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 __moddi3(di_int a, di_int b); 7 8 // result = remainder of 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 18 // Stephen Canon, December 2008 19 20 #ifdef __i386__ 21 22 .text 23 .align 4 24 DEFINE_COMPILERRT_FUNCTION(__moddi3) 25 26 /* This is currently implemented by wrapping the unsigned modulus up in an absolute 27 value. This could 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 41 movl 12(%esp), %edx // high word of b 42 movl 8(%esp), %eax // low word of b 43 movl %edx, %ecx 44 sarl $31, %ecx // (a < 0) ? -1 : 0 45 xorl %ecx, %eax 46 xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a 47 subl %ecx, %eax 48 sbbl %ecx, %edx // EDX:EAX = abs(a) 49 movl %edx, 12(%esp) 50 movl %eax, 8(%esp) // store abs(a) back to stack 51 movl %ecx, %esi // set aside sign of a 52 53 pushl %ebx 54 movl 24(%esp), %ebx // Find the index i of the leading bit in b. 55 bsrl %ebx, %ecx // If the high word of b is zero, jump to 56 jz 9f // the code to handle that special case [9]. 57 58 /* High word of b is known to be non-zero on this branch */ 59 60 movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b 61 62 shrl %cl, %eax // Practically, this means that bhi is given by: 63 shrl %eax // 64 notl %ecx // bhi = (high word of b) << (31 - i) | 65 shll %cl, %ebx // (low word of b) >> (1 + i) 66 orl %eax, %ebx // 67 movl 16(%esp), %edx // Load the high and low words of a, and jump 68 movl 12(%esp), %eax // to [2] if the high word is larger than bhi 69 cmpl %ebx, %edx // to avoid overflowing the upcoming divide. 70 jae 2f 71 72 /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 73 74 divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r 75 76 pushl %edi 77 notl %ecx 78 shrl %eax 79 shrl %cl, %eax // q = qs >> (1 + i) 80 movl %eax, %edi 81 mull 24(%esp) // q*blo 82 movl 16(%esp), %ebx 83 movl 20(%esp), %ecx // ECX:EBX = a 84 subl %eax, %ebx 85 sbbl %edx, %ecx // ECX:EBX = a - q*blo 86 movl 28(%esp), %eax 87 imull %edi, %eax // q*bhi 88 subl %eax, %ecx // ECX:EBX = a - q*b 89 90 jnc 1f // if positive, this is the result. 91 addl 24(%esp), %ebx // otherwise 92 adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 93 1: movl %ebx, %eax 94 movl %ecx, %edx 95 96 addl %esi, %eax // Restore correct sign to result 97 adcl %esi, %edx 98 xorl %esi, %eax 99 xorl %esi, %edx 100 popl %edi // Restore callee-save registers 101 popl %ebx 102 popl %esi 103 retl // Return 104 105 2: /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ 106 107 subl %ebx, %edx // subtract bhi from ahi so that divide will not 108 divl %ebx // overflow, and find q and r such that 109 // 110 // ahi:alo = (1:q)*bhi + r 111 // 112 // Note that q is a number in (31-i).(1+i) 113 // fix point. 114 115 pushl %edi 116 notl %ecx 117 shrl %eax 118 orl $0x80000000, %eax 119 shrl %cl, %eax // q = (1:qs) >> (1 + i) 120 movl %eax, %edi 121 mull 24(%esp) // q*blo 122 movl 16(%esp), %ebx 123 movl 20(%esp), %ecx // ECX:EBX = a 124 subl %eax, %ebx 125 sbbl %edx, %ecx // ECX:EBX = a - q*blo 126 movl 28(%esp), %eax 127 imull %edi, %eax // q*bhi 128 subl %eax, %ecx // ECX:EBX = a - q*b 129 130 jnc 3f // if positive, this is the result. 131 addl 24(%esp), %ebx // otherwise 132 adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 133 3: movl %ebx, %eax 134 movl %ecx, %edx 135 136 addl %esi, %eax // Restore correct sign to result 137 adcl %esi, %edx 138 xorl %esi, %eax 139 xorl %esi, %edx 140 popl %edi // Restore callee-save registers 141 popl %ebx 142 popl %esi 143 retl // Return 144 145 9: /* High word of b is zero on this branch */ 146 147 movl 16(%esp), %eax // Find qhi and rhi such that 148 movl 20(%esp), %ecx // 149 xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b 150 divl %ecx // 151 movl %eax, %ebx // 152 movl 12(%esp), %eax // Find rlo such that 153 divl %ecx // 154 movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 rlo < b 155 popl %ebx // 156 xorl %edx, %edx // and return 0:rlo 157 158 addl %esi, %eax // Restore correct sign to result 159 adcl %esi, %edx 160 xorl %esi, %eax 161 xorl %esi, %edx 162 popl %esi 163 retl // Return 164 165 166 #endif // __i386__ 167
