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
|
/* memchr implemented using NEON.
Copyright (C) 2011-2024 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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* For __ARM_NEON__ this file defines memchr. */
#ifndef __ARM_NEON__
# define memchr __memchr_neon
# undef libc_hidden_builtin_def
# define libc_hidden_builtin_def(a)
#endif
.arch armv7-a
.fpu neon
/* Arguments */
#define srcin r0
#define chrin r1
#define cntin r2
/* Retval */
#define result r0 /* Live range does not overlap with srcin */
/* Working registers */
#define src r1 /* Live range does not overlap with chrin */
#define tmp r3
#define synd r0 /* No overlap with srcin or result */
#define soff r12
/* Working NEON registers */
#define vrepchr q0
#define vdata0 q1
#define vdata0_0 d2 /* Lower half of vdata0 */
#define vdata0_1 d3 /* Upper half of vdata0 */
#define vdata1 q2
#define vdata1_0 d4 /* Lower half of vhas_chr0 */
#define vdata1_1 d5 /* Upper half of vhas_chr0 */
#define vrepmask q3
#define vrepmask0 d6
#define vrepmask1 d7
#define vend q4
#define vend0 d8
#define vend1 d9
/*
* Core algorithm:
*
* For each 32-byte chunk we calculate a 32-bit syndrome value, with one bit per
* byte. Each bit is set if the relevant byte matched the requested character
* and cleared otherwise. Since the bits in the syndrome reflect exactly the
* order in which things occur in the original string, counting trailing zeros
* allows to identify exactly which byte has matched.
*/
.thumb_func
.p2align 4,,15
ENTRY(memchr)
/* Use a simple loop if there are less than 8 bytes to search. */
cmp cntin, #7
bhi .Llargestr
and chrin, chrin, #0xff
.Lsmallstr:
subs cntin, cntin, #1
blo .Lnotfound /* Return not found if reached end. */
ldrb tmp, [srcin], #1
cmp tmp, chrin
bne .Lsmallstr /* Loop again if not found. */
/* Otherwise fixup address and return. */
sub result, srcin, #1
bx lr
.Llargestr:
vdup.8 vrepchr, chrin /* Duplicate char across all lanes. */
/*
* Magic constant 0x8040201008040201 allows us to identify which lane
* matches the requested byte.
*/
movw tmp, #0x0201
movt tmp, #0x0804
lsl soff, tmp, #4
vmov vrepmask0, tmp, soff
vmov vrepmask1, tmp, soff
/* Work with aligned 32-byte chunks */
bic src, srcin, #31
ands soff, srcin, #31
beq .Lloopintro /* Go straight to main loop if it's aligned. */
/*
* Input string is not 32-byte aligned. We calculate the syndrome
* value for the aligned 32 bytes block containing the first bytes
* and mask the irrelevant part.
*/
vld1.8 {vdata0, vdata1}, [src:256]!
sub tmp, soff, #32
adds cntin, cntin, tmp
vceq.i8 vdata0, vdata0, vrepchr
vceq.i8 vdata1, vdata1, vrepchr
vand vdata0, vdata0, vrepmask
vand vdata1, vdata1, vrepmask
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
vmov synd, vdata0_0[0]
/* Clear the soff lower bits */
lsr synd, synd, soff
lsl synd, synd, soff
/* The first block can also be the last */
bls .Lmasklast
/* Have we found something already? */
cbnz synd, .Ltail
.Lloopintro:
vpush {vend}
/* 264/265 correspond to d8/d9 for q4 */
cfi_adjust_cfa_offset (16)
cfi_rel_offset (264, 0)
cfi_rel_offset (265, 8)
.p2align 3,,7
.Lloop:
vld1.8 {vdata0, vdata1}, [src:256]!
subs cntin, cntin, #32
vceq.i8 vdata0, vdata0, vrepchr
vceq.i8 vdata1, vdata1, vrepchr
/* If we're out of data we finish regardless of the result. */
bls .Lend
/* Use a fast check for the termination condition. */
vorr vend, vdata0, vdata1
vorr vend0, vend0, vend1
vmov synd, tmp, vend0
orrs synd, synd, tmp
/* We're not out of data, loop if we haven't found the character. */
beq .Lloop
.Lend:
vpop {vend}
cfi_adjust_cfa_offset (-16)
cfi_restore (264)
cfi_restore (265)
/* Termination condition found, let's calculate the syndrome value. */
vand vdata0, vdata0, vrepmask
vand vdata1, vdata1, vrepmask
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
vmov synd, vdata0_0[0]
cbz synd, .Lnotfound
bhi .Ltail /* Uses the condition code from
subs cntin, cntin, #32 above. */
.Lmasklast:
/* Clear the (-cntin) upper bits to avoid out-of-bounds matches. */
neg cntin, cntin
lsl synd, synd, cntin
lsrs synd, synd, cntin
it eq
moveq src, #0 /* If no match, set src to 0 so the retval is 0. */
.Ltail:
/* Count the trailing zeros using bit reversing */
rbit synd, synd
/* Compensate the last post-increment */
sub src, src, #32
/* Count the leading zeros */
clz synd, synd
/* Compute the potential result and return */
add result, src, synd
bx lr
.Lnotfound:
/* Set result to NULL if not found and return */
mov result, #0
bx lr
END(memchr)
libc_hidden_builtin_def (memchr)
|
