Re: [Boost-bugs] [Boost C++ Libraries] #3030: [crc] optimization of crc_optimal::process_block

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #3030: [crc] optimization of crc_optimal::process_block
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-12-16 05:59:16

#3030: [crc] optimization of crc_optimal::process_block
-------------------------------+--------------------------------------------
  Reporter:  qehgt0@…          |       Owner:  dlwalker    
      Type:  Patches           |      Status:  new         
 Milestone:  Boost 1.40.0      |   Component:  crc         
   Version:  Boost 1.39.0      |    Severity:  Optimization
Resolution:                    |    Keywords:  crc         
-------------------------------+--------------------------------------------

Comment (by Vasily Titskiy <qehgt0@…>):

 Compiler is assuming (and it is correct assumption from compiler's point
 of view) that memory location of member variable 'this->rem' can be
 between 'bytes_begin' and 'bytes_end'.

 So, compiler _must_ generate non-optimal code for this loop that always
 stores temporary value of 'rem' variable into memory before processing
 every next byte.

 It should be same or faster on every system.

 I can check it on msvc2008, armv7-gcc3.2/gcc4.6, intel x86/amd64 later, if
 it needed.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3030#comment:3>
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