  We present a procedure for efficiently compressing astronomical radio data
for high performance applications. Integrated, post-correlation data are first
passed through a nearly lossless rounding step which compares the precision of
the data to a generalized and calibration-independent form of the radiometer
equation. This allows the precision of the data to be reduced in a way that has
an insignificant impact on the data. The newly developed Bitshuffle lossless
compression algorithm is subsequently applied. When the algorithm is used in
conjunction with the HDF5 library and data format, data produced by the CHIME
Pathfinder telescope is compressed to 28% of its original size and
decompression throughputs in excess of 1 GB/s are obtained on a single core.
