1// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
2// See https://llvm.org/LICENSE.txt for license information.
3// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
4
5#include "../assembly.h"
6
7// di_int __divdi3(di_int a, di_int b);
8
9// result = a / b.
10// both inputs and the output are 64-bit signed integers.
11// This will do whatever the underlying hardware is set to do on division by zero.
12// No other exceptions are generated, as the divide cannot overflow.
13//
14// This is targeted at 32-bit x86 *only*, as this can be done directly in hardware
15// on x86_64.  The performance goal is ~40 cycles per divide, which is faster than
16// currently possible via simulation of integer divides on the x87 unit.
17//
18// Stephen Canon, December 2008
19
20#ifdef __i386__
21
22.text
23.balign 4
24DEFINE_COMPILERRT_FUNCTION(__divdi3)
25
26// This is currently implemented by wrapping the unsigned divide up in an absolute
27// value, then restoring the correct sign at the end of the computation.  This could
28// certainly be improved upon.
29
30	pushl		%esi
31	movl	 20(%esp),			%edx	// high word of b
32	movl	 16(%esp),			%eax	// low word of b
33	movl		%edx,			%ecx
34	sarl		$31,			%ecx	// (b < 0) ? -1 : 0
35	xorl		%ecx,			%eax
36	xorl		%ecx,			%edx	// EDX:EAX = (b < 0) ? not(b) : b
37	subl		%ecx,			%eax
38	sbbl		%ecx,			%edx	// EDX:EAX = abs(b)
39	movl		%edx,		 20(%esp)
40	movl		%eax,		 16(%esp)	// store abs(b) back to stack
41	movl		%ecx,			%esi	// set aside sign of b
42
43	movl	 12(%esp),			%edx	// high word of b
44	movl	  8(%esp),			%eax	// low word of b
45	movl		%edx,			%ecx
46	sarl		$31,			%ecx	// (a < 0) ? -1 : 0
47	xorl		%ecx,			%eax
48	xorl		%ecx,			%edx	// EDX:EAX = (a < 0) ? not(a) : a
49	subl		%ecx,			%eax
50	sbbl		%ecx,			%edx	// EDX:EAX = abs(a)
51	movl		%edx,		 12(%esp)
52	movl		%eax,		  8(%esp)	// store abs(a) back to stack
53	xorl		%ecx,			%esi	// sign of result = (sign of a) ^ (sign of b)
54
55	pushl		%ebx
56	movl	 24(%esp),			%ebx	// Find the index i of the leading bit in b.
57	bsrl		%ebx,			%ecx	// If the high word of b is zero, jump to
58	jz			9f						// the code to handle that special case [9].
59
60	// High word of b is known to be non-zero on this branch
61
62	movl	 20(%esp),			%eax	// Construct bhi, containing bits [1+i:32+i] of b
63
64	shrl		%cl,			%eax	// Practically, this means that bhi is given by:
65	shrl		%eax					//
66	notl		%ecx					//		bhi = (high word of b) << (31 - i) |
67	shll		%cl,			%ebx	//			  (low word of b) >> (1 + i)
68	orl			%eax,			%ebx	//
69	movl	 16(%esp),			%edx	// Load the high and low words of a, and jump
70	movl	 12(%esp),			%eax	// to [1] if the high word is larger than bhi
71	cmpl		%ebx,			%edx	// to avoid overflowing the upcoming divide.
72	jae			1f
73
74	// High word of a is greater than or equal to (b >> (1 + i)) on this branch
75
76	divl		%ebx					// eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
77
78	pushl		%edi
79	notl		%ecx
80	shrl		%eax
81	shrl		%cl,			%eax	// q = qs >> (1 + i)
82	movl		%eax,			%edi
83	mull	 24(%esp)					// q*blo
84	movl	 16(%esp),			%ebx
85	movl	 20(%esp),			%ecx	// ECX:EBX = a
86	subl		%eax,			%ebx
87	sbbl		%edx,			%ecx	// ECX:EBX = a - q*blo
88	movl	 28(%esp),			%eax
89	imull		%edi,			%eax	// q*bhi
90	subl		%eax,			%ecx	// ECX:EBX = a - q*b
91	sbbl		$0,				%edi	// decrement q if remainder is negative
92	xorl		%edx,			%edx
93	movl		%edi,			%eax
94
95	addl		%esi,			%eax	// Restore correct sign to result
96	adcl		%esi,			%edx
97	xorl		%esi,			%eax
98	xorl		%esi,			%edx
99	popl		%edi					// Restore callee-save registers
100	popl		%ebx
101	popl		%esi
102	retl								// Return
103
104
1051:	// 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	sbbl		$0,				%edi	// decrement q if remainder is negative
130	xorl		%edx,			%edx
131	movl		%edi,			%eax
132
133	addl		%esi,			%eax	// Restore correct sign to result
134	adcl		%esi,			%edx
135	xorl		%esi,			%eax
136	xorl		%esi,			%edx
137	popl		%edi					// Restore callee-save registers
138	popl		%ebx
139	popl		%esi
140	retl								// Return
141
142
1439:	// High word of b is zero on this branch
144
145	movl	 16(%esp),			%eax	// Find qhi and rhi such that
146	movl	 20(%esp),			%ecx	//
147	xorl		%edx,			%edx	//		ahi = qhi*b + rhi	with	0 ≤ rhi < b
148	divl		%ecx					//
149	movl		%eax,			%ebx	//
150	movl	 12(%esp),			%eax	// Find qlo such that
151	divl		%ecx					//
152	movl		%ebx,			%edx	//		rhi:alo = qlo*b + rlo  with 0 ≤ rlo < b
153
154	addl		%esi,			%eax	// Restore correct sign to result
155	adcl		%esi,			%edx
156	xorl		%esi,			%eax
157	xorl		%esi,			%edx
158	popl		%ebx					// Restore callee-save registers
159	popl		%esi
160	retl								// Return
161END_COMPILERRT_FUNCTION(__divdi3)
162
163#endif // __i386__
164
165NO_EXEC_STACK_DIRECTIVE
166
167