e2022a26d0
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@11967 a1c6a512-1295-4272-9138-f99709370657
107 lines
3.4 KiB
ArmAsm
107 lines
3.4 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) 2004 by Jens Arnold
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*
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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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 _memset
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.type _memset,@function
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/* Fills a memory region with specified byte value
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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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* r5 - data
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* r6 - length
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*
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* return value:
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* r0 - start address (like ANSI version)
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*
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* register usage:
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* r0 - temporary
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* r1 - start address +11 for main loop
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* r4 - start address
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* r5 - data (spread to all 4 bytes when using long stores)
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* r6 - current address (runs down from end to start)
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*
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* The instruction order below is devised in a way to utilize the pipelining
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* of the SH1 to the max. The routine fills memory from end to start in
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* order to utilize the auto-decrementing store instructions.
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*/
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_memset:
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neg r4,r0
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and #3,r0 /* r0 = (4 - align_offset) % 4 */
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add #4,r0
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cmp/hs r0,r6 /* at least one aligned longword to fill? */
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add r4,r6 /* r6 = end_address */
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bf .no_longs /* no, jump directly to byte loop */
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extu.b r5,r5 /* start: spread data to all 4 bytes */
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swap.b r5,r0
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or r0,r5 /* data now in 2 lower bytes of r5 */
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swap.w r5,r0
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or r0,r5 /* data now in all 4 bytes of r5 */
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mov r6,r0
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tst #3,r0 /* r0 already long aligned? */
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bt .end_b1 /* yes: skip loop */
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/* leading byte loop: sets 0..3 bytes */
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.loop_b1:
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mov.b r5,@-r0 /* store byte */
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tst #3,r0 /* r0 long aligned? */
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bf .loop_b1 /* runs r0 down until long aligned */
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mov r0,r6 /* r6 = last long bound */
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nop /* keep alignment */
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.end_b1:
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mov r4,r1 /* r1 = start_address... */
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add #11,r1 /* ... + 11, combined for rounding and offset */
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xor r1,r0
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tst #4,r0 /* bit 2 tells whether an even or odd number of */
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bf .loop_odd /* longwords to set */
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/* main loop: set 2 longs per pass */
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.loop_2l:
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mov.l r5,@-r6 /* store first long */
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.loop_odd:
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cmp/hi r1,r6 /* runs r6 down to first long bound */
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mov.l r5,@-r6 /* store second long */
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bt .loop_2l
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.no_longs:
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cmp/hi r4,r6 /* any bytes left? */
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bf .end_b2 /* no: skip loop */
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/* trailing byte loop */
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.loop_b2:
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mov.b r5,@-r6 /* store byte */
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cmp/hi r4,r6 /* runs r6 down to the start address */
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bt .loop_b2
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.end_b2:
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rts
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mov r4,r0 /* return start address */
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.end:
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.size _memset,.end-_memset
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