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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2010 Nils Wallménius
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
/* size_t strlen(const char *str) */
.section .text,"ax",@progbits
.align 2
.globl strlen
.type strlen, @function
strlen:
move.l 4(%sp), %a0 /* %a0 = *str */
move.l %a0, %a1 /* %a1 = start address */
move.l %a0, %d0
andi.l #3, %d0 /* %d0 = %a0 & 3 */
beq.b 1f /* already aligned */
jmp.l (-2,%pc,%d0.l*4)
tst.b (%a0)+
beq.b .done
tst.b (%a0)+
beq.b .done
tst.b (%a0)+
beq.b .done
1:
move.l (%a0)+, %d0 /* load %d0 increment %a0 */
/* use trick to test the whole word for null bytes */
move.l %d0, %d1
subi.l #0x01010101, %d1
not.l %d0
and.l %d1, %d0
andi.l #0x80808080, %d0
beq.b 1b /* if the test was false repeat */
/* ok, so the last word contained a 0 byte, test individual bytes */
subq.l #4, %a0
tst.b (%a0)+
beq.b .done
tst.b (%a0)+
beq.b .done
tst.b (%a0)+
beq.b .done
/* last byte must be 0 so we don't need to load it, so we don't increment a0
so we jump past the subq instr */
.word 0x51fa /* trapf.w, shadow next instr */
.done:
subq.l #1, %a0 /* %a0 is 1 too large due to the last increment */
sub.l %a1, %a0 /* how many times did we repeat? */
move.l %a0, %d0 /* return value in %d0 */
rts
.size strlen, .-strlen
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