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1 | /* strnlen - calculate the length of a string with limit. |
2 | ||
b168057a | 3 | Copyright (C) 2013-2015 Free Software Foundation, Inc. |
4499bb3e MS |
4 | |
5 | This file is part of the GNU C Library. | |
6 | ||
7 | The GNU C Library is free software; you can redistribute it and/or | |
8 | modify it under the terms of the GNU Lesser General Public | |
9 | License as published by the Free Software Foundation; either | |
10 | version 2.1 of the License, or (at your option) any later version. | |
11 | ||
12 | The GNU C Library is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Lesser General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public | |
18 | License along with the GNU C Library. If not, see | |
19 | <http://www.gnu.org/licenses/>. */ | |
20 | ||
21 | #include <sysdep.h> | |
22 | ||
23 | /* Assumptions: | |
24 | * | |
25 | * ARMv8-a, AArch64 | |
26 | */ | |
27 | ||
28 | /* Arguments and results. */ | |
29 | #define srcin x0 | |
30 | #define len x0 | |
31 | #define limit x1 | |
32 | ||
33 | /* Locals and temporaries. */ | |
34 | #define src x2 | |
35 | #define data1 x3 | |
36 | #define data2 x4 | |
37 | #define data2a x5 | |
38 | #define has_nul1 x6 | |
39 | #define has_nul2 x7 | |
40 | #define tmp1 x8 | |
41 | #define tmp2 x9 | |
42 | #define tmp3 x10 | |
43 | #define tmp4 x11 | |
44 | #define zeroones x12 | |
45 | #define pos x13 | |
46 | #define limit_wd x14 | |
47 | ||
48 | #define REP8_01 0x0101010101010101 | |
49 | #define REP8_7f 0x7f7f7f7f7f7f7f7f | |
50 | #define REP8_80 0x8080808080808080 | |
51 | ||
52 | ENTRY_ALIGN_AND_PAD (__strnlen, 6, 9) | |
53 | cbz limit, L(hit_limit) | |
54 | mov zeroones, #REP8_01 | |
55 | bic src, srcin, #15 | |
56 | ands tmp1, srcin, #15 | |
57 | b.ne L(misaligned) | |
58 | /* Calculate the number of full and partial words -1. */ | |
59 | sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */ | |
60 | lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */ | |
61 | ||
62 | /* NUL detection works on the principle that (X - 1) & (~X) & 0x80 | |
63 | (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and | |
64 | can be done in parallel across the entire word. */ | |
65 | /* The inner loop deals with two Dwords at a time. This has a | |
66 | slightly higher start-up cost, but we should win quite quickly, | |
67 | especially on cores with a high number of issue slots per | |
68 | cycle, as we get much better parallelism out of the operations. */ | |
69 | ||
70 | /* Start of critial section -- keep to one 64Byte cache line. */ | |
71 | L(loop): | |
72 | ldp data1, data2, [src], #16 | |
73 | L(realigned): | |
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 = 0000 */ | |
83 | b.eq L(loop) | |
84 | /* End of critical section -- keep to one 64Byte cache line. */ | |
85 | ||
86 | orr tmp1, has_nul1, has_nul2 | |
87 | cbz tmp1, L(hit_limit) /* No null in final Qword. */ | |
88 | ||
89 | /* We know there's a null in the final Qword. The easiest thing | |
90 | to do now is work out the length of the string and return | |
91 | MIN (len, limit). */ | |
92 | ||
93 | sub len, src, srcin | |
94 | cbz has_nul1, L(nul_in_data2) | |
95 | #ifdef __AARCH64EB__ | |
96 | mov data2, data1 | |
97 | #endif | |
98 | sub len, len, #8 | |
99 | mov has_nul2, has_nul1 | |
100 | L(nul_in_data2): | |
101 | #ifdef __AARCH64EB__ | |
102 | /* For big-endian, carry propagation (if the final byte in the | |
103 | string is 0x01) means we cannot use has_nul directly. The | |
104 | easiest way to get the correct byte is to byte-swap the data | |
105 | and calculate the syndrome a second time. */ | |
106 | rev data2, data2 | |
107 | sub tmp1, data2, zeroones | |
108 | orr tmp2, data2, #REP8_7f | |
109 | bic has_nul2, tmp1, tmp2 | |
110 | #endif | |
111 | sub len, len, #8 | |
112 | rev has_nul2, has_nul2 | |
113 | clz pos, has_nul2 | |
114 | add len, len, pos, lsr #3 /* Bits to bytes. */ | |
115 | cmp len, limit | |
116 | csel len, len, limit, ls /* Return the lower value. */ | |
117 | RET | |
118 | ||
119 | L(misaligned): | |
120 | /* Deal with a partial first word. | |
121 | We're doing two things in parallel here; | |
122 | 1) Calculate the number of words (but avoiding overflow if | |
123 | limit is near ULONG_MAX) - to do this we need to work out | |
124 | limit + tmp1 - 1 as a 65-bit value before shifting it; | |
125 | 2) Load and mask the initial data words - we force the bytes | |
126 | before the ones we are interested in to 0xff - this ensures | |
127 | early bytes will not hit any zero detection. */ | |
128 | sub limit_wd, limit, #1 | |
129 | neg tmp4, tmp1 | |
130 | cmp tmp1, #8 | |
131 | ||
132 | and tmp3, limit_wd, #15 | |
133 | lsr limit_wd, limit_wd, #4 | |
134 | mov tmp2, #~0 | |
135 | ||
136 | ldp data1, data2, [src], #16 | |
137 | lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */ | |
138 | add tmp3, tmp3, tmp1 | |
139 | ||
140 | #ifdef __AARCH64EB__ | |
141 | /* Big-endian. Early bytes are at MSB. */ | |
142 | lsl tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */ | |
143 | #else | |
144 | /* Little-endian. Early bytes are at LSB. */ | |
145 | lsr tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */ | |
146 | #endif | |
147 | add limit_wd, limit_wd, tmp3, lsr #4 | |
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 L(realigned) | |
155 | ||
156 | L(hit_limit): | |
157 | mov len, limit | |
158 | RET | |
159 | END (__strnlen) | |
160 | weak_alias (__strnlen, strnlen) | |
161 | libc_hidden_def (strnlen) |