1 /* Copyright (C) 1998 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/>. */
21 #include <bits/arm_asm.h>
22 #include <bits/arm_bx.h>
24 /* size_t strlen(const char *S)
31 .type strlen,%function
34 #if defined(THUMB1_ONLY)
35 /* A simple implementation for when the ARM implementation can't be used. */
48 bic r1, r0, $3 @ addr of word containing first byte
49 ldr r2, [r1], $4 @ get the first word
50 ands r3, r0, $3 @ how many bytes are duff?
51 rsb r0, r3, $0 @ get - that number into counter.
52 beq Laligned @ skip into main check routine if no
54 #if __BYTE_ORDER == __BIG_ENDIAN
55 orr r2, r2, $0xff000000 @ set this byte to non-zero
56 subs r3, r3, $1 @ any more to do?
58 orrgt r2, r2, $0x00ff0000 @ if so, set this byte
59 subs r3, r3, $1 @ more?
61 orrgt r2, r2, $0x0000ff00 @ then set.
63 orr r2, r2, $0x000000ff @ set this byte to non-zero
64 subs r3, r3, $1 @ any more to do?
66 orrgt r2, r2, $0x0000ff00 @ if so, set this byte
67 subs r3, r3, $1 @ more?
69 orrgt r2, r2, $0x00ff0000 @ then set.
71 Laligned: @ here, we have a word in r2. Does it
72 tst r2, $0x000000ff @ contain any zeroes?
74 tstne r2, $0x0000ff00 @
75 tstne r2, $0x00ff0000 @
76 tstne r2, $0xff000000 @
77 addne r0, r0, $4 @ if not, the string is 4 bytes longer
79 ldrne r2, [r1], $4 @ and we continue to the next word
81 Llastword: @ drop through to here once we find a
82 #if __BYTE_ORDER == __BIG_ENDIAN
83 tst r2, $0xff000000 @ word that has a zero byte in it
86 tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
88 tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
90 addne r0, r0, $1 @ must be zero)
95 tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
97 tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
99 addne r0, r0, $1 @ must be zero)
104 .size strlen,.-strlen
106 libc_hidden_def(strlen)