source: bootcd/isolinux/syslinux-6.03/dos/memmove.S

#
# memmove.S
#
# Simple 16-bit memmove() implementation
#

        .text
        .code16gcc
        .globl memmove
        .type memmove, @function
memmove:
        pushw %di
        pushw %si
        movw %ax,%di
        movw %dx,%si
        cmpw %si,%di
        ja 1f
        # The third argument is already in cx
        cld
        rep ; movsb
2:
        popw %si
        popw %di
        ret

1:      /* si <= di, need reverse copy */
        add %cx,%di
        add %cx,%si
        dec %di
        dec %si
        std
        rep ; movsb
        cld
        jmp 2b

        .size memmove,.-memmove