The general approach to mathematical function implementation consists of three stages: argument reduction, approximation and reconstruction. The argument reduction step is needed to reduce the degree of the approximation polynomial and to simplify the error analysis. For some particular functions (e.g. exp) it is done using its algebraic properties. In the general case the whole domain is split into small subdomains to get low-degree approximation on each of them. Here we present a novel algorithm for the domain splitting that will be integrated soon to Metalibm code generator.