Vim & Vision
[ #47 ] bignum to the Rescue Permalink
Normal use of Perl suffers from the same floating point numerical errors as many other languages:
$ perl -e '$a = .1; $b = .3/3; print "OK\n" if ($a == $b)'
$
If you use the bignum library however, this error disappears:
$ perl -Mbignum -e '$a = .1; $b = .3/3; print "OK\n" if ($a == $b)'
OK
$
R suffers from the problem too:
> .1
[1] 0.1
> .3/3
[1] 0.1
> (.1 == .3/3)
[1] FALSE
... and it's because:
$ perldoc -q "long dec"|perl -ne '$x=1 if /Inte/; $x=0 if /^$/; $x && print'
Internally, your computer represents floating-point numbers in binary.
Digital (as in powers of two) computers cannot store all numbers
exactly. Some real numbers lose precision in the process. This is a
problem with how computers store numbers and affects all computer lan-
guages, not just Perl.
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