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: 2016-11-14 10:29:08

#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 anonymous):

 Nod.  I started experimenting with an improved version last night - like
 yours it calls ldexp exactly once for float and double conversions (at
 least on 64-bit GCC), and it's *much* faster.  Unfortunately I ran out of
 time before tracking down a few bugs.  There's also a strange issue when
 the bit count is between 65 and 128 when it runs approx 10x slower!  I
 suspect {{{__int128 -> double}}} conversion is the bottleneck, but I'll
 investigate more later in the week.  Other than that, it's more or less
 constant time regardless of the bit count.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12527#comment:16>
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