id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
3969,position_to_offset() is broken for Microsoft Visual C++/Dinkumware,gareth.sylvester-bradley@…,Daniel James,"I have found a bug in position_to_offset() on Microsoft Visual C++/Dinkumware demonstrated by the following test app –

{{{
#include <iostream>
#include <boost/iostreams/positioning.hpp>

int main( int, char*[] )
{
  const boost::int64_t twoGB = 2 << 30;
  std::streampos pos = boost::iostreams::offset_to_position( twoGB );
  pos -= 2;
  if ( twoGB - 2 != boost::iostreams::position_to_offset( pos ) )
  {
    std::cout << ""Failed!"" << std::endl;
    return -1;
  }

  return 0;
}
}}}

This is resolved by the following patch to boost/iostreams/positioning.hpp.

{{{
105,106c105,106
<            static_cast<stream_offset>(static_cast<std::streamoff>(pos)) -
<            static_cast<stream_offset>(_FPOSOFF(streampos_to_fpos_t(pos)));
---
>            static_cast<stream_offset>(static_cast<std::streamoff>(pos) -
>                                       _FPOSOFF(streampos_to_fpos_t(pos)));
}}}

This has the potential to affect many parts of Boost.Iostreams but in particular it means the ""small seeks optimization"" in indirect_streambuf.hpp is broken.
",Patches,closed,Boost 1.43.0,iostreams,Boost 1.42.0,Problem,fixed,,