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 // di_int __divdi3(di_int a, di_int b); 7 8 // result = a / b. 9 // both inputs and the output are 64-bit signed 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 .align 4 23 DEFINE_COMPILERRT_FUNCTION(__divdi3) 24 25 /* This is currently implemented by wrapping the unsigned divide up in an absolute 26 value, then restoring the correct sign at the end of the computation. This could 27 certainly be improved upon. */ 28 29 pushl %esi 30 movl 20(%esp), %edx // high word of b 31 movl 16(%esp), %eax // low word of b 32 movl %edx, %ecx 33 sarl $31, %ecx // (b < 0) ? -1 : 0 34 xorl %ecx, %eax 35 xorl %ecx, %edx // EDX:EAX = (b < 0) ? not(b) : b 36 subl %ecx, %eax 37 sbbl %ecx, %edx // EDX:EAX = abs(b) 38 movl %edx, 20(%esp) 39 movl %eax, 16(%esp) // store abs(b) back to stack 40 movl %ecx, %esi // set aside sign of b 41 42 movl 12(%esp), %edx // high word of b 43 movl 8(%esp), %eax // low word of b 44 movl %edx, %ecx 45 sarl $31, %ecx // (a < 0) ? -1 : 0 46 xorl %ecx, %eax 47 xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a 48 subl %ecx, %eax 49 sbbl %ecx, %edx // EDX:EAX = abs(a) 50 movl %edx, 12(%esp) 51 movl %eax, 8(%esp) // store abs(a) back to stack 52 xorl %ecx, %esi // sign of result = (sign of a) ^ (sign of b) 53 54 pushl %ebx 55 movl 24(%esp), %ebx // Find the index i of the leading bit in b. 56 bsrl %ebx, %ecx // If the high word of b is zero, jump to 57 jz 9f // the code to handle that special case [9]. 58 59 /* High word of b is known to be non-zero on this branch */ 60 61 movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 62 63 shrl %cl, %eax // Practically, this means that bhi is given by: 64 shrl %eax // 65 notl %ecx // bhi = (high word of b) << (31 - i) | 66 shll %cl, %ebx // (low word of b) >> (1 + i) 67 orl %eax, %ebx // 68 movl 16(%esp), %edx // Load the high and low words of a, and jump 69 movl 12(%esp), %eax // to [1] if the high word is larger than bhi 70 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 71 jae 1f 72 73 /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 74 75 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 76 77 pushl %edi 78 notl %ecx 79 shrl %eax 80 shrl %cl, %eax // q = qs >> (1 + i) 81 movl %eax, %edi 82 mull 24(%esp) // q*blo 83 movl 16(%esp), %ebx 84 movl 20(%esp), %ecx // ECX:EBX = a 85 subl %eax, %ebx 86 sbbl %edx, %ecx // ECX:EBX = a - q*blo 87 movl 28(%esp), %eax 88 imull %edi, %eax // q*bhi 89 subl %eax, %ecx // ECX:EBX = a - q*b 90 sbbl $0, %edi // decrement q if remainder is negative 91 xorl %edx, %edx 92 movl %edi, %eax 93 94 addl %esi, %eax // Restore correct sign to result 95 adcl %esi, %edx 96 xorl %esi, %eax 97 xorl %esi, %edx 98 popl %edi // Restore callee-save registers 99 popl %ebx 100 popl %esi 101 retl // Return 102 103 104 1: /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 105 106 subl %ebx, %edx // subtract bhi from ahi so that divide will not 107 divl %ebx // overflow, and find q and r such that 108 // 109 // ahi:alo = (1:q)*bhi + r 110 // 111 // Note that q is a number in (31-i).(1+i) 112 // fix point. 113 114 pushl %edi 115 notl %ecx 116 shrl %eax 117 orl $0x80000000, %eax 118 shrl %cl, %eax // q = (1:qs) >> (1 + i) 119 movl %eax, %edi 120 mull 24(%esp) // q*blo 121 movl 16(%esp), %ebx 122 movl 20(%esp), %ecx // ECX:EBX = a 123 subl %eax, %ebx 124 sbbl %edx, %ecx // ECX:EBX = a - q*blo 125 movl 28(%esp), %eax 126 imull %edi, %eax // q*bhi 127 subl %eax, %ecx // ECX:EBX = a - q*b 128 sbbl $0, %edi // decrement q if remainder is negative 129 xorl %edx, %edx 130 movl %edi, %eax 131 132 addl %esi, %eax // Restore correct sign to result 133 adcl %esi, %edx 134 xorl %esi, %eax 135 xorl %esi, %edx 136 popl %edi // Restore callee-save registers 137 popl %ebx 138 popl %esi 139 retl // Return 140 141 142 9: /* High word of b is zero on this branch */ 143 144 movl 16(%esp), %eax // Find qhi and rhi such that 145 movl 20(%esp), %ecx // 146 xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b 147 divl %ecx // 148 movl %eax, %ebx // 149 movl 12(%esp), %eax // Find qlo such that 150 divl %ecx // 151 movl %ebx, %edx // rhi:alo = qlo*b + rlo with 0 rlo < b 152 153 addl %esi, %eax // Restore correct sign to result 154 adcl %esi, %edx 155 xorl %esi, %eax 156 xorl %esi, %edx 157 popl %ebx // Restore callee-save registers 158 popl %esi 159 retl // Return 160 161 #endif // __i386__ 162
