| CPC H03K 19/17728 (2013.01) | 15 Claims |

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1. A method, performed in a device and comprising:
applying a pre-function w=P(x) to an input signal x to obtain a first result w; and
applying a look up table (LUT) to the first result w, wherein the LUT represents a main function ƒw(w) defined for a second grid of values Gw such that the pre-function P(x) is piecewise defined on a first grid Gx of signal values, where Gw=P(Gx), and
wherein the pre-function P(x) is obtained from a second pre-function Q(x) by applying Q(x) to signal values x to calculate the second grid Gw=Q(Gx) and defining the pre-function P(x) piecewise on the first grid Gx by linear interpolation of the values of the second grid Gw such that P(Gx)=Q(Gx).
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