In the documentation to 'BigDecimal#power', the optional `prec' argument 
is not even mentioned.
You can reduce the number of significant digits by class method limit

 b=BigDecimal.new("1.034482758620689655172413793103448275862068965517241379310344827586206896551724")
BigDecimal::limit(5)
b.power(4, 123456789)    # "1.1453", prec argument is ignored

It seems there is a bug in this method implementation. Too busy to 
investigate myself.

Would you fill a bug report on ruby-lang.org ?

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