Overloading C++ operator<< to accept an __int128 from GCC/Clang

int128.cc

/**
 * @file
 */

#include "int128.h"

/*
 * http://stackoverflow.com/a/25115163
 */
std::ostream& operator<<(std::ostream& os, const __int128 i) noexcept
{
  std::ostream::sentry s(os);
  if (s) {
    unsigned __int128 tmp = i < 0 ? -i : i;
    char buffer[128];
    char *d = std::end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (i < 0) {
      --d;
      *d = '-';
    }
    int len = std::end(buffer) - d;
    if (os.rdbuf()->sputn(d, len) != len) {
      os.setstate(std::ios_base::badbit);
    }
  }
  return os;
}

int128.h

/**
 * @file
 *
 * Support for 128-bit integers in GCC and Clang.
 */

#ifndef __INT128_H__
#define __INT128_H__

 /*
  * Standard
  */
#include <iostream>

/**
 * Overload the ostream operator << to support 128-bit integers.
 */
std::ostream&
operator<<( std::ostream& dest, const __int128 value )
noexcept;

#endif /* __INT128_H__ */

int128test.cc

/**
 * @file
 */

/*
 * Catch
 */
#include <catch.hpp>

#include "int128.h"

TEST_CASE( "std::ostream::operator<<", "[int128]" ) {
  __int128 INTEGERS[] = {0, -1, 1, 1234567890};
  std::string STRINGS[] = {"0", "-1", "1", "1234567890"};
  for (size_t i = 0; i < sizeof(INTEGERS)/sizeof(INTEGERS[0]); i++) {
    std::stringstream ss;
    ss << INTEGERS[i];
    CHECK(ss.str() == STRINGS[i]);
  }
}

TEST_CASE( "<=>", "[int128]" ) {
  __int128 a = 5;
  __int128 b = 7;
  bool test1 = (a < b);
  bool test2 = (b > a);
  REQUIRE(test1);
  REQUIRE(test2);
}