NO_SIGNALING_NAN.cpp

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// checking for signaling NaN
 
 
#include "config.h"
 
#include <stdio.h>
#include <float.h>
 
#if !defined (_RWSTD_NO_FENV_H)
   // [try to] get floating-point exception support
#  include <fenv.h>
#else
#  include <ieeefp.h>
#endif   // _RWSTD_NO_FENV_H
 
 
#ifndef _RWSTD_NO_INFINITY
 
#  if defined _RWSTD_DBL_SNAN_BITS
 
union {
    char bits[sizeof (double)];
    double val;
} snan = { _RWSTD_DBL_SNAN_BITS };
 
// assignment or initialization should not trap
static double d = snan.val;
 
#  else   // if !defined (_RWSTD_DBL_SNAN_BITS)
 
double foo ()
{
    const int endian = 1;
 
    // compute infinity (division may trap)
    double x = 0.0;
    x = 1.0 / x;
 
    // turn infinity into a signaling NaN by setting the LSB
    ((char*)&x)[(sizeof x - 1) * (!!*(char*)&endian)] |= 1;
 
    return x;
}
 
static double d = foo ();
 
#  endif   // _RWSTD_DBL_SNAN_BITS
 
 
#endif   // _RWSTD_NO_INFINITY
 
 
// prevent optimizers from eliminating expressions such as (d == d)
volatile double *pd = &d;
 
 
int main ()
{
    // floating point operations on SNAN's might trap
    // if that happens the test will be considered successful
 
#if    defined (FE_DIVBYZERO) || defined (FE_INEXACT) || defined (FE_INVALID) \
    || defined (FE_OVERFLOW)  || defined (FE_UNDERFLOW)
 
#  pragma STDC FENV_ACCESS ON
 
    const int all = 0
 
#  ifdef FE_ALL_EXCEPT
        | FE_ALL_EXCEPT |
#  else   // if !defined (FE_ALL_EXCEPT)
 
#    ifdef FE_DIVBYZERO
        | FE_DIVBYZERO |
#    endif   // FE_DIVBYZERO
 
#    ifdef FE_INEXACT
        | FE_INEXACT |
#    endif   // FE_INEXACT
 
#    ifdef FE_INVALID
        | FE_INVALID |
#    endif   // FE_INVALID
 
#    ifdef FE_OVERFLOW
        | FE_OVERFLOW |
#    endif   // FE_OVERFLOW
 
#    ifdef FE_UNDERFLOW
        | FE_UNDERFLOW |
#    endif   // FE_UNDERFLOW
 
#  endif   // FE_ALL_EXCEPT
 
        0;   // defintion of all
 
 
    // assume a C99 conforming environment
    feclearexcept (all);
 
    d *= d;
 
    if (fetestexcept (all))
        return *pd != d;   // have a SNAN
 
    d /= d;
    
    if (fetestexcept (all))
        return *pd != d;   // have a SNAN
 
#elif defined (sun) || defined (__sun) || defined (__sun__)
 
    fpsetsticky (0);
 
    // any math operation should trap
    d *= d;
 
    if (fpgetsticky ())
        return *pd != d;   // have a SNAN
 
    d /= d;
    
    if (fpgetsticky ())
        return *pd != d;   // have a SNAN
 
#endif   // sun
 
    // NEGATIVE test: successful exit status indicates a failure
    return 0;
}