aa1e471f9a
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@25968 a1c6a512-1295-4272-9138-f99709370657
71 lines
2.4 KiB
ArmAsm
71 lines
2.4 KiB
ArmAsm
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2010 Nils Wallménius
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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/* size_t strlen(const char *str) */
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.section .text,"ax",@progbits
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.align 2
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.globl strlen
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.type strlen, @function
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strlen:
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move.l 4(%sp), %a0 /* %a0 = *str */
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move.l %a0, %a1 /* %a1 = start address */
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move.l %a0, %d0
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andi.l #3, %d0 /* %d0 = %a0 & 3 */
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beq.b 1f /* already aligned */
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jmp.l (-2,%pc,%d0.l*4)
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tst.b (%a0)+
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beq.b .done
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tst.b (%a0)+
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beq.b .done
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tst.b (%a0)+
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beq.b .done
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1:
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move.l (%a0)+, %d0 /* load %d0 increment %a0 */
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/* use trick to test the whole word for null bytes */
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move.l %d0, %d1
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subi.l #0x01010101, %d1
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not.l %d0
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and.l %d1, %d0
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andi.l #0x80808080, %d0
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beq.b 1b /* if the test was false repeat */
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/* ok, so the last word contained a 0 byte, test individual bytes */
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subq.l #4, %a0
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tst.b (%a0)+
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beq.b .done
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tst.b (%a0)+
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beq.b .done
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tst.b (%a0)+
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beq.b .done
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/* last byte must be 0 so we don't need to load it, so we don't increment a0
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so we jump past the subq instr */
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.word 0x51fa /* trapf.w, shadow next instr */
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.done:
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subq.l #1, %a0 /* %a0 is 1 too large due to the last increment */
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sub.l %a1, %a0 /* how many times did we repeat? */
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move.l %a0, %d0 /* return value in %d0 */
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rts
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.size strlen, .-strlen
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