Algorithm 910: a portable C++ multiple-precision system for special-function calculations. This article presents a portable C++ system for multiple precision calculations of special functions called e_float. It has an extendable architecture with a uniform C++ layer which can be used with any suitably prepared MP type. The system implements many high-precision special functions and extends some of these to very large parameter ranges. It supports calculations with 30...300 decimal digits of precision. Interoperabilities with Microsoft’s ® CLR, Python, and Mathematica ® are supported. The e_float system and its usage are described in detail. Implementation notes, testing results, and performance measurements are provided.