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f5ad94e0 | 1 | /* strlen -- find the length of a nul-terminated string. |
688903eb | 2 | Copyright (C) 2013-2018 Free Software Foundation, Inc. |
f5ad94e0 RH |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library. If not, see | |
17 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <sysdep.h> | |
20 | ||
21 | .syntax unified | |
22 | .text | |
23 | ||
24 | ENTRY (strlen) | |
25 | @ r0 = start of string | |
81cb7a0b | 26 | ldrb r2, [r0] @ load the first byte asap |
f5ad94e0 RH |
27 | |
28 | @ To cater to long strings, we want to search through a few | |
29 | @ characters until we reach an aligned pointer. To cater to | |
30 | @ small strings, we don't want to start doing word operations | |
31 | @ immediately. The compromise is a maximum of 16 bytes less | |
32 | @ whatever is required to end with an aligned pointer. | |
33 | @ r3 = number of characters to search in alignment loop | |
34 | and r3, r0, #7 | |
35 | mov r1, r0 @ Save the input pointer | |
36 | rsb r3, r3, #15 @ 16 - 1 peeled loop iteration | |
37 | cmp r2, #0 | |
38 | beq 99f | |
39 | ||
40 | @ Loop until we find ... | |
81cb7a0b | 41 | 1: ldrb r2, [r0, #1]! |
f5ad94e0 RH |
42 | subs r3, r3, #1 @ ... the aligment point |
43 | it ne | |
44 | cmpne r2, #0 @ ... or EOS | |
45 | bne 1b | |
46 | ||
47 | @ Disambiguate the exit possibilites above | |
48 | cmp r2, #0 @ Found EOS | |
49 | beq 99f | |
50 | add r0, r0, #1 | |
51 | ||
52 | @ So now we're aligned. | |
81cb7a0b | 53 | ldrd r2, r3, [r0], #8 |
f5ad94e0 RH |
54 | #ifdef ARCH_HAS_T2 |
55 | movw ip, #0x0101 | |
81cb7a0b | 56 | pld [r0, #64] |
f5ad94e0 RH |
57 | movt ip, #0x0101 |
58 | #else | |
59 | ldr ip, =0x01010101 | |
81cb7a0b | 60 | pld [r0, #64] |
f5ad94e0 RH |
61 | #endif |
62 | ||
63 | @ Loop searching for EOS, 8 bytes at a time. | |
64 | @ Subtracting (unsigned saturating) from 1 for any byte means that | |
65 | @ we get 1 for any byte that was originally zero and 0 otherwise. | |
66 | @ Therefore we consider the lsb of each byte the "found" bit. | |
67 | .balign 16 | |
68 | 2: uqsub8 r2, ip, r2 @ Find EOS | |
69 | uqsub8 r3, ip, r3 | |
81cb7a0b | 70 | pld [r0, #128] @ Prefetch 2 lines ahead |
f5ad94e0 RH |
71 | orrs r3, r3, r2 @ Combine the two words |
72 | it eq | |
81cb7a0b | 73 | ldrdeq r2, r3, [r0], #8 |
f5ad94e0 RH |
74 | beq 2b |
75 | ||
76 | @ Found something. Disambiguate between first and second words. | |
77 | @ Adjust r0 to point to the word containing the match. | |
78 | @ Adjust r2 to the found bits for the word containing the match. | |
79 | cmp r2, #0 | |
80 | sub r0, r0, #4 | |
81 | ite eq | |
82 | moveq r2, r3 | |
83 | subne r0, r0, #4 | |
84 | ||
85 | @ Find the bit-offset of the match within the word. Note that the | |
86 | @ bit result from clz will be 7 higher than "true", but we'll | |
87 | @ immediately discard those bits converting to a byte offset. | |
88 | #ifdef __ARMEL__ | |
89 | rev r2, r2 @ For LE, count from the little end | |
90 | #endif | |
91 | clz r2, r2 | |
92 | add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte | |
93 | 99: | |
94 | sub r0, r0, r1 @ Subtract input to compute length | |
95 | bx lr | |
96 | ||
97 | END (strlen) | |
98 | ||
99 | libc_hidden_builtin_def (strlen) |