Re: [Boost-bugs] [Boost C++ Libraries] #12327: cpp_rational::convert_to<double>() does not return the nearest number

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12327: cpp_rational::convert_to<double>() does not return the nearest number
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-07-14 17:00:01

#12327: cpp_rational::convert_to<double>() does not return the nearest number
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  Reporter:  komakisen@…       |      Owner:  johnmaddock
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  multiprecision
   Version:  Boost 1.61.0      |   Severity:  Problem
Resolution:                    |   Keywords:
-------------------------------+----------------------------

Comment (by johnmaddock):

 I believe it's an error in your test program, taking the first example:

 0.099999999999999992 = 7205759403792793/72057594037927936
 0.10000000000000001  = 3602879701896397/36028797018963968

 Note that these fractions are exact (in the binary, not decimal sense).

 Then r112 becomes 5404319552844595/54043195528445952 which is
 0.0999999999999999962992565845828115319212277730305989583... in decimal,
 which rounds up to 0.10000000000000001 and not down to
 0.099999999999999992 due to the "6" after the string of 9's.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12327#comment:1>
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