96 lines
3.3 KiB
ArmAsm
96 lines
3.3 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) 2005 by Jens Arnold
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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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#include "config.h"
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.section .icode,"ax",@progbits
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.align 2
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.global _strlen
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.type _strlen,@function
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/* Works out the length of a string
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* This version is optimized for speed
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*
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* arguments:
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* r4 - start address
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*
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* return value:
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* r0 - string length
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*
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* register usage:
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* r0 - current address
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* r1 - current value (byte/long)
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* r2 - mask for alignment / zero (for cmp/str)
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* r4 - start address
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*
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*/
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_strlen:
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mov r4,r0 /* r0 = start address */
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tst #3,r0 /* long aligned? */
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bt .start_l /* yes, jump directly to the longword loop */
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/* not long aligned: check the first 3 bytes */
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mov.b @r0+,r1 /* fetch first byte */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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mov.b @r0+,r1 /* fetch second byte */
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mov #3,r2 /* prepare mask: r2 = 0..00000011b */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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mov.b @r0+,r1 /* fetch third byte */
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not r2,r2 /* prepare mask: r2 = 1..11111100b */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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/* not yet found, fall through into longword loop */
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and r2,r0 /* align down to long bound */
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/* main loop: check longwords */
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.start_l:
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mov #0,r2 /* zero longword for cmp/str */
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.loop_l:
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mov.l @r0+,r1 /* fetch long word */
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cmp/str r1,r2 /* any zero byte within? */
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bf .loop_l /* no, loop */
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add #-4,r0 /* set address back to start of this longword */
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/* the last longword contains the string end: figure out the byte */
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mov.b @r0+,r1 /* fetch first byte */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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mov.b @r0+,r1 /* fetch second byte */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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mov.b @r0+,r1 /* fetch third byte */
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tst r1,r1 /* byte == 0 ? */
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bt .hitzero /* yes, string end found */
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rts /* must be the fourth byte */
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sub r4,r0 /* len = string_end - string_start */
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.hitzero:
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add #-1,r0 /* undo address increment */
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rts
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sub r4,r0 /* len = string_end - string_start */
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.end:
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.size _strlen,.end-_strlen
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