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/* Copyright (C) 1998-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Code contributed by Matthew Wilcox <willy@odie.barnet.ac.uk>
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<https://www.gnu.org/licenses/>. */
/* Thumb requires excessive IT insns here. */
#define NO_THUMB
#include <sysdep.h>
/* size_t strlen(const char *S)
* entry: r0 -> string
* exit: r0 = len
*/
.syntax unified
.text
ENTRY(strlen)
bic r1, r0, $3 @ addr of word containing first byte
ldr r2, [r1], $4 @ get the first word
ands r3, r0, $3 @ how many bytes are duff?
rsb r0, r3, $0 @ get - that number into counter.
beq Laligned @ skip into main check routine if no
@ more
#ifdef __ARMEB__
orr r2, r2, $0xff000000 @ set this byte to non-zero
subs r3, r3, $1 @ any more to do?
orrgt r2, r2, $0x00ff0000 @ if so, set this byte
subs r3, r3, $1 @ more?
orrgt r2, r2, $0x0000ff00 @ then set.
#else
orr r2, r2, $0x000000ff @ set this byte to non-zero
subs r3, r3, $1 @ any more to do?
orrgt r2, r2, $0x0000ff00 @ if so, set this byte
subs r3, r3, $1 @ more?
orrgt r2, r2, $0x00ff0000 @ then set.
#endif
Laligned: @ here, we have a word in r2. Does it
tst r2, $0x000000ff @ contain any zeroes?
tstne r2, $0x0000ff00 @
tstne r2, $0x00ff0000 @
tstne r2, $0xff000000 @
addne r0, r0, $4 @ if not, the string is 4 bytes longer
ldrne r2, [r1], $4 @ and we continue to the next word
bne Laligned @
Llastword: @ drop through to here once we find a
#ifdef __ARMEB__
tst r2, $0xff000000 @ word that has a zero byte in it
addne r0, r0, $1 @
tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
addne r0, r0, $1 @
tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
addne r0, r0, $1 @ must be zero)
#else
tst r2, $0x000000ff @ word that has a zero byte in it
addne r0, r0, $1 @
tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
addne r0, r0, $1 @
tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
addne r0, r0, $1 @ must be zero)
#endif
DO_RET(lr)
END(strlen)
libc_hidden_builtin_def (strlen)
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