Apparatus, useful in signal processing, and which can be used for modulo (2.sup.n -1) addition, subtraction, coding, and decoding, has a plurality of 2n input means: n means for receiving a signal I.sub.0, I. sub.1, . . . , I.sub.n-1, and another n means for receiving a signal J. sub.0, J.sub.1, . . ., J.sub.n-1. A pluraity n of means, connected to the n I signal input means, may switch each input means so that it is connected alternately into one of two connecting points, a first and a second connecting point. A plurality n of means is connected to the n first connecting points, for inverting the polarity of a signal received at its input, the output of the inverting means being connected to its associated second connecting point. A plurality n of three input adding means, has one input connected to the output of the inverting means, and another being connected to an associated means for receiving a J signal, the means adding the two inputs. The plurality n of adding means are circularly connected to each other, by a third input in the manner of a full adder. Means, having its n inputs connected to the n adding means, add the n-inputs in an AND manner. A second means, whose input is connected to the output of the n-input adding means, inverts the signal at its input.PPA plurality of two-input means has one of its inputs connected to the output of one of the plurality of n adding means, the other input being connected to the output of the second-named inverting means, the output being the required decoded signal.
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