1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
|
/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <machine/cpu-features.h>
.text
.global memcmp
.type memcmp, %function
.align 4
/*
* Optimized memcmp() for ARM9.
* This would not be optimal on XScale or ARM11, where more prefetching
* and use of PLD will be needed.
* The 2 major optimzations here are
* (1) The main loop compares 16 bytes at a time
* (2) The loads are scheduled in a way they won't stall
*/
memcmp:
PLD (r0, #0)
PLD (r1, #0)
/* take of the case where length is 0 or the buffers are the same */
cmp r0, r1
cmpne r2, #0
moveq r0, #0
bxeq lr
/* save registers */
stmfd sp!, {r4, lr}
PLD (r0, #32)
PLD (r1, #32)
/* since r0 hold the result, move the first source
* pointer somewhere else
*/
mov r4, r0
/* make sure we have at least 8+4 bytes, this simplify things below
* and avoid some overhead for small blocks
*/
cmp r2, #(8+4)
bmi 8f
/* align first pointer to word boundary
* offset = -src & 3
*/
rsb r3, r4, #0
ands r3, r3, #3
beq 0f
/* align first pointer */
sub r2, r2, r3
1: ldrb r0, [r4], #1
ldrb ip, [r1], #1
subs r0, r0, ip
bne 9f
subs r3, r3, #1
bne 1b
0: /* here the first pointer is aligned, and we have at least 4 bytes
* to process.
*/
/* see if the pointers are congruent */
eor r0, r4, r1
ands r0, r0, #3
bne 5f
/* congruent case, 32 bytes per iteration
* We need to make sure there are at least 32+4 bytes left
* because we effectively read ahead one word, and we could
* read past the buffer (and segfault) if we're not careful.
*/
ldr ip, [r1]
subs r2, r2, #(32 + 4)
bmi 1f
0: PLD (r4, #64)
PLD (r1, #64)
ldr r0, [r4], #4
ldr lr, [r1, #4]!
eors r0, r0, ip
ldreq r0, [r4], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r4], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r4], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r4], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r4], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
ldreq r0, [r4], #4
ldreq lr, [r1, #4]!
eoreqs r0, r0, ip
ldreq r0, [r4], #4
ldreq ip, [r1, #4]!
eoreqs r0, r0, lr
bne 2f
subs r2, r2, #32
bhs 0b
/* do we have at least 4 bytes left? */
1: adds r2, r2, #(32 - 4 + 4)
bmi 4f
/* finish off 4 bytes at a time */
3: ldr r0, [r4], #4
ldr ip, [r1], #4
eors r0, r0, ip
bne 2f
subs r2, r2, #4
bhs 3b
/* are we done? */
4: adds r2, r2, #4
moveq r0, #0
beq 9f
/* finish off the remaining bytes */
b 8f
2: /* the last 4 bytes are different, restart them */
sub r4, r4, #4
sub r1, r1, #4
mov r2, #4
/* process the last few bytes */
8: ldrb r0, [r4], #1
ldrb ip, [r1], #1
// stall
subs r0, r0, ip
bne 9f
subs r2, r2, #1
bne 8b
9: /* restore registers and return */
ldmfd sp!, {r4, lr}
bx lr
5: /*************** non-congruent case ***************/
and r0, r1, #3
cmp r0, #2
bne 4f
/* here, offset is 2 (16-bits aligned, special cased) */
/* make sure we have at least 16 bytes to process */
subs r2, r2, #16
addmi r2, r2, #16
bmi 8b
/* align the unaligned pointer */
bic r1, r1, #3
ldr lr, [r1], #4
6: PLD (r1, #64)
PLD (r4, #64)
mov ip, lr, lsr #16
ldr lr, [r1], #4
ldr r0, [r4], #4
orr ip, ip, lr, lsl #16
eors r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r4], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r4], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
moveq ip, lr, lsr #16
ldreq lr, [r1], #4
ldreq r0, [r4], #4
orreq ip, ip, lr, lsl #16
eoreqs r0, r0, ip
bne 7f
subs r2, r2, #16
bhs 6b
sub r1, r1, #2
/* are we done? */
adds r2, r2, #16
moveq r0, #0
beq 9b
/* finish off the remaining bytes */
b 8b
7: /* fix up the 2 pointers and fallthrough... */
sub r1, r1, #(4+2)
sub r4, r4, #4
mov r2, #4
b 8b
4: /*************** offset is 1 or 3 (less optimized) ***************/
stmfd sp!, {r5, r6, r7}
// r5 = rhs
// r6 = lhs
// r7 = scratch
mov r5, r0, lsl #3 /* r5 = right shift */
rsb r6, r5, #32 /* r6 = left shift */
/* align the unaligned pointer */
bic r1, r1, #3
ldr r7, [r1], #4
sub r2, r2, #8
6: mov ip, r7, lsr r5
ldr r7, [r1], #4
ldr r0, [r4], #4
orr ip, ip, r7, lsl r6
eors r0, r0, ip
moveq ip, r7, lsr r5
ldreq r7, [r1], #4
ldreq r0, [r4], #4
orreq ip, ip, r7, lsl r6
eoreqs r0, r0, ip
bne 7f
subs r2, r2, #8
bhs 6b
sub r1, r1, r6, lsr #3
ldmfd sp!, {r5, r6, r7}
/* are we done? */
adds r2, r2, #8
moveq r0, #0
beq 9b
/* finish off the remaining bytes */
b 8b
7: /* fix up the 2 pointers and fallthrough... */
sub r1, r1, #4
sub r1, r1, r6, lsr #3
sub r4, r4, #4
mov r2, #4
ldmfd sp!, {r5, r6, r7}
b 8b
|
