %edx // Load the high and low words of a, and jump 70 movl 12(%esp), %eax // to [1] if the high word is larger than bhi 71 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 72 jae 1f 73 74 // High word of a is greater than or equal to (b >> (1 + i)) on this branch 75 76 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 77 78 pushl %edi 79 notl %ecx 80 shrl %eax 81 shrl %cl, %eax // q = qs >> (1 + i) 82 movl %eax, %edi 83 mull 24(%esp) // q*blo 84 movl 16(%esp), %ebx 85 movl 20(%esp), %ecx // ECX:EBX = a 86 subl %eax, %ebx 87 sbbl %edx, %ecx // ECX:EBX = a - q*blo 88 movl 28(%esp), %eax 89 imull %edi, %eax // q*bhi 90 subl %eax, %ecx // ECX:EBX = a - q*b 91 sbbl $0, %edi // decrement q if remainder is negative 92 xorl %edx, %edx 93 movl %edi, %eax 94 95 addl %esi, %eax // Restore correct sign to result 96 adcl %esi, %edx 97 xorl %esi, %eax 98 xorl %esi, %edx 99 popl %edi // Restore callee-save registers 100 popl %ebx 101 popl %esi 102 retl // Return 103 104 1051: // High word of a is greater than or equal to (b >> (1 + i)) on this branch 106 107 subl %ebx, %edx // subtract bhi from ahi so that divide will not 108 divl %ebx // overflow, and find q and r such that 109 // 110 // ahi:alo = (1:q)*bhi + r 111 // 112 // Note that q is a number in (31-i).(1+i) 113 // fix point. 114 115 pushl %edi 116 notl %ecx 117 shrl %eax 118 orl $0x80000000, %eax 119 shrl %cl, %eax // q = (1:qs) >> (1 + i) 120 movl %eax, %edi 121 mull 24(%esp) // q*blo 122 movl 16(%esp), %ebx 123 movl 20(%esp), %ecx // ECX:EBX = a 124 subl %eax, %ebx 125 sbbl %edx, %ecx // ECX:EBX = a - q*blo 126 movl 28(%esp), %eax 127 imull %edi, %eax // q*bhi 128 subl %eax, %ecx // ECX:EBX = a - q*b 129 sbbl $0, %edi // decrement q if remainder is negative 130 xorl %edx, %edx 131 movl %edi, %eax 132 133 addl %esi, %eax // Restore correct sign to result 134 adcl %esi, %edx 135 xorl %esi, %eax 136 xorl %esi, %edx 137 popl %edi // Restore callee-save registers 138 popl %ebx 139 popl %esi 140 retl // Return 141 142 1439: // High word of b is zero on this branch 144 145 movl 16(%esp), %eax // Find qhi and rhi such that 146 movl 20(%esp), %ecx // 147 xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b 148 divl %ecx // 149 movl %eax, %ebx // 150 movl 12(%esp), %eax // Find qlo such that 151 divl %ecx // 152 movl %ebx, %edx // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b 153 154 addl %esi, %eax // Restore correct sign to result 155 adcl %esi, %edx 156 xorl %esi, %eax 157 xorl %esi, %edx 158 popl %ebx // Restore callee-save registers 159 popl %esi 160 retl // Return 161END_COMPILERRT_FUNCTION(__divdi3) 162 163#endif // __i386__ 164 165NO_EXEC_STACK_DIRECTIVE 166 167