test uint52_t

255-test.cpp

#include <iostream>
#include <cinttypes>

using namespace std;

void display(double d)
{
  const uint64_t u = *reinterpret_cast<uint64_t*>(&d);

  const auto sign = u >> 63;
  const auto exponent = (u >> 52) & ((1 << 11) - 1);
  const auto fraction = u & ((static_cast<uint64_t>(1) << 52) - 1);

  cout << d << endl;
  cout << "\tsign: " << sign << endl;
  cout << "\texponent: " << exponent << endl;
  cout << "\tfraction: " << fraction << endl;
}

double convert(uint64_t sign, uint64_t exponent, uint64_t fraction)
{
  uint64_t u = (sign << 63) + (exponent << 52) + fraction;
  return *reinterpret_cast<double*>(&u);
}

double count_niters(uint64_t n)
{
  const auto x = convert(0,0,n);
  const auto one = convert(0,0,1);
  auto counter = convert(0,0,0);

  for (double x1 = 0, x2 = convert(0,0,70); x1 != x2; ) {
    display(x2);
    x1 = x2;
    const auto u1 = x1/one;
    x2 = (x1 + (x + x1 - one) / u1) / 2;
    counter += one;
  }

  return counter;
}

int main(void)
{
  display(count_niters(4321));
}

/*
 * $ ./a.out
 * 3.45846e-322
 * 	sign: 0
 * 	exponent: 0
 * 	fraction: 70
 * 3.26083e-322
 * 	sign: 0
 * 	exponent: 0
 * 	fraction: 66
 * 9.88131e-324
 * 	sign: 0
 * 	exponent: 0
 * 	fraction: 2
 */