RFR: 8231717: Improve performance of EBCDIC charset decoding for COMPACT_STRINGS

[Andrew Leonard]

Hi,
Please can I request a review of this performance enhancement for EBCDIC 
(and any SingleByte, always compactable) charsets? I've explained the 
theory in the bug (https://bugs.openjdk.java.net/browse/JDK-8231717), but 
essentially it optimizes any SingleByte charset that is always compactable 
due to all mappings being to <=0xff and avoids unnecessary char[] to 
internal Latin1 byte[] arraycopy as a result. This leads to up to a 100% 
performance gain for decoding these charsets.
I have run the complete tier1 and also the complete sun/nio/cs testcases 
successfully.

Webrev: http://cr.openjdk.java.net/~aleonard/8231717/webrev.00/

Thoughts and comments welcome please?
Thanks
Andrew

Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
internet email: andrew_m_leonard at uk.ibm.com 

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