source: trunk/minix/lib/i86/string/_memmove.s@ 11

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

! void *_memmove(void *s1, const void *s2, size_t n)
!       Copy a chunk of memory.  Handle overlap.
!
.sect .text
.define __memmove, __memcpy
__memmove:
        push    bp
        mov     bp, sp
        push    si
        push    di
        mov     di, 4(bp)       ! String s1
        mov     si, 6(bp)       ! String s2
        mov     cx, 8(bp)       ! Length
        mov     ax, di
        sub     ax, si
        cmp     ax, cx
        jb      downwards       ! if (s2 - s1) < n then copy downwards
__memcpy:
        cld                     ! Clear direction bit: upwards
        cmp     cx, #16
        jb      upbyte          ! Don't bother being smart with short arrays
        mov     ax, si
        or      ax, di
        testb   al, #1
        jnz     upbyte          ! Bit 0 set, use byte copy
upword: shr     cx, #1
    rep movs                    ! Copy words
        adc     cx, cx          ! One more byte?
upbyte:
    rep movsb                   ! Copy bytes
done:   mov     ax, 4(bp)       ! Absolutely noone cares about this value
        pop     di
        pop     si
        pop     bp
        ret

! Handle bad overlap by copying downwards, don't bother to do word copies.
downwards:
        std                     ! Set direction bit: downwards
        add     si, cx
        dec     si
        add     di, cx
        dec     di
    rep movsb                   ! Copy bytes
        cld
        jmp     done