We present a novel lossless universal source coding algorithm that uses
parallel computational units to increase the throughput. The length-N input
sequence is partitioned into B blocks. Processing each block independently of
the other blocks can accelerate the computation by a factor of B, but
degrades the compression quality. Instead, our approach is to first estimate
the minimum description length (MDL) source underlying the entire input, and
then encode each of the B blocks in parallel based on the MDL source. With
this two-pass approach, the compression loss incurred by using more parallel
units is insignificant. Our algorithm is work-efficient, i.e., its
computational complexity is O(N/B). Its redundancy is approximately
Blog(N/B) bits above Rissanen's lower bound on universal coding performance,
with respect to any tree source whose maximal depth is at most log(N/B)
