1 /* Copyright (C) 1998-2015 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 <http://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
34 ldr r2, [\B], $4 @ get the first word
35 ands r3, r0, $3 @ how many bytes are duff?
36 rsb r0, r3, $0 @ get - that number into counter.
37 beq Laligned @ skip into main check routine if no
40 orr r2, r2, $0xff000000 @ set this byte to non-zero
41 subs r3, r3, $1 @ any more to do?
42 orrgt r2, r2, $0x00ff0000 @ if so, set this byte
43 subs r3, r3, $1 @ more?
44 orrgt r2, r2, $0x0000ff00 @ then set.
46 orr r2, r2, $0x000000ff @ set this byte to non-zero
47 subs r3, r3, $1 @ any more to do?
48 orrgt r2, r2, $0x0000ff00 @ if so, set this byte
49 subs r3, r3, $1 @ more?
50 orrgt r2, r2, $0x00ff0000 @ then set.
52 Laligned: @ here, we have a word in r2. Does it
53 tst r2, $0x000000ff @ contain any zeroes?
54 tstne r2, $0x0000ff00 @
55 tstne r2, $0x00ff0000 @
56 tstne r2, $0xff000000 @
57 addne r0, r0, $4 @ if not, the string is 4 bytes longer
59 ldrne r2, [\B], $4 @ and we continue to the next word
61 Llastword: @ drop through to here once we find a
63 tst r2, $0xff000000 @ word that has a zero byte in it
65 tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
67 tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
68 addne r0, r0, $1 @ must be zero)
70 tst r2, $0x000000ff @ word that has a zero byte in it
72 tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
74 tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
75 addne r0, r0, $1 @ must be zero)
79 libc_hidden_builtin_def (strlen)