If you care about speed put together a good set of performance tests
to measure what you're doing.
On the specific example you could avoid some of the intermediate
variables and a few implicit widening operations (however hotspot will
probably optimise this for you). Probably drop it into a static
method for a bit of reuse:
public static int toInt(byte[] buf, int offset) {
return (buf[offset] & 0xFF) << 24 + (buf[offset + 1] & 0xFF) <<
16 +
(buf[offset + 2] & 0xFF) << 8 + (buf[offset + 3] &
0xFF);
}
There are a whole bunch of these methods in java.io.Bits (package
protected) which may help with your implementation.
Mike.
On Jul 21, 8:38 pm, Fabrizio Giudici <[email protected]>
wrote:
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>
> > Note I am after the FASTEST way to do this in Java (and/or Scala).
> > Is it better to use the stream based classes, or is it better to
> > do direct array accesses and do bit shift operations and masks
> > with 0xff etc (to strip sign extension Java will do otherwise)? I
> > suspect the stream based approaches would be slower.
>
> I think you have to try and measure. I've faced the same problem with
> image decoding. The ImageI/O API contains an ImageInputStream which is
> supposed to have some optimizations - even for bitwise, not only
> bytewise operations. When I first worked on it a few years ago, I
> found that writing some specific classes for specific cases (e.g.
> reading 12 or 16 bits) was faster - in other words, the library didn't
> provide the faster code. A few time later, I discovered that some
> newer JRE was better and dropped some of my code because it was
> useless. So, it's a matter of trying, measuring and re-measuring for
> each JRE update.
>
> - --
> Fabrizio Giudici - Java Architect, Project Manager
> Tidalwave s.a.s. - "We make Java work. Everywhere."
> java.net/blog/fabriziogiudici -www.tidalwave.it/people
> [email protected]
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