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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