Re: [Boost-bugs] [Boost C++ Libraries] #11102: gmp_float backend with variable precision does not have distributive property

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #11102: gmp_float backend with variable precision does not have distributive property
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-03-12 07:04:05

#11102: gmp_float backend with variable precision does not have distributive
property
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  Reporter:  Tobias Beck <Tobias.Beck@…>  |      Owner:  johnmaddock
      Type:  Bugs                         |     Status:  closed
 Milestone:  To Be Determined             |  Component:  multiprecision
   Version:  Boost 1.57.0                 |   Severity:  Problem
Resolution:  invalid                      |   Keywords:
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Comment (by Tobias Beck <Tobias.Beck@…>):

 Maybe this is due to a misunderstanding on what "variable precision"
 means? I assumed, that variable precision means that the number of bits is
 extended to fit any result as long as we only apply multiplications,
 subtractions and additions. In this case the distributive law should hold
 independently of the initialization method.

 In fact, I even assumed that internally a fractional representation is
 chosen to cope with the case of divisions. std::numeric_limits shows an
 epsilon of 0.0. I interpreted this as "values are represented exactly"
 (ok, at least w.r.t. certain simple operations).

 In any case, maybe the term "variable precision" needs some
 clarification... What can we expect of a variable precision variable? Is
 there only a very intransparent internal way of choosing the bitness? In
 this case, the type is probably useless, isn't it?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11102#comment:3>
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