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Bogdan Pistol updated DIRMINA751:

Attachment: patchlookuptables.txt
IoBufferTest.java
Ok, I've written the JUnit test (it's attached to this issue), but I also had another idea
to make this even faster
the new implementation is 60% faster.
I'll stop here with the improvements for normalizeCapacity() :), I think it's enough.
> IoBuffer.normalizeCapacity improvement
> 
>
> Key: DIRMINA751
> URL: https://issues.apache.org/jira/browse/DIRMINA751
> Project: MINA
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0.0RC1
> Environment: N/A
> Reporter: Bogdan Pistol
> Priority: Minor
> Fix For: 2.0.0RC2
>
> Attachments: IoBufferTest.java, IoBufferTest.java, IoBufferTest.java, patchlookuptables.txt,
patch.txt
>
>
> The technique of computing the minimum power of 2 that is bigger than the requestedCapacity
in the org.apache.mina.core.buffer.IoBuffer.normalizeCapacity() is not optimal.
> The current computation is as follows:
> int newCapacity = 1;
> while ( newCapacity < requestedCapacity ) {
> newCapacity <<= 1;
> if ( newCapacity < 0 ) {
> return Integer.MAX_VALUE;
> }
> }
> The time complexity of this is O(n), where n is the number of bits of the requestedCapacity
integer, that is log2(requestedCapacity)  maximum 31.
> This creates an unnecessary overhead in some high IoBuffer allocations scenarios that
are calling IoBuffer.normalizeCapacity() a lot when creating IoBuffers. I observed this when
benchmarking a MINA server with hprof.
> There is a better solution to this problem than to iterate the bits from 0 to log2(requestedCapacity).
> The alternative is to use a binary search technique that has optimal time complexity
of O(5). Because requestedCapacity is an integer and has a maximum of 2^5 (32) bits we can
binary search in the set of bits and determine in O(5) comparisons the minimum power of 2
that is bigger than the requestedCapacity.

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