A computer digital logic circuit utilizing an encoded Read Only Memory (ROM) and multiplexor elements is used to translate top-level shift control signals, such as arise from instruction translation, into the low-level control of selecting data input to, and controlling the shift count in, a shif matrix...http://www.google.de/patents/US4484276?utm_source=gb-gplus-sharePatent US4484276 - Shift matrix preselector control circuit
