1 /* Copyright (C) 1998-2020 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Code contributed by Matthew Wilcox <willy@odie.barnet.ac.uk>
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.
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.
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 <https://www.gnu.org/licenses/>. */
19 /* Thumb requires excessive IT insns here. */
23 /* size_t strlen(const char *S)
32 bic r1, r0, $3 @ addr of word containing first byte
33 ldr r2, [r1], $4 @ get the first word
34 ands r3, r0, $3 @ how many bytes are duff?
35 rsb r0, r3, $0 @ get - that number into counter.
36 beq Laligned @ skip into main check routine if no
39 orr r2, r2, $0xff000000 @ set this byte to non-zero
40 subs r3, r3, $1 @ any more to do?
41 orrgt r2, r2, $0x00ff0000 @ if so, set this byte
42 subs r3, r3, $1 @ more?
43 orrgt r2, r2, $0x0000ff00 @ then set.
45 orr r2, r2, $0x000000ff @ set this byte to non-zero
46 subs r3, r3, $1 @ any more to do?
47 orrgt r2, r2, $0x0000ff00 @ if so, set this byte
48 subs r3, r3, $1 @ more?
49 orrgt r2, r2, $0x00ff0000 @ then set.
51 Laligned: @ here, we have a word in r2. Does it
52 tst r2, $0x000000ff @ contain any zeroes?
53 tstne r2, $0x0000ff00 @
54 tstne r2, $0x00ff0000 @
55 tstne r2, $0xff000000 @
56 addne r0, r0, $4 @ if not, the string is 4 bytes longer
57 ldrne r2, [r1], $4 @ and we continue to the next word
59 Llastword: @ drop through to here once we find a
61 tst r2, $0xff000000 @ word that has a zero byte in it
63 tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
65 tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
66 addne r0, r0, $1 @ must be zero)
68 tst r2, $0x000000ff @ word that has a zero byte in it
70 tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
72 tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
73 addne r0, r0, $1 @ must be zero)
77 libc_hidden_builtin_def (strlen)