// This file is dual licensed under the MIT and the University of Illinois Open // Source Licenses. See LICENSE.TXT for details. #include "../assembly.h" // di_int __moddi3(di_int a, di_int b); // result = remainder of a / b. // both inputs and the output are 64-bit signed integers. // This will do whatever the underlying hardware is set to do on division by zero. // No other exceptions are generated, as the divide cannot overflow. // // This is targeted at 32-bit x86 *only*, as this can be done directly in hardware // on x86_64. The performance goal is ~40 cycles per divide, which is faster than // currently possible via simulation of integer divides on the x87 unit. // // Stephen Canon, December 2008 #ifdef __i386__ .text .align 4 DEFINE_COMPILERRT_FUNCTION(__moddi3) /* This is currently implemented by wrapping the unsigned modulus up in an absolute value. This could certainly be improved upon. */ pushl %esi movl 20(%esp), %edx // high word of b movl 16(%esp), %eax // low word of b movl %edx, %ecx sarl $31, %ecx // (b < 0) ? -1 : 0 xorl %ecx, %eax xorl %ecx, %edx // EDX:EAX = (b < 0) ? not(b) : b subl %ecx, %eax sbbl %ecx, %edx // EDX:EAX = abs(b) movl %edx, 20(%esp) movl %eax, 16(%esp) // store abs(b) back to stack movl 12(%esp), %edx // high word of b movl 8(%esp), %eax // low word of b movl %edx, %ecx sarl $31, %ecx // (a < 0) ? -1 : 0 xorl %ecx, %eax xorl %ecx, %edx // EDX:EAX = (a < 0) ? not(a) : a subl %ecx, %eax sbbl %ecx, %edx // EDX:EAX = abs(a) movl %edx, 12(%esp) movl %eax, 8(%esp) // store abs(a) back to stack movl %ecx, %esi // set aside sign of a pushl %ebx movl 24(%esp), %ebx // Find the index i of the leading bit in b. bsrl %ebx, %ecx // If the high word of b is zero, jump to jz 9f // the code to handle that special case [9]. /* High word of b is known to be non-zero on this branch */ movl 20(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b shrl %cl, %eax // Practically, this means that bhi is given by: shrl %eax // notl %ecx // bhi = (high word of b) << (31 - i) | shll %cl, %ebx // (low word of b) >> (1 + i) orl %eax, %ebx // movl 16(%esp), %edx // Load the high and low words of a, and jump movl 12(%esp), %eax // to [2] if the high word is larger than bhi cmpl %ebx, %edx // to avoid overflowing the upcoming divide. jae 2f /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r pushl %edi notl %ecx shrl %eax shrl %cl, %eax // q = qs >> (1 + i) movl %eax, %edi mull 24(%esp) // q*blo movl 16(%esp), %ebx movl 20(%esp), %ecx // ECX:EBX = a subl %eax, %ebx sbbl %edx, %ecx // ECX:EBX = a - q*blo movl 28(%esp), %eax imull %edi, %eax // q*bhi subl %eax, %ecx // ECX:EBX = a - q*b jnc 1f // if positive, this is the result. addl 24(%esp), %ebx // otherwise adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 1: movl %ebx, %eax movl %ecx, %edx addl %esi, %eax // Restore correct sign to result adcl %esi, %edx xorl %esi, %eax xorl %esi, %edx popl %edi // Restore callee-save registers popl %ebx popl %esi retl // Return 2: /* High word of a is greater than or equal to (b >> (1 + i)) on this branch */ subl %ebx, %edx // subtract bhi from ahi so that divide will not divl %ebx // overflow, and find q and r such that // // ahi:alo = (1:q)*bhi + r // // Note that q is a number in (31-i).(1+i) // fix point. pushl %edi notl %ecx shrl %eax orl $0x80000000, %eax shrl %cl, %eax // q = (1:qs) >> (1 + i) movl %eax, %edi mull 24(%esp) // q*blo movl 16(%esp), %ebx movl 20(%esp), %ecx // ECX:EBX = a subl %eax, %ebx sbbl %edx, %ecx // ECX:EBX = a - q*blo movl 28(%esp), %eax imull %edi, %eax // q*bhi subl %eax, %ecx // ECX:EBX = a - q*b jnc 3f // if positive, this is the result. addl 24(%esp), %ebx // otherwise adcl 28(%esp), %ecx // ECX:EBX = a - (q-1)*b = result 3: movl %ebx, %eax movl %ecx, %edx addl %esi, %eax // Restore correct sign to result adcl %esi, %edx xorl %esi, %eax xorl %esi, %edx popl %edi // Restore callee-save registers popl %ebx popl %esi retl // Return 9: /* High word of b is zero on this branch */ movl 16(%esp), %eax // Find qhi and rhi such that movl 20(%esp), %ecx // xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b divl %ecx // movl %eax, %ebx // movl 12(%esp), %eax // Find rlo such that divl %ecx // movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 ≤ rlo < b popl %ebx // xorl %edx, %edx // and return 0:rlo addl %esi, %eax // Restore correct sign to result adcl %esi, %edx xorl %esi, %eax xorl %esi, %edx popl %esi retl // Return #endif // __i386__