1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * Copyright (C) 2013 ARM Ltd.
4 * Copyright (C) 2013 Linaro.
5 *
6 * This code is based on glibc cortex strings
7 * be found @
8 *
9 * http://bazaar.launchpad.net/~linaro-toolcha
10 * files/head:/src/aarch64/
11 */
12
13 #include <linux/linkage.h>
14 #include <asm/assembler.h>
15
16 /*
17 * determine the length of a fixed-size string
18 *
19 * Parameters:
20 * x0 - const string pointer
21 * x1 - maximal string length
22 * Returns:
23 * x0 - the return length of specific str
24 */
25
26 /* Arguments and results. */
27 srcin .req x0
28 len .req x0
29 limit .req x1
30
31 /* Locals and temporaries. */
32 src .req x2
33 data1 .req x3
34 data2 .req x4
35 data2a .req x5
36 has_nul1 .req x6
37 has_nul2 .req x7
38 tmp1 .req x8
39 tmp2 .req x9
40 tmp3 .req x10
41 tmp4 .req x11
42 zeroones .req x12
43 pos .req x13
44 limit_wd .req x14
45
46 #define REP8_01 0x0101010101010101
47 #define REP8_7f 0x7f7f7f7f7f7f7f7f
48 #define REP8_80 0x8080808080808080
49
50 SYM_FUNC_START(__pi_strnlen)
51 cbz limit, .Lhit_limit
52 mov zeroones, #REP8_01
53 bic src, srcin, #15
54 ands tmp1, srcin, #15
55 b.ne .Lmisaligned
56 /* Calculate the number of full and pa
57 sub limit_wd, limit, #1 /* Limit !
58 lsr limit_wd, limit_wd, #4 /* Con
59
60 /*
61 * NUL detection works on the principle
62 * (=> (X - 1) & ~(X | 0x7f)) is non-ze
63 * can be done in parallel across the e
64 */
65 /*
66 * The inner loop deals with two Dwords
67 * slightly higher start-up cost, but w
68 * especially on cores with a high numb
69 * cycle, as we get much better paralle
70 */
71 .Lloop:
72 ldp data1, data2, [src], #16
73 .Lrealigned:
74 sub tmp1, data1, zeroones
75 orr tmp2, data1, #REP8_7f
76 sub tmp3, data2, zeroones
77 orr tmp4, data2, #REP8_7f
78 bic has_nul1, tmp1, tmp2
79 bic has_nul2, tmp3, tmp4
80 subs limit_wd, limit_wd, #1
81 orr tmp1, has_nul1, has_nul2
82 ccmp tmp1, #0, #0, pl /* NZCV =
83 b.eq .Lloop
84
85 cbz tmp1, .Lhit_limit /* No null
86
87 /*
88 * We know there's a null in the final
89 * to do now is work out the length of
90 * MIN (len, limit).
91 */
92 sub len, src, srcin
93 cbz has_nul1, .Lnul_in_data2
94 CPU_BE( mov data2, data1 ) /*perpare data
95
96 sub len, len, #8
97 mov has_nul2, has_nul1
98 .Lnul_in_data2:
99 /*
100 * For big-endian, carry propagation (i
101 * string is 0x01) means we cannot use
102 * easiest way to get the correct byte
103 * and calculate the syndrome a second
104 */
105 CPU_BE( rev data2, data2 )
106 CPU_BE( sub tmp1, data2, zeroones )
107 CPU_BE( orr tmp2, data2, #REP8_7f )
108 CPU_BE( bic has_nul2, tmp1, tmp2 )
109
110 sub len, len, #8
111 rev has_nul2, has_nul2
112 clz pos, has_nul2
113 add len, len, pos, lsr #3 /*
114 cmp len, limit
115 csel len, len, limit, ls /* Ret
116 ret
117
118 .Lmisaligned:
119 /*
120 * Deal with a partial first word.
121 * We're doing two things in parallel h
122 * 1) Calculate the number of words (bu
123 * limit is near ULONG_MAX) - to do thi
124 * limit + tmp1 - 1 as a 65-bit value b
125 * 2) Load and mask the initial data wo
126 * before the ones we are interested in
127 * early bytes will not hit any zero de
128 */
129 ldp data1, data2, [src], #16
130
131 sub limit_wd, limit, #1
132 and tmp3, limit_wd, #15
133 lsr limit_wd, limit_wd, #4
134
135 add tmp3, tmp3, tmp1
136 add limit_wd, limit_wd, tmp3, lsr
137
138 neg tmp4, tmp1
139 lsl tmp4, tmp4, #3 /* Bytes beyon
140
141 mov tmp2, #~0
142 /* Big-endian. Early bytes are at MSB
143 CPU_BE( lsl tmp2, tmp2, tmp4 ) /* Shi
144 /* Little-endian. Early bytes are at
145 CPU_LE( lsr tmp2, tmp2, tmp4 ) /* Shi
146
147 cmp tmp1, #8
148
149 orr data1, data1, tmp2
150 orr data2a, data2, tmp2
151
152 csinv data1, data1, xzr, le
153 csel data2, data2, data2a, le
154 b .Lrealigned
155
156 .Lhit_limit:
157 mov len, limit
158 ret
159 SYM_FUNC_END(__pi_strnlen)
160
161 SYM_FUNC_ALIAS_WEAK(strnlen, __pi_strnlen)
162 EXPORT_SYMBOL_NOKASAN(strnlen)
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