source: trunk/minix/lib/i386/string/_memmove.s@ 11

!       _memmove()                                      Author: Kees J. Bot
!                                                               2 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
        .align  16
__memmove:
        push    ebp
        mov     ebp, esp
        push    esi
        push    edi
        mov     edi, 8(ebp)     ! String s1
        mov     esi, 12(ebp)    ! String s2
        mov     ecx, 16(ebp)    ! Length
        mov     eax, edi
        sub     eax, esi
        cmp     eax, ecx
        jb      downwards       ! if (s2 - s1) < n then copy downwards
__memcpy:
        cld                     ! Clear direction bit: upwards
        cmp     ecx, 16
        jb      upbyte          ! Don't bother being smart with short arrays
        mov     eax, esi
        or      eax, edi
        testb   al, 1
        jnz     upbyte          ! Bit 0 set, use byte copy
        testb   al, 2
        jnz     upword          ! Bit 1 set, use word copy
uplword:shrd    eax, ecx, 2     ! Save low 2 bits of ecx in eax
        shr     ecx, 2
        rep
        movs                    ! Copy longwords.
        shld    ecx, eax, 2     ! Restore excess count
upword: shr     ecx, 1
        rep
    o16 movs                    ! Copy words
        adc     ecx, ecx        ! One more byte?
upbyte: rep
        movsb                   ! Copy bytes
done:   mov     eax, 8(ebp)     ! Absolutely noone cares about this value
        pop     edi
        pop     esi
        pop     ebp
        ret

! Handle bad overlap by copying downwards, don't bother to do word copies.
downwards:
        std                     ! Set direction bit: downwards
        lea     esi, -1(esi)(ecx*1)
        lea     edi, -1(edi)(ecx*1)
        rep
        movsb                   ! Copy bytes
        cld
        jmp     done