Re: Looking for Long Tooth...

[Henri Yandell <bayard@generationjava.com>]

Yeah. This seems to be a major 'plus' to bitwise manipulation. Improved
performance given a diminishing readability.

For example, rather than using a boolean[], we could be using a BitMask
class or an int [depending on size of array etc].

The biggest problem here is that for many developers, the only need to
learn and get used to the bitwise syntax would be to understand the
performance enhancements. A bit of a catch-22.

As with most optimisation, it fits into the category of doing it after
you've deduced you have a problem. With lots of nice comments.

Hen

On 9 Apr 2003, Christopher Fowler wrote:

> Another point is that everytime you use a boolean in Java, you could
> store that same info in 1 bit.
>
>
> On Wed, 2003-04-09 at 09:39, Henri Yandell wrote:
> >
> >
> > On Wed, 9 Apr 2003, Scott P. Smith wrote:
> >
> > > I am a little surprised by this question and the other one like it a few
> > > weeks ago.  I have a sneaky feeling that I am helping a college student do
> > > his homework, but I'll respond anyway.
> >
> > I don't find it as surprising. Most of the bitwise manipulation I've come
> > into direct contact with has not been very necessary, but just a result of
> > old C habits being transferred to the language in question. Irritating
> > things like:
> >
> >  i ^= i;   or somesuch.
> >
> > Many Java developers out there have not spent time working in C, and in
> > many other languages there's not the need for the low-level bitwise stuff.
> >
> > > There are infinitely many ways these operators can be useful.. But I'll just
> > > give a few examples:
> >
> > Major ones I've come into contact with are encryption algorithms and
> > encoding algorithms. At work we encode a series of numbers into one long
> > for transmission. I've found BigInteger to have surprising powers here at
> > extracting the values. [for when our long got larger than a java long]
> >
> > Having a look at the source to an encryption algorithm will see some very
> > important uses of bit-shifting.
> >
> > > * Data Compression - Many data compression algorithms compress byte streams
> > > into bit streams.  To create (and later decode) the bit streams, you need
> > > bitwise operators.
> > >
> > > * Non-Java Binary File I/O - When working with binary files that were
> > > created in C, C++, etc. you will see a lot of use of things like unsigned
> > > 16, and 32 bit values. Since Java doesn't support these, you have to use
> > > bitwise operators to put the uint16 into a Java int32. And vise versa.
> >
> > Apache's POI project is probably a good example of this. It reads MS
> > Office formats and as far as I know is full of a need to bit-shift. Having
> > a look at their source is probably an education.
> >
> > > * Arbitrarily Precision Integer Math - Math packages that implement 64, 128,
> > > 256 bit integers, etc.  These packages use bitwise operators (at least I
> > > think they do).
> >
> > BigInteger :)
> >
> >
> > Hen
>
>