/ray/src/lib/numerics/macheps.cc

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/*
 * lib/numerics/macheps.cc
 * 
 * Compute machine precision for numerics code. 
 * 
 * Copyright (c) 2003--2004 by Wolfgang Wieser ] wwieser (a) gmx <*> de [ 
 * 
 * This file may be distributed and/or modified under the terms of the 
 * GNU General Public License version 2 as published by the Free Software 
 * Foundation. (See COPYING.GPL for details.)
 * 
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 * 
 */

#include "num_math.h"


namespace NUM
{

template<typename T>static volatile void _CME_add1(T x,volatile T *res);

template<typename T>static volatile T _ComputeMachEps1()
{
    volatile T e=1.0e-5,pe=e,e1;
    do {
        pe=e;
        e/=1.5;
        _CME_add1(e,&e1);
    } while(e1>1.0);
    //fprintf(stderr,"Computed macheps1=%g=pow(2,%.2f) (sizeof(T)=%u)\n",
    //  pe,log(pe)/log(2.0),sizeof(T));
    return(pe);
}

template<typename T>static volatile void _CME_add1(T x,volatile T *res)
{
    *res=1.0+x;
}

// This computes the precision macheps...
template<typename T>static T _ComputeMachEps1_Prec()
{
    register T e=1.0e-5,pe=e;
    while(1.0+e>1.0)
    {  pe=e;  e/=1.5;  }
    //fprintf(stderr,"Computed macheps1_prec=%g\n",pe);
    return(pe);
}


// Initialize global data: 
const FPConst<dbl> fpconst_dbl=
{
    INIT_FIELD(macheps1) _ComputeMachEps1<dbl>(),
    INIT_FIELD(sqrt_macheps1) sqrt(_ComputeMachEps1<dbl>()),
    INIT_FIELD(macheps1_prec) _ComputeMachEps1_Prec<dbl>()
};

const FPConst<flt> fpconst_flt=
{
    INIT_FIELD(macheps1) _ComputeMachEps1<flt>(),
    INIT_FIELD(sqrt_macheps1) sqrt(_ComputeMachEps1<flt>()),
    INIT_FIELD(macheps1_prec) _ComputeMachEps1_Prec<flt>()
};

}  // end of namespace NUM

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