tree 686df7908dddc39f50570aeadc0b2075a3b184aa
parent dda70fca7979d86e04bba9ba5bad32162327550c
author Tom Tsou <tom.tsou@ettus.com> 1479990272 +0700
committer Tom Tsou <tom@tsou.cc> 1491870968 +0000

core/conv: implement optimized Viterbi decoder

Add a separate, faster convolution decoding implementation for rates
up to N=4 and constraint lengths of K=5 and K=7, which covers the
most GSM code uses. The decoding algorithm exploits the symmetric
structure of the Viterbi add-compare-select (ACS) operation - commonly
known as the ACS butterfly. This shift-register optimization can be
found in the well-known text by Dave Forney.

Forney, G.D., "The Viterbi Algorithm," Proc. of the IEEE, March 1973.

Implementation is non-architecture specific and improves performance on
x86 as well as ARM processors. Existing API is unchanged with optimized
code being called internally for supported codes.

The original code was relicensed under GPLv2-or-later with permission
of copyright holder - Tom Tsou.

Change-Id: I74d355274b4176a7d924f91ef3c96912ce338fb2