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Re: floating-point efficiency: Lisp vs. Fortran (FYI)
- To: firstname.lastname@example.org, hmadorf <@brazil.cambridge.apple.com:email@example.com>
- Subject: Re: floating-point efficiency: Lisp vs. Fortran (FYI)
- From: Jeff Dalton <firstname.lastname@example.org>
- Date: Wed, 14 Oct 92 15:36:12 BST
> Two versions of the CL code were tested, one without declarations,
> the other fully spiced with declarations. The CL-code was compiled
> with (speed 3) optimization. The Fortran code was not particularly
> optimized. My observations:
> 1. Declarations had little influence on CL-execution efficiency.
I have seen a large effect in some cases such as, say, summing
or scaling rows and columns of a matrix. Some possibilities:
* The CL you're using doesn't optimize floating point very well.
* It optimizes floating point fairly well even without declarations
so that declarations don't make a big difference.
* Some potential optimizations aren't performed because of the
way you wrote your code. (Eg, perhaps you didn't specify
result types using something like (THE DOUBLE-FLOAT ...).)
* Your code does things that can't (easily?) be optimized.
(For instance, it's hard for an implementation to avoid
heap-allocating floats when passing them to a global procedure.)
* You're using a non-primitive floating point operation that
isn't implemented very well. (For instance, I wouldn't be
surprised if the log function was inefficiently implemented
in several Common Lisps.)
* You're doing some other thing, in addition to fp operations,