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/* a-memset.s -- memset, optimised for fido asm

 *

 * Copyright (c) 2007 mocom software GmbH & Co KG)

 *

 * The authors hereby grant permission to use, copy, modify, distribute,

 * and license this software and its documentation for any purpose, provided

 * that existing copyright notices are retained in all copies and that this

 * notice is included verbatim in any distributions. No written agreement,

 * license, or royalty fee is required for any of the authorized uses.

 * Modifications to this software may be copyrighted by their authors

 * and need not follow the licensing terms described here, provided that

 * the new terms are clearly indicated on the first page of each file where

 * they apply.

 */

#include "m68kasm.h"

        .text

        .align  4

        .globl  SYM(memset)

        .type   SYM(memset), @function

|   memset, optimised

|

|   strategy:

|       - no argument testing (the original memcpy from the GNU lib does

|         no checking either)

|       - make sure the destination pointer (the write pointer) is long word

|         aligned. This is the best you can do, because writing to unaligned

|         addresses can be the most costfull thing one could do.

|       - we fill long word wise if possible

|

|   VG, 2006

|

|       bugfixes:

|               - distribution of byte value improved - in cases someone gives

|         non-byte value

|               - residue byte transfer was not working

|

|       VG, April 2007

|

SYM(memset):

        move.l  4(sp),a0        | dest ptr

        move.l  8(sp),d0        | value

        move.l  12(sp),d1       | len

        cmp.l   #16,d1

        blo     .Lbset          | below, byte fills

        |

        move.l  d2,-(sp)        | need a register

        move.b  d0,d2           | distribute low byte to all byte in word

        lsl.l   #8,d0

        move.b  d2,d0

        move.w  d0,d2

        swap    d0              | rotate 16

        move.w  d2,d0

        |

        move.l  a0,d2           | copy of src

        neg.l   d2              | 1 2 3 ==> 3 2 1

        and.l   #3,d2

        beq     2f              | is aligned

        |

        sub.l   d2,d1           | fix length

        lsr.l   #1,d2           | word align needed?

        bcc     1f

        move.b  d0,(a0)+        | fill byte

1:

        lsr.l   #1,d2           | long align needed?

        bcc     2f

        move.w  d0,(a0)+        | fill word

2:

        move.l  d1,d2           | number of long transfers (at least 3)

        lsr.l   #2,d2

        subq.l  #1,d2

1:

        move.l  d0,(a0)+        | fill long words

.Llset:

#if !defined (__mcoldfire__)

        dbra    d2,1b           | loop until done

        sub.l   #0x10000,d2

#else

        subq.l  #1,d2

#endif

        bpl     1b

        and.l   #3,d1           | residue byte transfers, fixed

        move.l  (sp)+,d2        | restore d2

        bra     .Lbset

1:

        move.b  d0,(a0)+        | fill residue bytes

.Lbset:

#if !defined (__mcoldfire__)

        dbra    d1,1b           | loop until done

#else

        subq.l  #1,d1

        bpl     1b

#endif

        move.l  4(sp),d0        | return value

        rts