Re: finding primes


Chris Uppal wrote:
Azumanga wrote:


On the other hand, we are assuming that sqrt(n*n) results in
exactly n and not:
(n-1)+0.9999999999999999

In any language I'm familar with, if you found an n where that
happened, you'd submit a HUGE bug comment to the people who make the
langauge.

Will Java do ?

=====================
import java.math.BigInteger;

public class Test
{
public static void
main(String[] args)
{
// NB: n is representable as <= 64 bits, it is actually
// (1L << 60) + 1
BigInteger n = new BigInteger("1152921504606846977");
BigInteger squared = n.multiply(n);

// have to convert to double to get the square root
double root = Math.sqrt(squared.doubleValue());

// and...
System.out.println(n);
System.out.println((long)root);
}
}
=====================

Or any other language which can handle big integers but which doesn't
naturally represent floating point in arbitrary-precision.


If you are going to start casting to doubles, then all your problems
are your own :)

Chris

.

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