  Polar codes are a new class of capacity-achieving error-correcting codes with
low encoding and decoding complexity. Their low-complexity decoding algorithms
rendering them attractive for use in software-defined radio applications where
computational resources are limited. In this work, we present low-latency
software polar decoders that exploit modern processor capabilities. We show how
adapting the algorithm at various levels can lead to significant improvements
in latency and throughput, yielding polar decoders that are suitable for
high-performance software-defined radio applications on modern desktop
processors and embedded-platform processors. These proposed decoders have an
order of magnitude lower latency and memory footprint compared to
state-of-the-art decoders, while maintaining comparable throughput. In
addition, we present strategies and results for implementing polar decoders on
graphical processing units. Finally, we show that the energy efficiency of the
proposed decoders is comparable to state-of-the-art software polar decoders.
