Ah yes, the difference between being rational and precise :-D
In programming fortran for IBM 370s you couldn't say:
IF ( A.EQ.1.0 )
You had to say something like:
IF ( ABS(A-1.0).LT.EPSILON )
where EPSILON = 0.0001
REALly
My Finance Professor Father who compiled the first statistically
reliable database of NYSE stock prices (Monthly 1925 - 1964 - the
CRSP monthly database still maintained by the GSB at the University
of Chicago ) has always remarked about the trouble he had when he had
to convert to the IBM 360 in the early 60's. A REAL number went from
being in a Word of 6 bytes of 6 bits to Words of 4 bytes of 8 bits.
His dataset had to be converted from SINGLE to DOUBLE because the
loss of precision of going from 36 bits to 32 bits adversely effected
his results.
A good computer scientist must know how precise their calculations
are and make the trade offs.
Takahiro is encountering the fact that different implementations have
made their own decisions about numeric representations and it can be
hard to know how POI's are different from Open Office or Microsoft's.
For information on floating point: http://en.wikipedia.org/wiki/
IEEE_754 and follow some of the external links.
Regards,
Dave
On Mar 1, 2007, at 11:37 AM, Andrew C. Oliver wrote:
You do realize that floating point numbers are always
approximates? Both of the numbers below
are "correct" ;-)
Are you sure this is not a bug of POI? This is not a random
problem. It
always does so for the file. Also I can't enforce the decimal
places. Also when I save as CSV and then back to XLS, this doesn't
happen.
I debugged a little and figure out that the LittleEndian.getDouble
(final
byte[] data, final int offset) method returns different long bits
value
(one last digit is different), 4562254508917369340 (Corrent) and
4605101755772172238 (Wrong), which is pass to the Double to get the
double value.
I have attached the sample file so that the problem can be
reproduced. This file is created with the open office 2 by copying
paste cells from
the problematic ms excel xp file.
Takahiro
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