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.balign 4
24DEFINE_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
931:	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
1052:	/* 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
1333:	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
1459:	/* 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
164END_COMPILERRT_FUNCTION(__moddi3)
165
166#endif // __i386__
167