Re: My second attempt at a data_xfer instruction optimization

	Your comment would be only valid for the functions where 
write_virtual_whatever is called and has no effect where 
read_virtual_whatever is called. It also assumes that the compiler is 
capable of making this type of optimization. In my experience it is 
never a good idea to rely on the compiler to do your dirty work because 
often it won't. Desired behaviour of code should be explicitly defined 
when possible.

	Your comment about vunerability to bugs in write_virtual_whatever is 
valid, unfortunaly writing code that is resilient to bugs is often slow. 
Slow is not something we want in code that is emulating an instruction 
that is one of the most frequently called. In my experience writing code 
to be tollerant of bugs is a double edged sword. It makes a piece of 
code less suceptable to a bug but does nothing to correct the problem ( 
The bug itself ). It also may make a bug harder to find and diagnose.

	My programing techniques may run afowl of common CS pratices but I base 
these on my experience in the real world with embedded programming.


Brian Slechta wrote:
> Hi,
>
> I am assuming that the reason the compiler could not safely remove these 
> temporary variables is because the "data" parameter in write_virtual() 
> is passed by pointer.  Since the compiler could not prove that the value 
> pointed to by "data" would not be manipulated in the write_virtual() 
> functions, it could not make this substitution that you have made by hand.
>
> As an alternative, one could also change the parameter in 
> write_virtual_word() to "const Bit16u* const data", for example.  This 
> would allow the compiler to remove the temporaries as well since it 
> knows the const'ness of the parameter being passed.  Also, the current 
> changes that you propose are not safe against a bug in write_virtual() 
> that may try to manipulate (*data).
>
> Just a thought.
> Brian
>
> Conn Clark wrote:
>
> > Hello All,

<SNIP>

> >


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Conn Clark
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Electronic Systems Technology Inc.              www.esteem.com

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