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Date: Fri, 24 Jan 2003 14:50:26 +0100 (MET)
From: Nick Smith <nick.smith@techop.ch>
Subject: Similarity.encodeNorm() / decodeNorm() funny.
To: lucene-dev@jakarta.apache.org
Reply-to: Nick Smith <nick.smith@techop.ch>
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Hi Luceners,
   I'm (mis)using the field normalisation factor for my own
sorting purposes.  I create a sorting indicator as a byte
value and use Similarity.decodeNorm() to create the float
value suitable and have encounter the following :

I made the assumption that

  encodeNorm(decodeNorm(abyte)) == abyte

i.e. it is reflexive function.

However the assumption is value for values 1-7 (values
-128 to 0 and 1 to 127 are as expected) - see below...

in = 0 float = 0.0 out = 0
in = 1 float = 5.820766E-10 out = 8
in = 2 float = 6.9849193E-10 out = 8
in = 3 float = 8.1490725E-10 out = 8
in = 4 float = 9.313226E-10 out = 8
in = 5 float = 1.1641532E-9 out = 8
in = 6 float = 1.3969839E-9 out = 8
in = 7 float = 1.6298145E-9 out = 8
in = 8 float = 1.8626451E-9 out = 8
in = 9 float = 2.3283064E-9 out = 9

Now that I know of this "feature" I can workaround it
but using only the range 9-127 (which is enough in my
case).

I've posted this because it has caused a mistifying
problem in our product and others _might_ be encountering
the same "feature".

Many Thanks for the work people do on Lucene!!!

Cheers,

Nick


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