I don't think this is a bug, just an artifact of the transition between IEEE float constants and bignum objects: 

c:\>perl -MMath::BigFloat 
-wle"print Math::BigFloat->new(1) - Math::BigFloat->new( .999999999999
+999 )"
0.000000000000001

c:\>perl -MMath::BigFloat 
-wle"print Math::BigFloat->new(1) - Math::BigFloat->new( .999999999999
+9999 )"
0

c:\>perl -MMath::BigFloat 
-wle"print Math::BigFloat->new(1) - Math::BigFloat->new('.999999999999
+9999')"
0.0000000000000001

c:\>perl -MMath::BigFloat 
-wle"print Math::BigFloat->new(1) - Math::BigFloat->new('.999999999999
+99999999999')"
0.00000000000000000000001

[download]

Notice how once you get beyond ~16 decimal places in the constant, the result is wrong. However, if you pass the constant as a string rather than allowing Perl to convert it to a IEEE float before passing it to bignum, the accuracy is retained.

So the answer is to use string constants to initialise your bignum objects.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: Help me make a test case for Math::BigFloat by BrowserUk
in thread Help me make a test case for Math::BigFloat by fizbin

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