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
|
/* Copyright (C) 2011-2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Code contributed by Dave Gilbert <david.gilbert@linaro.org>
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
@ and ARMv6T2 processors. It has a fast path for short sizes, and has an
@ optimised path for large data sets; the worst case is finding the match early
@ in a large data set.
@ Note: The use of cbz/cbnz means it's Thumb only
@ 2011-07-15 david.gilbert@linaro.org
@ Copy from Cortex strings release 21 and change license
@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
@ Change function declarations/entry/exit
@ 2011-12-01 david.gilbert@linaro.org
@ Add some fixes from comments received (including use of ldrd instead ldm)
@ 2011-12-07 david.gilbert@linaro.org
@ Removed cbz from align loop - can't be taken
@ this lets us check a flag in a 00/ff byte easily in either endianness
#ifdef __ARMEB__
#define CHARTSTMASK(c) 1<<(31-(c*8))
#else
#define CHARTSTMASK(c) 1<<(c*8)
#endif
.syntax unified
.text
#ifdef NO_THUMB
.arm
#else
.thumb
.thumb_func
#endif
.global memchr
.type memchr,%function
ENTRY(memchr)
@ r0 = start of memory to scan
@ r1 = character to look for
@ r2 = length
@ returns r0 = pointer to character or NULL if not found
and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char
cmp r2,#16 @ If it's short don't bother with anything clever
blt 20f
tst r0, #7 @ If it's already aligned skip the next bit
beq 10f
@ Work up to an aligned point
5:
ldrb r3, [r0],#1
subs r2, r2, #1
cmp r3, r1
beq 50f @ If it matches exit found
tst r0, #7
bne 5b @ If not aligned yet then do next byte
10:
@ At this point, we are aligned, we know we have at least 8 bytes to work with
push {r4,r5,r6,r7}
cfi_adjust_cfa_offset (16)
cfi_rel_offset (r4, 0)
cfi_rel_offset (r5, 4)
cfi_rel_offset (r6, 8)
cfi_rel_offset (r7, 12)
cfi_remember_state
orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
orr r1, r1, r1, lsl #16
bic r6, r2, #7 @ Number of double words to work with * 8
mvns r7, #0 @ all F's
movs r3, #0
15:
ldrd r4,r5, [r0],#8
#ifndef NO_THUMB
subs r6, r6, #8
#endif
eor r4,r4, r1 @ Get it so that r4,r5 have 00's where the bytes match the target
eor r5,r5, r1
uadd8 r4, r4, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r4, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r5, r4, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
#ifndef NO_THUMB
cbnz r5, 60f
#else
cmp r5, #0
bne 60f
subs r6, r6, #8
#endif
bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
pop {r4,r5,r6,r7}
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done
20:
#ifndef NO_THUMB
cbz r2, 40f @ 0 length or hit the end already then not found
#else
cmp r2, #0
beq 40f
#endif
21: @ Post aligned section, or just a short call
ldrb r3,[r0],#1
#ifndef NO_THUMB
subs r2,r2,#1
eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
cbz r3, 50f
#else
eors r3, r3, r1
beq 50f
subs r2, r2, #1
#endif
bne 21b @ on r2 flags
40:
movs r0,#0 @ not found
DO_RET(lr)
50:
subs r0,r0,#1 @ found
DO_RET(lr)
60: @ We're here because the fast path found a hit - now we have to track down exactly which word it was
@ r0 points to the start of the double word after the one that was tested
@ r4 has the 00/ff pattern for the first word, r5 has the chained value
cfi_restore_state
cmp r4, #0
itte eq
moveq r4, r5 @ the end is in the 2nd word
subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
subne r0,r0,#7 @ or 2nd byte of 1st word
@ r0 currently points to the 2nd byte of the word containing the hit
tst r4, # CHARTSTMASK(0) @ 1st character
bne 61f
adds r0,r0,#1
tst r4, # CHARTSTMASK(1) @ 2nd character
ittt eq
addeq r0,r0,#1
tsteq r4, # (3<<15) @ 2nd & 3rd character
@ If not the 3rd must be the last one
addeq r0,r0,#1
61:
pop {r4,r5,r6,r7}
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
subs r0,r0,#1
DO_RET(lr)
END(memchr)
libc_hidden_builtin_def (memchr)
|
