give a logical signal
losig_list *givelosig(ptfig, index)
Pointer to the figure in which the signal should be seeked or created
Index of the signal to find or create
givelosig looks in the list of signals of the logical model pointed
to by ptfig for a signal identified by its index. If this signal
exists, then its pointer is returned, else, the signal is created, with
direction, DIR, UNKNOWN, and TYPE INTERNAL, and, of
course INDEX index, and the pointer is returned.
givelosig returns a pointer to the signal.
losig_list *give_sig_by_name(figname, index)
/* never fails */
return givelosig(getlofig(figname), index);