/* Copyright (C) 1998 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 <http://www.gnu.org/licenses/>. */ #include <features.h> #include <endian.h> #include <sys/syscall.h> #include <bits/arm_asm.h> /* size_t strlen(const char *S) * entry: r0 -> string * exit: r0 = len */ .text .global strlen .type strlen,%function .align 4 #if defined(THUMB1_ONLY) /* A simple implementation for when the ARM implementation can't be used. */ .thumb_func strlen: mov r2, #0 1: ldrb r1, [r0, r2] add r2, r2, #1 cmp r1, #0 bne 1b sub r0, r2, #1 bx lr #else 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 #if __BYTE_ORDER == __BIG_ENDIAN orr r2, r2, $0xff000000 @ set this byte to non-zero subs r3, r3, $1 @ any more to do? IT(t, gt) orrgt r2, r2, $0x00ff0000 @ if so, set this byte subs r3, r3, $1 @ more? IT(t, gt) 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? IT(t, gt) orrgt r2, r2, $0x0000ff00 @ if so, set this byte subs r3, r3, $1 @ more? IT(t, gt) orrgt r2, r2, $0x00ff0000 @ then set. #endif Laligned: @ here, we have a word in r2. Does it tst r2, $0x000000ff @ contain any zeroes? IT(tttt, ne) tstne r2, $0x0000ff00 @ tstne r2, $0x00ff0000 @ tstne r2, $0xff000000 @ addne r0, r0, $4 @ if not, the string is 4 bytes longer IT(t, ne) ldrne r2, [r1], $4 @ and we continue to the next word bne Laligned @ Llastword: @ drop through to here once we find a #if __BYTE_ORDER == __BIG_ENDIAN tst r2, $0xff000000 @ word that has a zero byte in it IT(tttt, ne) 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 IT(t, ne) addne r0, r0, $1 @ must be zero) #else tst r2, $0x000000ff @ IT(tttt, ne) 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 IT(t, ne) addne r0, r0, $1 @ must be zero) #endif #if defined(__USE_BX__) bx lr #else mov pc,lr #endif #endif .size strlen,.-strlen libc_hidden_def(strlen)