Peculiar fruits in the JDK

[Martin Buchholz]

Optimizing the decoder lookup tables is equivalent to
the C switch statement optimization problem.

Determined humans are likely to do better than javac at producing bytecode
that will JIT well because
- javac is not designed to be an optimizing compiler.
  javac will generate complicated code that the hotspot optimizer
  may have a hard time with.
- humans have special knowledge about the frequency of particular characters.
  E.g. they may know that the euro character is relatively rare.

I've considered (but not seriously) writing a special compiler
that takes as input the conversion tables and the empirical
frequency of characters in text in various encodings
and outputs a combination of table lookups and nested ifs that
will perform very well in practice.

Martin

On Tue, Jun 24, 2008 at 9:15 AM, David M. Lloyd <david.lloyd at redhat.com> wrote:
> On 06/24/2008 11:08 AM, Ulf Zibis wrote:
>>
>> I many cases I also could shorten the encoding mappings.
>>
>> Example:
>> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/branches/milestone1/src/sun/nio/cs/ext/IBM870.java?rev=223&view=markup
>
> Would a 'switch' statement not be more speed- and space-efficient for this
> type of lookup task?
>
> - DML
>