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 __udivdi3(du_int a, du_int b); 7 8 // result = 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 // Stephen Canon, December 2008 18 19 #ifdef __i386__ 20 21 .text 22 .balign 4 23 DEFINE_COMPILERRT_FUNCTION(__udivdi3) 24 25 pushl %ebx 26 movl 20(%esp), %ebx // Find the index i of the leading bit in b. 27 bsrl %ebx, %ecx // If the high word of b is zero, jump to 28 jz 9f // the code to handle that special case [9]. 29 30 /* High word of b is known to be non-zero on this branch */ 31 32 movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 33 34 shrl %cl, %eax // Practically, this means that bhi is given by: 35 shrl %eax // 36 notl %ecx // bhi = (high word of b) << (31 - i) | 37 shll %cl, %ebx // (low word of b) >> (1 + i) 38 orl %eax, %ebx // 39 movl 12(%esp), %edx // Load the high and low words of a, and jump 40 movl 8(%esp), %eax // to [1] if the high word is larger than bhi 41 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 42 jae 1f 43 44 /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 45 46 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 47 48 pushl %edi 49 notl %ecx 50 shrl %eax 51 shrl %cl, %eax // q = qs >> (1 + i) 52 movl %eax, %edi 53 mull 20(%esp) // q*blo 54 movl 12(%esp), %ebx 55 movl 16(%esp), %ecx // ECX:EBX = a 56 subl %eax, %ebx 57 sbbl %edx, %ecx // ECX:EBX = a - q*blo 58 movl 24(%esp), %eax 59 imull %edi, %eax // q*bhi 60 subl %eax, %ecx // ECX:EBX = a - q*b 61 sbbl $0, %edi // decrement q if remainder is negative 62 xorl %edx, %edx 63 movl %edi, %eax 64 popl %edi 65 popl %ebx 66 retl 67 68 69 1: /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 70 71 subl %ebx, %edx // subtract bhi from ahi so that divide will not 72 divl %ebx // overflow, and find q and r such that 73 // 74 // ahi:alo = (1:q)*bhi + r 75 // 76 // Note that q is a number in (31-i).(1+i) 77 // fix point. 78 79 pushl %edi 80 notl %ecx 81 shrl %eax 82 orl $0x80000000, %eax 83 shrl %cl, %eax // q = (1:qs) >> (1 + i) 84 movl %eax, %edi 85 mull 20(%esp) // q*blo 86 movl 12(%esp), %ebx 87 movl 16(%esp), %ecx // ECX:EBX = a 88 subl %eax, %ebx 89 sbbl %edx, %ecx // ECX:EBX = a - q*blo 90 movl 24(%esp), %eax 91 imull %edi, %eax // q*bhi 92 subl %eax, %ecx // ECX:EBX = a - q*b 93 sbbl $0, %edi // decrement q if remainder is negative 94 xorl %edx, %edx 95 movl %edi, %eax 96 popl %edi 97 popl %ebx 98 retl 99 100 101 9: /* High word of b is zero on this branch */ 102 103 movl 12(%esp), %eax // Find qhi and rhi such that 104 movl 16(%esp), %ecx // 105 xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b 106 divl %ecx // 107 movl %eax, %ebx // 108 movl 8(%esp), %eax // Find qlo such that 109 divl %ecx // 110 movl %ebx, %edx // rhi:alo = qlo*b + rlo with 0 rlo < b 111 popl %ebx // 112 retl // and return qhi:qlo 113 END_COMPILERRT_FUNCTION(__udivdi3) 114 115 #endif // __i386__ 116 117 NO_EXEC_STACK_DIRECTIVE 118 119
