BigDecimal.doubleValue() is depressingly slow

A DESCRIPTION OF THE PROBLEM :
I find the following slow path in BigDecimal:

        // Somewhat inefficient, but guaranteed to work.
        return Double.parseDouble(this.toString())

Since JDK-7131192 : BigInteger.doubleValue() is depressingly slow
is now available, something faster could be done.

It suggest doing unscaledValue().doubleValue() * Math.exp(scale()*Math.log(10))