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 __umoddi3(du_int a, du_int b); 8 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. 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(__umoddi3) 26 27 pushl %ebx 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]. 31 32 // High word of b is known to be non-zero on this branch 33 34 movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 35 36 shrl %cl, %eax // Practically, this means that bhi is given by: 37 shrl %eax // 38 notl %ecx // bhi = (high word of b) << (31 - i) | 39 shll %cl, %ebx // (low word of b) >> (1 + i) 40 orl %eax, %ebx // 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. 44 jae 2f 45 46 // High word of a is greater than or equal to (b >> (1 + i)) on this branch 47 48 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 49 50 pushl %edi 51 notl %ecx 52 shrl %eax 53 shrl %cl, %eax // q = qs >> (1 + i) 54 movl %eax, %edi 55 mull 20(%esp) // q*blo 56 movl 12(%esp), %ebx 57 movl 16(%esp), %ecx // ECX:EBX = a 58 subl %eax, %ebx 59 sbbl %edx, %ecx // ECX:EBX = a - q*blo 60 movl 24(%esp), %eax 61 imull %edi, %eax // q*bhi 62 subl %eax, %ecx // ECX:EBX = a - q*b 63 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 671: movl %ebx, %eax 68 movl %ecx, %edx 69 70 popl %edi 71 popl %ebx 72 retl 73 74 752: // High word of a is greater than or equal to (b >> (1 + i)) on this branch 76 77 subl %ebx, %edx // subtract bhi from ahi so that divide will not 78 divl %ebx // overflow, and find q and r such that 79 // 80 // ahi:alo = (1:q)*bhi + r 81 // 82 // Note that q is a number in (31-i).(1+i) 83 // fix point. 84 85 pushl %edi 86 notl %ecx 87 shrl %eax 88 orl $0x80000000, %eax 89 shrl %cl, %eax // q = (1:qs) >> (1 + i) 90 movl %eax, %edi 91 mull 20(%esp) // q*blo 92 movl 12(%esp), %ebx 93 movl 16(%esp), %ecx // ECX:EBX = a 94 subl %eax, %ebx 95 sbbl %edx, %ecx // ECX:EBX = a - q*blo 96 movl 24(%esp), %eax 97 imull %edi, %eax // q*bhi 98 subl %eax, %ecx // ECX:EBX = a - q*b 99 100 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 1033: movl %ebx, %eax 104 movl %ecx, %edx 105 106 popl %edi 107 popl %ebx 108 retl 109 110 111 1129: // High word of b is zero on this branch 113 114 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 117 divl %ecx // 118 movl %eax, %ebx // 119 movl 8(%esp), %eax // Find rlo such that 120 divl %ecx // 121 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b 122 popl %ebx // 123 xorl %edx, %edx // and return 0:rlo 124 retl // 125END_COMPILERRT_FUNCTION(__umoddi3) 126 127#endif // __i386__ 128 129NO_EXEC_STACK_DIRECTIVE 130 131