1 // This file is dual licensed under the MIT and the University of Illinois Open 2 // Source Licenses. See LICENSE.TXT for details. 3 4 #include "../assembly.h" 5 6 // du_int __umoddi3(du_int a, du_int b); 7 8 // result = remainder of a / b. 9 // both inputs and the output are 64-bit unsigned integers. 10 // This will do whatever the underlying hardware is set to do on division by zero. 11 // No other exceptions are generated, as the divide cannot overflow. 12 // 13 // This is targeted at 32-bit x86 *only*, as this can be done directly in hardware 14 // on x86_64. The performance goal is ~40 cycles per divide, which is faster than 15 // currently possible via simulation of integer divides on the x87 unit. 16 // 17 18 // Stephen Canon, December 2008 19 20 #ifdef __i386__ 21 22 .text 23 .balign 4 24 DEFINE_COMPILERRT_FUNCTION(__umoddi3) 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 [2] if the high word is larger than bhi 42 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 43 jae 2f 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 63 jnc 1f // if positive, this is the result. 64 addl 20(%esp), %ebx // otherwise 65 adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 66 1: movl %ebx, %eax 67 movl %ecx, %edx 68 69 popl %edi 70 popl %ebx 71 retl 72 73 74 2: /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 75 76 subl %ebx, %edx // subtract bhi from ahi so that divide will not 77 divl %ebx // overflow, and find q and r such that 78 // 79 // ahi:alo = (1:q)*bhi + r 80 // 81 // Note that q is a number in (31-i).(1+i) 82 // fix point. 83 84 pushl %edi 85 notl %ecx 86 shrl %eax 87 orl $0x80000000, %eax 88 shrl %cl, %eax // q = (1:qs) >> (1 + i) 89 movl %eax, %edi 90 mull 20(%esp) // q*blo 91 movl 12(%esp), %ebx 92 movl 16(%esp), %ecx // ECX:EBX = a 93 subl %eax, %ebx 94 sbbl %edx, %ecx // ECX:EBX = a - q*blo 95 movl 24(%esp), %eax 96 imull %edi, %eax // q*bhi 97 subl %eax, %ecx // ECX:EBX = a - q*b 98 99 jnc 3f // if positive, this is the result. 100 addl 20(%esp), %ebx // otherwise 101 adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 102 3: movl %ebx, %eax 103 movl %ecx, %edx 104 105 popl %edi 106 popl %ebx 107 retl 108 109 110 111 9: /* High word of b is zero on this branch */ 112 113 movl 12(%esp), %eax // Find qhi and rhi such that 114 movl 16(%esp), %ecx // 115 xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b 116 divl %ecx // 117 movl %eax, %ebx // 118 movl 8(%esp), %eax // Find rlo such that 119 divl %ecx // 120 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 rlo < b 121 popl %ebx // 122 xorl %edx, %edx // and return 0:rlo 123 retl // 124 END_COMPILERRT_FUNCTION(__umoddi3) 125 126 #endif // __i386__ 127
