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BitSet vs boolean[]

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  BitSet vs boolean[] Roedy Green <see_website@mindprod.com.invalid> - 2014-07-18 11:51 -0700
    Re: BitSet vs boolean[] Robert Klemme <shortcutter@googlemail.com> - 2014-07-18 21:11 +0200

#29118 — BitSet vs boolean[]

In terms of minimising space, how big must a boolean array be before
it pays to use a BitSet?
-- 
Roedy Green Canadian Mind Products http://mindprod.com
Science is what we understand well enough to explain to a computer.
Art is everything else we do. 
~ Donald Ervin Knuth (born: 1938-01-10 age: 76)

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#29119

On 18.07.2014 20:51, Roedy Green wrote:
> In terms of minimising space, how big must a boolean array be before
> it pays to use a BitSet?

Well, a BitSet has these members
- long[]
- int
- boolean

If I'm not mistaken that yields sizeof(ref) + 8 * length + 4 + 4 = 
sizeof(ref) + 8 * (length + 1) bytes with length > 0 so at least 
sizeof(ref) + 16 bytes.  I'd say worst case this is 8 + 16 = 24 bytes. 
Sinze a BitSet grows dramatically slower (on average 8 times) than a 
byte array if you add items that should be the max size.

Of course, you can save even more memory by using a byte, short, int or 
long if you know the max set size is 8, 16, 32 or 64 bits and implement 
all the operations via bit logic.

Kind regards

	robert

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