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From: Jan Burse <janburse@fastmail.fm>
Newsgroups: comp.lang.java.programmer
Subject: BitSet vs BigInteger (false Android doc)
Date: Fri, 02 Sep 2011 21:48:06 +0200
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Dear All,

Just notice the following note on Android for
java.lang.BigInteger:

      Slow Two's Complement Bitwise Operations
	This API includes operations for bitwise operations
	in two's complement representation. Two's complement
	is not the internal representation used by this
	implementation, so such methods may be inefficient.
	Use BitSet for high-performance bitwise operations
	on arbitrarily-large sequences of bits.

But why should be BitSet any faster than BigInteger? Both
BitSet and BigInteger don't use some sparse representation.
They just allocate an array, in the case of BitSet its a long
array, and in the case of BigInteger int array.

The BigInteger sign does not slow down the process in any way.
Its just that the highest int of the BigInteger carries a sign,
which is arbirarily extended to the left. So BigInteger can
represent:

      ....1xxxxxx

With an infinite sequence of 1's to the left. And then do
boolean operation. But there is practically no overhead
for that. But what I saw is that BitSet is not immutable,
so this could be a reason. But the two's complement is
not an issue, this is just rubbish.

Right?

Bye