Re: Sines and Cosines
On Sun, 23 Mar 2008 00:44:18 +0000, Kenneth P. Turvey wrote:
On Sat, 22 Mar 2008 08:58:59 -0400, Eric Sosman wrote:
O/S matters a lot, because the libraries are completely
different: You've got a Linux distribution with ...?... math
library, and I've got the DJGPP environment running atop
Windows. (An elderly DJGPP, too, as I pointed out.)
[Snip]
Ok, I found an example of the problem on the web in the initial report of
the problem as reported to Sun in Java. I implemented the first example
of the problem in C and, sure enough, my Intel box still displays the
problem. So my JVM is doing the right thing to work around the inaccuracy.
[Snip]
As a side note, here's the Java code from the original bug report. You
can be sure that this code will execute correctly on your computer. I'm
sure it is in the automated test suite at Sun. If, however, the C code I
provided returns the wrong answer, I would like to see this run, just to
make sure.
public class Test {
public static void main(String [] args) throws Exception {
//this is the output from JCK test:
//cos failed for 3ff921f0d7e968a9 Expected 3ee4f8b588dd0ce3 +/- 1 ulp Got: 3ee4f8b588dd0ce1
//cos failed for 3ff921fb54442d1b Expected bcc5cb3b399d747f +/- 1 ulp Got: bcc5cb4000000000
//sin failed for c01921fb54442d18 Expected 3cb1a62633145c07 +/- 1 ulp Got: 3cb1a60000000000
System.out.println("x1 = " + Double.longBitsToDouble(0x3ff921f0d7e968a9L));
System.out.println("x2 = " + Double.longBitsToDouble(0x3ff921fb54442d1bL));
System.out.println("cos(x1) = " + Math.cos(Double.longBitsToDouble(0x3ff921f0d7e968a9L)));
System.out.println("cos(x2) = " + Math.cos(Double.longBitsToDouble(0x3ff921fb54442d1bL)));
System.out.println("cos(x1) = " + StrictMath.cos(Double.longBitsToDouble(0x3ff921f0d7e968a9L)));
System.out.println("cos(x2) = " + StrictMath.cos(Double.longBitsToDouble(0x3ff921fb54442d1bL)));
System.out.println("x3 = " + Double.longBitsToDouble(0xc01921fb54442d18L));
System.out.println("sin(x3) = " + Math.sin(Double.longBitsToDouble(0xc01921fb54442d18L)));
System.out.println("sin(x3) = " + StrictMath.sin(Double.longBitsToDouble(0xc01921fb54442d18L)));
}
}
--
Kenneth P. Turvey <kt-usenet@squeakydolphin.com>