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
|
/* strnlen - calculate the length of a string with limit.
Copyright (C) 2013-2023 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>
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD.
* MTE compatible.
*/
#define srcin x0
#define cntin x1
#define result x0
#define src x2
#define synd x3
#define shift x4
#define tmp x4
#define cntrem x5
#define qdata q0
#define vdata v0
#define vhas_chr v1
#define vend v2
#define dend d2
/*
Core algorithm:
For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits
per byte. We take 4 bits of every comparison byte with shift right and narrow
by 4 instruction. Since the bits in the nibble mask reflect the order in
which things occur in the original string, counting trailing zeros identifies
exactly which byte matched. */
ENTRY (__strnlen)
PTR_ARG (0)
SIZE_ARG (1)
bic src, srcin, 15
cbz cntin, L(nomatch)
ld1 {vdata.16b}, [src], 16
cmeq vhas_chr.16b, vdata.16b, 0
lsl shift, srcin, 2
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
fmov synd, dend
lsr synd, synd, shift
cbz synd, L(start_loop)
L(finish):
rbit synd, synd
clz synd, synd
lsr result, synd, 2
cmp cntin, result
csel result, cntin, result, ls
ret
L(start_loop):
sub tmp, src, srcin
subs cntrem, cntin, tmp
b.ls L(nomatch)
/* Make sure that it won't overread by a 16-byte chunk */
add tmp, cntrem, 15
tbnz tmp, 4, L(loop32_2)
.p2align 5
L(loop32):
ldr qdata, [src], 16
cmeq vhas_chr.16b, vdata.16b, 0
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbnz synd, L(end)
L(loop32_2):
ldr qdata, [src], 16
subs cntrem, cntrem, 32
cmeq vhas_chr.16b, vdata.16b, 0
b.ls L(end)
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbz synd, L(loop32)
L(end):
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
sub src, src, 16
mov synd, vend.d[0]
sub result, src, srcin
#ifndef __AARCH64EB__
rbit synd, synd
#endif
clz synd, synd
add result, result, synd, lsr 2
cmp cntin, result
csel result, cntin, result, ls
ret
L(nomatch):
mov result, cntin
ret
END (__strnlen)
libc_hidden_def (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_def (strnlen)
|
