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[Discuss-gnuradio] [VOLK] 16i_max_star_horizontal_16i non-saturating sub

From: West, Nathan
Subject: [Discuss-gnuradio] [VOLK] 16i_max_star_horizontal_16i non-saturating subtraction
Date: Wed, 5 Feb 2014 10:04:37 -0600

I was doing some work with this kernel and came across an odd result
that I think is caused by a non-saturating add in the generic
proto-kernel, that should also be relevant to the 16i_max_star_16i.

I haven't looked too much in to the SSE versions, but the generic
versions are doing a comparison by subtracting two values and
comparing the result to 0. At least in the QA on armhf this is causing
wrap-around so that the smaller of the two numbers is returned as the

Since I'm pretty sure this is part of the max* operator defined by
Viterbi in his "justification and implementation of a MAP decoder" I
think this result is incorrect unless I'm misunderstanding part of the

Can somebody with a little more insight in to this kernel ping back if
this is intended behavior? If not, is there some benefit to doing
(x-y)>0 vs x>y as the comparison?


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