  We present solidfmm, a highly optimised C++ library for the solid harmonics
as they are needed in fast multipole methods. The library provides efficient,
vectorised implementations of the translation operations M2M, M2L, and L2L, and
is available as free software. While asymptotically of complexity $O(P^3)$, for
all practically relevant expansion orders, the translation operators display an
empirical complexity of $O(P^2)$, outperforming the na\"ive implementation by
orders of magnitude.
