An electroweak library for the calculation of EWRC to $e^{+}e^{-} \to f\overline{f}$ within the CalcPHEP project

We present a description of calculations of the electroweak amplitude for e+ e- --> t tbar process. The calculations are done within OMS renormalization scheme in two gauges: Rxi, which allows to explicitly control gauge invariance by examining cancellation of gauge parameters and search for gauge invariant subsets of diagrams; and in the unitary gauge as a cross-check. The formulae derived are realized in a FORTRAN code which is being created within the framework of the project topfit --- successor of ZFITTER. We present a comprehensive comparison between topfit results for the light top with corresponding ZFITTER results for u ubar channel, as well as a preliminary comparison with existing in the world literature results.