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The Windows Access Control Model: Part 2

, 27 Jun 2005
This second part of the Access Control series will program with the basic Access Control structures.
boost.zip
boost
config
compiler
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stdlib
detail
mpl
aux_
config
preprocessed
bcc
bcc551
gcc
msvc60
msvc70
mwcw
no_ctps
no_ttp
plain
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range_c
preprocessor
arithmetic
detail
array
comparison
config
control
detail
edg
msvc
detail
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iteration
detail
bounds
iter
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detail
edg
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tuple
regex
v3
test
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included
type_traits
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userfun.zip
ATL
release
UserFun.exe
LowLevel
release
LowLevel.exe
2000
release
2000.exe
whoami.zip
Whoami
release
Whoami.exe
//  (C) Copyright Gennadiy Rozental 2001-2002.
//  Permission to copy, use, modify, sell and distribute this software
//  is granted provided this copyright notice appears in all copies.
//  This software is provided "as is" without express or implied warranty,
//  and with no claim as to its suitability for any purpose.

//  See http://www.boost.org for most recent version including documentation.
//
//  File        : $RCSfile: floating_point_comparison.hpp,v $
//
//  Version     : $Id: floating_point_comparison.hpp,v 1.7 2002/11/02 19:31:04 rogeeff Exp $
//
//  Description : defines algoirthms for comparing 2 floating point values
// ***************************************************************************

#ifndef BOOST_FLOATING_POINT_COMPARISON_HPP
#define BOOST_FLOATING_POINT_COMPARISON_HPP

#include <boost/limits.hpp>  // for std::numareic_limits

#include <boost/test/detail/class_properties.hpp>

template<typename FPT>
inline FPT
fpt_abs( FPT arg ) 
{
    return arg < 0 ? -arg : arg;
}

//____________________________________________________________________________//

// both f1 and f2 are unsigned here
template<typename FPT>
inline FPT 
safe_fpt_division( FPT f1, FPT f2 )
{
    return  (f2 < 1 && f1 > f2 * std::numeric_limits<FPT>::max())   ? std::numeric_limits<FPT>::max() :
           ((f2 > 1 && f1 < f2 * std::numeric_limits<FPT>::min() || 
             f1 == 0)                                               ? 0                               :
                                                                      f1/f2 );
}

//____________________________________________________________________________//

template<typename FPT>
class close_at_tolerance {
public:
    explicit    close_at_tolerance( FPT tolerance, bool strong_or_weak = true ) 
    : p_tolerance( tolerance ), m_strong_or_weak( strong_or_weak ) {}

    explicit    close_at_tolerance( int number_of_rounding_errors, bool strong_or_weak = true ) 
    : p_tolerance( std::numeric_limits<FPT>::epsilon() * number_of_rounding_errors/2 ), 
      m_strong_or_weak( strong_or_weak ) {}

    bool        operator()( FPT left, FPT right ) const
    {
        FPT diff = fpt_abs( left - right );
        FPT d1   = safe_fpt_division( diff, fpt_abs( right ) );
        FPT d2   = safe_fpt_division( diff, fpt_abs( left ) );
        
        return m_strong_or_weak ? (d1 <= p_tolerance.get() && d2 <= p_tolerance.get()) 
                                : (d1 <= p_tolerance.get() || d2 <= p_tolerance.get());
    }

    // Data members
    BOOST_READONLY_PROPERTY( FPT, 0, () )
                p_tolerance;
private:
    bool        m_strong_or_weak;
};

//____________________________________________________________________________//

template<typename FPT, typename ToleranceSource>
bool
check_is_closed( FPT left, FPT right, ToleranceSource tolerance, bool strong_or_weak = true )
{
    close_at_tolerance<FPT> pred( tolerance, strong_or_weak );

    return pred( left, right );
}

//____________________________________________________________________________//

template<typename FPT, typename ToleranceSource>
FPT
compute_tolerance( ToleranceSource tolerance, FPT /* unfortunately we need to pass type information this way*/ )
{
    close_at_tolerance<FPT> pred( tolerance );

    return pred.p_tolerance.get();
}

//____________________________________________________________________________//

// ***************************************************************************
//  Revision History :
//  
//  $Log: floating_point_comparison.hpp,v $
//  Revision 1.7  2002/11/02 19:31:04  rogeeff
//  merged into the main trank
//

// ***************************************************************************

#endif // BOOST_FLOATING_POINT_COMAPARISON_HPP

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About the Author

oshah
Web Developer
United States United States
Mr. Shah is a reclusive C++/C# developer lurking somewhere in the depths of the city of London. He learnt physics at Kings' College London and obtained a Master in Science there. Having earned an MCAD, he teeters on the brink of transitioning from C++ to C#, unsure of which language to jump to. Fortunately, he also knows how to use .NET interop to merge code between the two languages (which means he won't have to make the choice anytime soon).
 
His interests (apart from programming) are walking, football (the real one!), philosophy, history, retro-gaming, strategy gaming, and any good game in general.
 
He maintains a website / blog / FAQ / junk at shexec32.serveftp.net, where he places the best answers he's written to the questions you've asked. If you can find him, maybe you can hire Mr. Shah to help you with anything C++[/CLI]/C#/.NET related Smile | :) .

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