• Paul Wilkins's avatar
    Further experimentation with the mode context · a57dbd95
    Paul Wilkins authored
    Experiments with a larger set of contexts and some
    clean up to replace magic numbers regarding the
    number of contexts.
    
    The starting values and rate of backwards adaption
    are still suspect and based on a small set of tests.
    Added forwards adjustment of probabilities.
    
    The net result of adding the new context and forward
    update is small compared to the old context from the
    legacy find_near function.  (down a little on derf but
    up by a similar amount for HD)
    
    HOWEVER.... with the new context and forward update
    the impact of disabling the reverse update (which may be
    necessary in some use cases to facilitate parallel decoding)
    is hugely reduced.
    
    For the old context without forward update, the impact of
    turning off reverse update (Experiment was with SB off) was
    Derf - 0.9, Yt -1.89, ythd -2.75 and sthd -8.35. The impact was
    mainly at low data rates.
    
    With the new context and forward update enabled the impact
    for all the test sets was no more than 0.5-1% (again most at
    the low end).
    
    Change-Id: Ic751b414c8ce7f7f3ebc6f19a741d774d2b4b556
    a57dbd95
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