Re: [Boost-bugs] [Boost C++ Libraries] #12527: cpp_bin_float: Anal fixation. Part 3. Double rounding when result of convert_to<double>() is a subnormal

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12527: cpp_bin_float: Anal fixation. Part 3. Double rounding when result of convert_to<double>() is a subnormal
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-11-08 19:45:00

#12527: cpp_bin_float: Anal fixation. Part 3. Double rounding when result of
convert_to<double>() is a subnormal
-------------------------------+----------------------------
  Reporter:  Michael Shatz     |      Owner:  johnmaddock
      Type:  Bugs              |     Status:  reopened
 Milestone:  To Be Determined  |  Component:  multiprecision
   Version:  Boost 1.62.0      |   Severity:  Problem
Resolution:                    |   Keywords:
-------------------------------+----------------------------

Comment (by johnmaddock):

 Right the case denorm_min()/2 is the only one with that exponent that
 doesn't round up, I though I had this tested already but apparently not.
 The fix is trivial, but in the process of generating tests there are two
 other issues:

 * When we add numeric_limits::min() we may loose important digits (that
 would otherwise break a tie).
 * When we add numeric_limits::min() we may round up, leading to double
 rounding again (or at least that's what I think is happening).

 I may need to just bite the bullet and write a custom conversion
 routine...

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12527#comment:8>
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