Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail
From: markspace <-@.>
Newsgroups: comp.lang.java.programmer
Subject: Re: higher precision doubles
Date: Sat, 06 Aug 2011 15:43:53 -0700
Organization: A noiseless patient Spider
Lines: 38
Message-ID: <j1kg3g$61c$1@dont-email.me>
References: <j1hqc1$1ch$1@news.albasani.net> <strictfp-20110806003831@ram.dialup.fu-berlin.de> <j1k4db$1n2$1@news.albasani.net> <j1k87t$kol$1@dont-email.me> <j1kb73$h3p$1@news.albasani.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Sat, 6 Aug 2011 22:44:00 +0000 (UTC)
Injection-Info: mx04.eternal-september.org; posting-host="XjIWM99mD7Ijfdu600oVPA"; logging-data="6188"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+bUUBf4XDri3nqQdRoJWlxE+uxt/6ybmQ="
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:5.0) Gecko/20110624 Thunderbird/5.0
In-Reply-To: <j1kb73$h3p$1@news.albasani.net>
Cancel-Lock: sha1:1+HU+j26Q1KrFWRFmX6XWUnJDpU=
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:6835

On 8/6/2011 2:20 PM, Jan Burse wrote:
> So if you add x == 0 to your solution, you would get:
>
>  > -0.000000, false
>  > -0.000000, false


"x == 0" is kind of a known rube-ism.  You can't compare floating point 
directly with any scalar, it just doesn't work.  You have to implement 
some sort of range check.  It is a bit of a bummer that Java doesn't 
provide such a method by default, but it's also not hard to implement.


public class FpPrint {

     public static void main( String[] args )
     {
         System.out.printf( "%6.6f\n", Math.sin( Math.PI * 2 ) );
         System.out.printf( "%6.6f\n", StrictMath.sin( StrictMath.PI * 2 
) );
         DoubleComparator c = new DoubleComparator( 0.000001 );
         System.out.println( c.compare(
                 StrictMath.sin( StrictMath.PI * 2 ), 0.0 ) );
     }
}

class DoubleComparator {
     private final double constraint;

     public DoubleComparator( double constraint )
     {
         this.constraint = constraint;
     }

     public boolean compare( double d1, double d2 ) {
         return Math.abs(d1-d2) < constraint;
     }
}