fuzztest.C

#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>
#include <cstdlib>
#include <cmath>

typedef double Real;

int main()
{
  unsigned int nans = 0;
  Real in;
  Real out;

  for (unsigned n = 0; n < 10000000; ++n)
  {
    const unsigned int num_bytes = sizeof(Real);
    for (unsigned int i = 0; i < num_bytes; ++i)
      reinterpret_cast<unsigned char *>(&in)[i] = std::rand() & 255;

    if (std::isnan(in))
    {
      nans++;
      continue;
    }

    std::stringstream si;
    si << std::scientific
       << std::setprecision(std::numeric_limits<Real>::digits10 + 1)
       << in;

    std::stringstream so(si.str());
    so >> out;

    if (out != in)
    {
      std::cout << "Lost precision!" << in << " - " << out << " = " << (in-out) << '\n';
      return 1;
    }
  }

  std::cout << "Precision fully retained! (" << nans << " nans)\n";
  return 0;
}