Re: [Caml-list] Bigarray is a pig

[Brian Hurt <bhurt@spnz.org>]

On Fri, 23 Jul 2004, Brandon J. Van Every wrote:

> I have been looking at the sources of the Bigarray implementation.  I am
> chagrined to discover that not only does Bigarray cost a function call
> per array element access, but a number of additional piggish things
> happen per access.  

If memory serves, Ocaml can optimize the access if the size and type are 
known, getting rid of the function call overhead and type specialization.  
I don't think it gets rid of the bounds checking, tho- which is good.

Can someone who actually knows what is going on clarify this?

> To C/C++ programmers interested in performance, this
> defeats the purpose of using unboxed array elements.  If I wanted to pay
> function call overhead per element, for instance when communicating with
> OpenGL, I'd simply call functions.

Function calls aren't that expensive.  From comments in other forums:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=cdjsuj%24cs6%241%40wolfberry.srv.cs.cmu.edu

may I respectfully suggest that you are prematurely optimizing?  A 
function call to a known function takes 1-2 clock cycles.  A cache miss, 
on the other hand, can take hundreds of clock cycles:
http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&threadm=45022fc8.0407221624.6fd81ad0%40posting.google.com&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUTF-8%26group%3Dcomp.arch


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Brian

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