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1da177e4 LT |
1 | /* |
2 | * linux/arch/arm/lib/div64.S | |
3 | * | |
4 | * Optimized computation of 64-bit dividend / 32-bit divisor | |
5 | * | |
6 | * Author: Nicolas Pitre | |
7 | * Created: Oct 5, 2003 | |
8 | * Copyright: Monta Vista Software, Inc. | |
9 | * | |
10 | * This program is free software; you can redistribute it and/or modify | |
11 | * it under the terms of the GNU General Public License version 2 as | |
12 | * published by the Free Software Foundation. | |
13 | */ | |
14 | ||
15 | #include <linux/linkage.h> | |
16 | ||
17 | #ifdef __ARMEB__ | |
18 | #define xh r0 | |
19 | #define xl r1 | |
20 | #define yh r2 | |
21 | #define yl r3 | |
22 | #else | |
23 | #define xl r0 | |
24 | #define xh r1 | |
25 | #define yl r2 | |
26 | #define yh r3 | |
27 | #endif | |
28 | ||
29 | /* | |
30 | * __do_div64: perform a division with 64-bit dividend and 32-bit divisor. | |
31 | * | |
32 | * Note: Calling convention is totally non standard for optimal code. | |
33 | * This is meant to be used by do_div() from include/asm/div64.h only. | |
34 | * | |
35 | * Input parameters: | |
36 | * xh-xl = dividend (clobbered) | |
37 | * r4 = divisor (preserved) | |
38 | * | |
39 | * Output values: | |
40 | * yh-yl = result | |
41 | * xh = remainder | |
42 | * | |
43 | * Clobbered regs: xl, ip | |
44 | */ | |
45 | ||
46 | ENTRY(__do_div64) | |
47 | ||
48 | @ Test for easy paths first. | |
49 | subs ip, r4, #1 | |
50 | bls 9f @ divisor is 0 or 1 | |
51 | tst ip, r4 | |
52 | beq 8f @ divisor is power of 2 | |
53 | ||
54 | @ See if we need to handle upper 32-bit result. | |
55 | cmp xh, r4 | |
56 | mov yh, #0 | |
57 | blo 3f | |
58 | ||
59 | @ Align divisor with upper part of dividend. | |
60 | @ The aligned divisor is stored in yl preserving the original. | |
61 | @ The bit position is stored in ip. | |
62 | ||
63 | #if __LINUX_ARM_ARCH__ >= 5 | |
64 | ||
65 | clz yl, r4 | |
66 | clz ip, xh | |
67 | sub yl, yl, ip | |
68 | mov ip, #1 | |
69 | mov ip, ip, lsl yl | |
70 | mov yl, r4, lsl yl | |
71 | ||
72 | #else | |
73 | ||
74 | mov yl, r4 | |
75 | mov ip, #1 | |
76 | 1: cmp yl, #0x80000000 | |
77 | cmpcc yl, xh | |
78 | movcc yl, yl, lsl #1 | |
79 | movcc ip, ip, lsl #1 | |
80 | bcc 1b | |
81 | ||
82 | #endif | |
83 | ||
84 | @ The division loop for needed upper bit positions. | |
85 | @ Break out early if dividend reaches 0. | |
86 | 2: cmp xh, yl | |
87 | orrcs yh, yh, ip | |
88 | subcss xh, xh, yl | |
89 | movnes ip, ip, lsr #1 | |
90 | mov yl, yl, lsr #1 | |
91 | bne 2b | |
92 | ||
93 | @ See if we need to handle lower 32-bit result. | |
94 | 3: cmp xh, #0 | |
95 | mov yl, #0 | |
96 | cmpeq xl, r4 | |
97 | movlo xh, xl | |
98 | movlo pc, lr | |
99 | ||
100 | @ The division loop for lower bit positions. | |
101 | @ Here we shift remainer bits leftwards rather than moving the | |
102 | @ divisor for comparisons, considering the carry-out bit as well. | |
103 | mov ip, #0x80000000 | |
104 | 4: movs xl, xl, lsl #1 | |
105 | adcs xh, xh, xh | |
106 | beq 6f | |
107 | cmpcc xh, r4 | |
108 | 5: orrcs yl, yl, ip | |
109 | subcs xh, xh, r4 | |
110 | movs ip, ip, lsr #1 | |
111 | bne 4b | |
112 | mov pc, lr | |
113 | ||
114 | @ The top part of remainder became zero. If carry is set | |
115 | @ (the 33th bit) this is a false positive so resume the loop. | |
116 | @ Otherwise, if lower part is also null then we are done. | |
117 | 6: bcs 5b | |
118 | cmp xl, #0 | |
119 | moveq pc, lr | |
120 | ||
121 | @ We still have remainer bits in the low part. Bring them up. | |
122 | ||
123 | #if __LINUX_ARM_ARCH__ >= 5 | |
124 | ||
125 | clz xh, xl @ we know xh is zero here so... | |
126 | add xh, xh, #1 | |
127 | mov xl, xl, lsl xh | |
128 | mov ip, ip, lsr xh | |
129 | ||
130 | #else | |
131 | ||
132 | 7: movs xl, xl, lsl #1 | |
133 | mov ip, ip, lsr #1 | |
134 | bcc 7b | |
135 | ||
136 | #endif | |
137 | ||
138 | @ Current remainder is now 1. It is worthless to compare with | |
139 | @ divisor at this point since divisor can not be smaller than 3 here. | |
140 | @ If possible, branch for another shift in the division loop. | |
141 | @ If no bit position left then we are done. | |
142 | movs ip, ip, lsr #1 | |
143 | mov xh, #1 | |
144 | bne 4b | |
145 | mov pc, lr | |
146 | ||
147 | 8: @ Division by a power of 2: determine what that divisor order is | |
148 | @ then simply shift values around | |
149 | ||
150 | #if __LINUX_ARM_ARCH__ >= 5 | |
151 | ||
152 | clz ip, r4 | |
153 | rsb ip, ip, #31 | |
154 | ||
155 | #else | |
156 | ||
157 | mov yl, r4 | |
158 | cmp r4, #(1 << 16) | |
159 | mov ip, #0 | |
160 | movhs yl, yl, lsr #16 | |
161 | movhs ip, #16 | |
162 | ||
163 | cmp yl, #(1 << 8) | |
164 | movhs yl, yl, lsr #8 | |
165 | addhs ip, ip, #8 | |
166 | ||
167 | cmp yl, #(1 << 4) | |
168 | movhs yl, yl, lsr #4 | |
169 | addhs ip, ip, #4 | |
170 | ||
171 | cmp yl, #(1 << 2) | |
172 | addhi ip, ip, #3 | |
173 | addls ip, ip, yl, lsr #1 | |
174 | ||
175 | #endif | |
176 | ||
177 | mov yh, xh, lsr ip | |
178 | mov yl, xl, lsr ip | |
179 | rsb ip, ip, #32 | |
180 | orr yl, yl, xh, lsl ip | |
181 | mov xh, xl, lsl ip | |
182 | mov xh, xh, lsr ip | |
183 | mov pc, lr | |
184 | ||
185 | @ eq -> division by 1: obvious enough... | |
186 | 9: moveq yl, xl | |
187 | moveq yh, xh | |
188 | moveq xh, #0 | |
189 | moveq pc, lr | |
190 | ||
191 | @ Division by 0: | |
192 | str lr, [sp, #-4]! | |
193 | bl __div0 | |
194 | ||
195 | @ as wrong as it could be... | |
196 | mov yl, #0 | |
197 | mov yh, #0 | |
198 | mov xh, #0 | |
199 | ldr pc, [sp], #4 | |
200 |