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Subject: [boost] [Random] Question on random_test.cpp
From: n1driver_at_[hidden]
Date: 2009-03-27 13:59:08

The following is an excerpt from the random_test.cpp file (part of the
instantiate_urng function):
 urng2 = urng;
    // narrow stream first
    std::ostringstream file;
    file << urng;
    // move forward
    // restore old state
    std::istringstream input(file.str());
    input >> urng;
    // std::cout << file.str() << std::endl;
#if !defined(BOOST_MSVC) || BOOST_MSVC > 1300 // MSVC brokenness
    // advance some more so that state is exercised
    for(int i = 0; i < 10000; ++i) {
    BOOST_CHECK(urng == urng2);
#endif // BOOST_MSVC
My concern is that when a random number generator with an underlying double type (like fibonacci607) is stored to the stream and then pulled back out, then
precision may be lost, and the underlying data is not guaranteed to be the same.
If a double is written out to a stream in decimal form and then read back in the
value may be changed. Am I missing some sort of language guarantee that this is
supposed to work? I've tried this on AIX and the test failed at this point for
fibonacci607 because some (but not all) of the underlying doubles had changed
after the object was stored and retrieved.

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