Is there something about log(0.5) which is a mathematical singularity? 
use bugnum;
say log(0.5);

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Gives: Can't locate object method "_log" via package "Math::BigInt" at /home/jima/perl5/lib/perl5/Math/BigFloat.pm line 5737.

Any other value works, such as 

say log(0.5000000000000000000000000000000000000000000001);
say log(0.4999999999999999999999999999999999999999999999);

[download]
(which both print '-0.6931471805599453094172321214581765680755')

In reply to log(0.5) with bignum blows up by jimav

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