// filename:c2011-7-6-4-4-ex.c
// original examples and/or notes:
// 		(c) ISO/IEC JTC1 SC22 WG14 N1570, April 12, 2011
// 			C2011 7.6.4.4 The feupdateenv function
// compile and output mechanism:
// 		(c) Ogawa Kiyoshi, kaizen@gifu-u.ac.jp, December.29, 2013
// compile errors and/or wornings:
// 		(c) Apple LLVM version 4.2 (clang-425.0.27) (based on LLVM 3.2svn)
// 			Target: x86_64-apple-darwin11.4.2 //Thread model: posix
// 		(c) LLVM 2003-2009 University of Illinois at Urbana-Champaign.
#include <stdio.h>
// Example 
#include <fenv.h>
double f(double x)
{
#pragma STDC FENV_ACCESS ON
double result;
fenv_t save_env;
if (feholdexcept(&save_env))
return /* indication of an environmental problem */x;
result = x * x;
// compute result
if (/* test spurious underflow */1) // How can I test spurious underflow?
if (feclearexcept(FE_UNDERFLOW))
return /* indication of an environmental problem */x;
if (feupdateenv(&save_env))
return /* indication of an environmental problem */x;
return result;
}

int main(void)
{
double d=3.5;
return printf("7.6.4.4 The feupdateenv function %f \n",f(d));	
}
// output may be
// 7.6.4.4 The feupdateenv function 12.250000