Device and method for computing function value of function

A device (10) for computing a function value of a function F comprises a memory (18), a truncator unit (14), a selector unit (16), and an evaluator unit (20). The memory (18) contains a look-up table (19) comprising a set of entries (L1; L2; L3; L4), each of which entries having associated with it a domain (D1; D2; D3; D4) and an approximation function (F1; F2; F3; F4) for approximating the function F on the associated domain. The truncator unit (14) is arranged to truncate or round a first value X1 to generate a second value X2. The selector unit (16) is arranged to select an entry (L1; L2; L3; L4) of the lookup-table (19) according to the second value X2, thus selecting the approximation function (F1; F2; F3; F4) that is associated with the selected entry. The evaluator unit (20) is arranged to determine the function value of the selected approximation function (F1; F2; F3; F4) at the first value X1. The device (10) may be integrated in a digital signal processor (DSP). A method for computing a function val