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ImfRational.cpp

///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2006, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// *       Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// *       Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// *       Neither the name of Industrial Light & Magic nor the names of
// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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///////////////////////////////////////////////////////////////////////////

//-----------------------------------------------------------------------------
//
//    Rational numbers
//
//    The double-to-Rational conversion code below
//    was contributed to OpenEXR by Greg Ward.
//
//-----------------------------------------------------------------------------

#include <ImfRational.h>
#include <cmath>

using namespace std;

namespace Imf {
namespace {

double
frac (double x, double e)
{
    return x - floor (x + e);
}


double
square (double x)
{
    return x * x;
}


double
denom (double x, double e)
{
    if (e > frac (x, e))
    {
        return 1;
    }
    else
    {
      double r = frac (1 / x, e);
      
        if (e > r)
        {
            return floor (1 / x + e);
        }
        else
        {
            return denom (frac (1 / r, e), e / square (x * r)) +
                   floor (1 / x + e) * denom (frac (1 / x, e), e / square (x));
        }
    }
}

} // namespace


Rational::Rational (double x)
{
    int sign;

    if (x >= 0)
    {
      sign = 1;   // positive
    }
    else if (x < 0)
    {
      sign = -1;  // negative
      x = -x;
    }
    else
    {
      n = 0;            // NaN
      d = 0;
      return;
    }

    if (x >= (1U << 31) - 0.5)
    {
      n = sign;   // infinity
      d = 0;
      return;
    }

    double e = (x < 1? 1: x) / (1U << 30);
    d = (unsigned int) denom (x, e);
    n = sign * (int) floor (x * d + 0.5);
}


} // namespace Imf

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