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