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Re: Compiling IDL ... ever likey ? [message #5699 is a reply to message #5518] Tue, 23 January 1996 00:00 Go to previous messageGo to previous message
Rick White is currently offline  Rick White
Messages: 2
Registered: January 1996
Junior Member
Ken Knighton wrote:

> Languages that compile to the host machine level are rapidly becoming
> obsolete and investing programming time into turning a very efficient
> pseudo-compiled, array oriented language like IDL into a true compiled
> language is a waste of resources that could be better used to improve
> other features of IDL. For example: I haven't heard anyone suggesting
> that JAVA be turned into a compiled language.

You're wrong -- there are definitely plans to produce Java compilers
that turn Java binaries into native machine code. These compilers
are seen by the Java community as crucial to getting good performance
on computationally intensive applications.

I think the Java approach could serve as a good model for an IDL
compiler. Java gets compiled to an intermediate, machine independent
pseudo-code which is (ordinarily) executed by the Java interpreter.
The execution penalty of the interpreted code compared with C is
about a factor of 20. The new compilers will replace the
interpreter and will translate the Java pseudo-code into native machine
instructions at execution time. This on-the-fly (or "just-in-time")
compilation will produce code that executes at nearly the same speed
as C (I haven't seen any hard numbers.)

I think this approach could work very well for IDL. Most IDL code
executes efficiently enough in interpreted mode, especially when you're
doing large array operations where each step takes a considerable
amount of compute time. The slowdown comes if some part of
your calculation can't be done as an array operation but must be
written as an explicit loop over array elements. Then IDL is, like
Java, a factor of 20 (or more) slower than C (so it's not just a matter
of a few cycles here and there.) If such loops could be compiled
on-the-fly then IDL's speed would be comparable to C/Fortran for
essentially all applications.

Perhaps someone should be working on an IDL-to-Java translator or even
an IDL-to-Java pseudo-code compiler!

--
Richard L. White rlw@stsci.edu http://sundog.stsci.edu/rick/
Space Telescope Science Institute
Baltimore, MD

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