| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| |
| #include "../assembly.h" |
| |
| // du_int __umoddi3(du_int a, du_int b); |
| |
| // result = remainder of a / b. |
| // both inputs and the output are 64-bit unsigned 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(__umoddi3) |
| |
| pushl %ebx |
| movl 20(%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 16(%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 12(%esp), %edx // Load the high and low words of a, and jump |
| movl 8(%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 20(%esp) // q*blo |
| movl 12(%esp), %ebx |
| movl 16(%esp), %ecx // ECX:EBX = a |
| subl %eax, %ebx |
| sbbl %edx, %ecx // ECX:EBX = a - q*blo |
| movl 24(%esp), %eax |
| imull %edi, %eax // q*bhi |
| subl %eax, %ecx // ECX:EBX = a - q*b |
| |
| jnc 1f // if positive, this is the result. |
| addl 20(%esp), %ebx // otherwise |
| adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result |
| 1: movl %ebx, %eax |
| movl %ecx, %edx |
| |
| popl %edi |
| popl %ebx |
| retl |
| |
| |
| 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 20(%esp) // q*blo |
| movl 12(%esp), %ebx |
| movl 16(%esp), %ecx // ECX:EBX = a |
| subl %eax, %ebx |
| sbbl %edx, %ecx // ECX:EBX = a - q*blo |
| movl 24(%esp), %eax |
| imull %edi, %eax // q*bhi |
| subl %eax, %ecx // ECX:EBX = a - q*b |
| |
| jnc 3f // if positive, this is the result. |
| addl 20(%esp), %ebx // otherwise |
| adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result |
| 3: movl %ebx, %eax |
| movl %ecx, %edx |
| |
| popl %edi |
| popl %ebx |
| retl |
| |
| |
| |
| 9: /* High word of b is zero on this branch */ |
| |
| movl 12(%esp), %eax // Find qhi and rhi such that |
| movl 16(%esp), %ecx // |
| xorl %edx, %edx // ahi = qhi*b + rhi with 0 ≤ rhi < b |
| divl %ecx // |
| movl %eax, %ebx // |
| movl 8(%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 |
| retl // |
| |
| #endif // __i386__ |
