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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> | |
6ebbf2ce | 16 | #include <asm/assembler.h> |
01885bc5 | 17 | #include <asm/unwind.h> |
4dd1837d | 18 | #include <asm/export.h> |
1da177e4 LT |
19 | |
20 | #ifdef __ARMEB__ | |
21 | #define xh r0 | |
22 | #define xl r1 | |
23 | #define yh r2 | |
24 | #define yl r3 | |
25 | #else | |
26 | #define xl r0 | |
27 | #define xh r1 | |
28 | #define yl r2 | |
29 | #define yh r3 | |
30 | #endif | |
31 | ||
32 | /* | |
33 | * __do_div64: perform a division with 64-bit dividend and 32-bit divisor. | |
34 | * | |
35 | * Note: Calling convention is totally non standard for optimal code. | |
36 | * This is meant to be used by do_div() from include/asm/div64.h only. | |
37 | * | |
38 | * Input parameters: | |
39 | * xh-xl = dividend (clobbered) | |
40 | * r4 = divisor (preserved) | |
41 | * | |
42 | * Output values: | |
43 | * yh-yl = result | |
44 | * xh = remainder | |
45 | * | |
46 | * Clobbered regs: xl, ip | |
47 | */ | |
48 | ||
49 | ENTRY(__do_div64) | |
01885bc5 | 50 | UNWIND(.fnstart) |
1da177e4 LT |
51 | |
52 | @ Test for easy paths first. | |
53 | subs ip, r4, #1 | |
54 | bls 9f @ divisor is 0 or 1 | |
55 | tst ip, r4 | |
56 | beq 8f @ divisor is power of 2 | |
57 | ||
58 | @ See if we need to handle upper 32-bit result. | |
59 | cmp xh, r4 | |
60 | mov yh, #0 | |
61 | blo 3f | |
62 | ||
63 | @ Align divisor with upper part of dividend. | |
64 | @ The aligned divisor is stored in yl preserving the original. | |
65 | @ The bit position is stored in ip. | |
66 | ||
67 | #if __LINUX_ARM_ARCH__ >= 5 | |
68 | ||
69 | clz yl, r4 | |
70 | clz ip, xh | |
71 | sub yl, yl, ip | |
72 | mov ip, #1 | |
73 | mov ip, ip, lsl yl | |
74 | mov yl, r4, lsl yl | |
75 | ||
76 | #else | |
77 | ||
78 | mov yl, r4 | |
79 | mov ip, #1 | |
80 | 1: cmp yl, #0x80000000 | |
81 | cmpcc yl, xh | |
82 | movcc yl, yl, lsl #1 | |
83 | movcc ip, ip, lsl #1 | |
84 | bcc 1b | |
85 | ||
86 | #endif | |
87 | ||
88 | @ The division loop for needed upper bit positions. | |
89 | @ Break out early if dividend reaches 0. | |
90 | 2: cmp xh, yl | |
91 | orrcs yh, yh, ip | |
92 | subcss xh, xh, yl | |
93 | movnes ip, ip, lsr #1 | |
94 | mov yl, yl, lsr #1 | |
95 | bne 2b | |
96 | ||
97 | @ See if we need to handle lower 32-bit result. | |
98 | 3: cmp xh, #0 | |
99 | mov yl, #0 | |
100 | cmpeq xl, r4 | |
101 | movlo xh, xl | |
6ebbf2ce | 102 | retlo lr |
1da177e4 LT |
103 | |
104 | @ The division loop for lower bit positions. | |
105 | @ Here we shift remainer bits leftwards rather than moving the | |
106 | @ divisor for comparisons, considering the carry-out bit as well. | |
107 | mov ip, #0x80000000 | |
108 | 4: movs xl, xl, lsl #1 | |
109 | adcs xh, xh, xh | |
110 | beq 6f | |
111 | cmpcc xh, r4 | |
112 | 5: orrcs yl, yl, ip | |
113 | subcs xh, xh, r4 | |
114 | movs ip, ip, lsr #1 | |
115 | bne 4b | |
6ebbf2ce | 116 | ret lr |
1da177e4 LT |
117 | |
118 | @ The top part of remainder became zero. If carry is set | |
119 | @ (the 33th bit) this is a false positive so resume the loop. | |
120 | @ Otherwise, if lower part is also null then we are done. | |
121 | 6: bcs 5b | |
122 | cmp xl, #0 | |
6ebbf2ce | 123 | reteq lr |
1da177e4 LT |
124 | |
125 | @ We still have remainer bits in the low part. Bring them up. | |
126 | ||
127 | #if __LINUX_ARM_ARCH__ >= 5 | |
128 | ||
129 | clz xh, xl @ we know xh is zero here so... | |
130 | add xh, xh, #1 | |
131 | mov xl, xl, lsl xh | |
132 | mov ip, ip, lsr xh | |
133 | ||
134 | #else | |
135 | ||
136 | 7: movs xl, xl, lsl #1 | |
137 | mov ip, ip, lsr #1 | |
138 | bcc 7b | |
139 | ||
140 | #endif | |
141 | ||
142 | @ Current remainder is now 1. It is worthless to compare with | |
143 | @ divisor at this point since divisor can not be smaller than 3 here. | |
144 | @ If possible, branch for another shift in the division loop. | |
145 | @ If no bit position left then we are done. | |
146 | movs ip, ip, lsr #1 | |
147 | mov xh, #1 | |
148 | bne 4b | |
6ebbf2ce | 149 | ret lr |
1da177e4 LT |
150 | |
151 | 8: @ Division by a power of 2: determine what that divisor order is | |
152 | @ then simply shift values around | |
153 | ||
154 | #if __LINUX_ARM_ARCH__ >= 5 | |
155 | ||
156 | clz ip, r4 | |
157 | rsb ip, ip, #31 | |
158 | ||
159 | #else | |
160 | ||
161 | mov yl, r4 | |
162 | cmp r4, #(1 << 16) | |
163 | mov ip, #0 | |
164 | movhs yl, yl, lsr #16 | |
165 | movhs ip, #16 | |
166 | ||
167 | cmp yl, #(1 << 8) | |
168 | movhs yl, yl, lsr #8 | |
169 | addhs ip, ip, #8 | |
170 | ||
171 | cmp yl, #(1 << 4) | |
172 | movhs yl, yl, lsr #4 | |
173 | addhs ip, ip, #4 | |
174 | ||
175 | cmp yl, #(1 << 2) | |
176 | addhi ip, ip, #3 | |
177 | addls ip, ip, yl, lsr #1 | |
178 | ||
179 | #endif | |
180 | ||
181 | mov yh, xh, lsr ip | |
182 | mov yl, xl, lsr ip | |
183 | rsb ip, ip, #32 | |
8b592783 CM |
184 | ARM( orr yl, yl, xh, lsl ip ) |
185 | THUMB( lsl xh, xh, ip ) | |
186 | THUMB( orr yl, yl, xh ) | |
1da177e4 LT |
187 | mov xh, xl, lsl ip |
188 | mov xh, xh, lsr ip | |
6ebbf2ce | 189 | ret lr |
1da177e4 LT |
190 | |
191 | @ eq -> division by 1: obvious enough... | |
192 | 9: moveq yl, xl | |
193 | moveq yh, xh | |
194 | moveq xh, #0 | |
6ebbf2ce | 195 | reteq lr |
01885bc5 | 196 | UNWIND(.fnend) |
1da177e4 | 197 | |
01885bc5 LA |
198 | UNWIND(.fnstart) |
199 | UNWIND(.pad #4) | |
200 | UNWIND(.save {lr}) | |
201 | Ldiv0_64: | |
1da177e4 | 202 | @ Division by 0: |
1d6760a3 | 203 | str lr, [sp, #-8]! |
1da177e4 LT |
204 | bl __div0 |
205 | ||
206 | @ as wrong as it could be... | |
207 | mov yl, #0 | |
208 | mov yh, #0 | |
209 | mov xh, #0 | |
1d6760a3 | 210 | ldr pc, [sp], #8 |
1da177e4 | 211 | |
01885bc5 | 212 | UNWIND(.fnend) |
93ed3970 | 213 | ENDPROC(__do_div64) |
4dd1837d | 214 | EXPORT_SYMBOL(__do_div64) |