Not to nitpick, but in your sample, you're better off using ++i instead of i++
in the interests of speed and memory.
________________________________
From: Alan Kent <alan.j.k...@saic.com>
To: javaposse@googlegroups.com
Sent: Wed, July 21, 2010 10:18:01 AM
Subject: [The Java Posse] Fastest way to parse data out of array of bytes?
I was wondering what the fastest way (most highly performant) was to parse data
structures serialized as an array of bytes. In my case its like a network
packet (a true array of bytes where I need to peel of 1, 2, 4, and 8 byte
integers, or variable length ASCII (8-bit) strings, etc.)
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.
Sample code that sneaks in:
byte b1 = buf[i++];
byte b2 = buf[i++];
byte b3 = buf[i++];
byte b4 = buf[i++];
int n = (b1 << 24) | ((b2 & 0xff) << 16) | ((b3 & 0xff) << 8) | (b4 &
0xff);
// Must mask with 0xff or else sign extension will mess up the result. Java
does
not have unsigned bytes or ints!
I was looking into array bounds checks, and what I found via Google indicated
that hotspot leaves in array bounds checks as there was only a minor
performance
improvement found in practice. This lead me to wonder if there is a faster way
to do the code since I would be doing lots of array accesses, each with a
bounds
check.
Just curious!
Thanks!
Alan
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