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
|
/* strchr -- find the first instance of C in a nul-terminated string.
Copyright (C) 2013-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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>
.syntax unified
.text
ENTRY (strchr)
@ r0 = start of string
@ r1 = character to match
@ returns NULL for no match, or a pointer to the match
sfi_breg r0, \
ldrb r2, [\B] @ load the first byte asap
uxtb r1, r1
@ To cater to long strings, we want to search through a few
@ characters until we reach an aligned pointer. To cater to
@ small strings, we don't want to start doing word operations
@ immediately. The compromise is a maximum of 16 bytes less
@ whatever is required to end with an aligned pointer.
@ r3 = number of characters to search in alignment loop
and r3, r0, #7
rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
cmp r2, r1 @ Found C?
it ne
cmpne r2, #0 @ Found EOS?
beq 99f
@ Loop until we find ...
1: sfi_breg r0, \
ldrb r2, [\B, #1]!
subs r3, r3, #1 @ ... the aligment point
it ne
cmpne r2, r1 @ ... or the character
it ne
cmpne r2, #0 @ ... or EOS
bne 1b
@ Disambiguate the exit possibilites above
cmp r2, r1 @ Found the character
it ne
cmpne r2, #0 @ Found EOS
beq 99f
add r0, r0, #1
@ So now we're aligned. Now we actually need a stack frame.
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)
sfi_breg r0, \
ldrd r2, r3, [\B], #8
orr r1, r1, r1, lsl #8 @ Replicate C to all bytes
#ifdef ARCH_HAS_T2
movw ip, #0x0101
sfi_pld r0, #64
movt ip, #0x0101
#else
ldr ip, =0x01010101
sfi_pld r0, #64
#endif
orr r1, r1, r1, lsl #16
@ Loop searching for EOS or C, 8 bytes at a time.
2:
@ Subtracting (unsigned saturating) from 1 means result of 1 for
@ any byte that was originally zero and 0 otherwise. Therefore
@ we consider the lsb of each byte the "found" bit.
uqsub8 r4, ip, r2 @ Find EOS
eor r6, r2, r1 @ Convert C bytes to 0
uqsub8 r5, ip, r3
eor r7, r3, r1
uqsub8 r6, ip, r6 @ Find C
sfi_pld r0, #128 @ Prefetch 2 lines ahead
uqsub8 r7, ip, r7
orr r4, r4, r6 @ Combine found for EOS and C
orr r5, r5, r7
orrs r6, r4, r5 @ Combine the two words
it eq
sfi_breg r0, \
ldrdeq r2, r3, [\B], #8
beq 2b
@ Found something. Disambiguate between first and second words.
@ Adjust r0 to point to the word containing the match.
@ Adjust r2 to the contents of the word containing the match.
@ Adjust r4 to the found bits for the word containing the match.
cmp r4, #0
sub r0, r0, #4
itte eq
moveq r4, r5
moveq r2, r3
subne r0, r0, #4
@ Find the bit-offset of the match within the word.
#if defined(__ARMEL__)
@ For LE, swap the found word so clz searches from the little end.
rev r4, r4
#else
@ For BE, byte swap the word to make it easier to extract the byte.
rev r2, r2
#endif
@ We're counting 0x01 (not 0x80), so the bit offset is 7 too high.
clz r3, r4
sub r3, r3, #7
lsr r2, r2, r3 @ Shift down found byte
uxtb r1, r1 @ Undo replication of C
uxtb r2, r2 @ Extract found byte
add r0, r0, r3, lsr #3 @ Adjust the pointer to the found byte
pop { r4, r5, r6, r7 }
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
@ Disambiguate between EOS and C.
99:
cmp r2, r1
it ne
movne r0, #0 @ Found EOS, return NULL
bx lr
END (strchr)
weak_alias (strchr, index)
libc_hidden_builtin_def (strchr)
|
