int
do_reverse(arglast)
int *arglast;
{
    STR **st = stack->ary_array;
    register STR **up = &st[arglast[1]];
    register STR **down = &st[arglast[2]];
    register int i = arglast[2] - arglast[1];

    while (i-- > 0) {
	*up++ = *down;
	if (i-- > 0)
	    *down-- = *up;
    }
    i = arglast[2] - arglast[1];
    Move(down+1,up,i/2,STR*);
    return arglast[2] - 1;
}