source: trunk/minix/lib/i86/string/memset.s@ 9

!       memset()                                        Author: Kees J. Bot
!                                                               27 Jan 1994
.sect .text; .sect .rom; .sect .data; .sect .bss

! void *memset(void *s, int c, size_t n)
!       Set a chunk of memory to the same byte value.
!
.sect .text
.define _memset
_memset:
        push    bp
        mov     bp, sp
        push    di
        mov     di, 4(bp)       ! The string
        movb    al, 6(bp)       ! The fill byte
        mov     cx, 8(bp)       ! Length
        cld
        cmp     cx, #16
        jb      sbyte           ! Don't bother being smart with short arrays
        test    di, #1
        jnz     sbyte           ! Bit 0 set, use byte store
sword:  movb    ah, al          ! One byte to two bytes
        sar     cx, #1
    rep stos                    ! Store words
        adc     cx, cx          ! One more byte?
sbyte:
    rep stosb                   ! Store bytes
done:   mov     ax, 4(bp)       ! Return some value you have no need for
        pop     di
        pop     bp
        ret