The MDC-1 calculation, which is used in the MDC-4 calculation, consists of this procedure:

MDC-1 (KD1, KD2, IN1, IN2, OUT1, OUT2);
   Set KD1mod := set bit 1 and bit 2 of KD1 to "1" and "0", respectively.
   Set KD2mod := set bit 1 and bit 2 of KD2 to "0" and "1", respectively.
   Set F1 := IN1 XOR eKD1mod(IN1)
   Set F2 := IN2 XOR eKD2mod(IN2)
   Set OUT1 := (bits 0..31 of F1) || (bits 32..63 of F2)
   Set OUT2 := (bits 0..31 of F2) || (bits 32..63 of F1)
End procedure