public int bitLength ()

Returns the number of bits in the minimal two's-complement
representation of this BigInteger, *excluding* a sign bit.
For positive BigIntegers, this is equivalent to the number of bits in
the ordinary binary representation. (Computes
` (ceil(log2(this < 0 ? -this : this+1)))`

.)

*excluding* a sign bit.

Diagram: BigInteger, BigDecimal