I have encountered a rounding problem when sending floating-point numbers
from perl to java using Inline::Java. This is on CentOS 4 on an Intel
pentium 4 with jdk 1.3.10 and perl 5.6.2. We have a math library with dual
implementations; one in perl and one in java, and we have been seeing
sporadic differences. I have tracked the problem down to this: if I take a
number like 0.056200000000000028 in perl and then send it to java using
Inline::Java, java just gets 0.0562, which leads to small differences. I
confirmed that unpack "U*", $x yields the same values (48, 46, 48, 53, 54,
50) for $x = 0.0562 as well as $x = 0.056200000000000028, indicating that,
at least to perl, there is no difference between these numbers. However, if
$x = "0.056200000000000028", I get 48, 46, 48, 53, 54, 50, 48, 48, 48, 48,
48, 48, 48, 48, 48, 48, 48, 48, 48, 50, 56, as you might expect. If I hack
Inline::Java::Class::CastArgument to sprintf("%0.18f", $arg) when $proto is
'double', the differences between the perl library and the java library go
away. I find this somewhat confusing, because I would have thought that on
the same machine, perl's (c's) representation of a floating point number and
java's would have agreed. Can anyone shed some light on what is going on
here, and also what the most appropriate remedy might be?
Thanks,
Benjamin Holzman
