Procedures vs Functions

[flyway38]

Hi all,

Always had this doubt about efficiency in choosing Procedure or Function for structuring my code. I know how to use them by experience in coding JAL for many years.

Another doubt is declaring VARs inside Procedures or Functions will make them slower or not..., so here goes the questions;

1) - Which is the fastest/ efficient at runtime (Procedure or Function) ?

2) - Declaring VARs inside Procs/Funcs will make them slower ?

Thank you very much

Kind regards,

Filipe Santos

[Oliver Seitz]

Hi Filipe,

I can tell you für 2): No. At compile time, the variable name is replaced by a fixed memory address. There's no difference if the name is declared inside a procedure/function or in the main program. There is, however, a little space ("access RAM") which contains a bit "faster" variables. So, it can make a little difference if a variable is declared earlier or later in a program.

8-bit PIC controllers are a bit special, as in a sense they don't have RAM at all, they merely have up to several thousand processor registers. Accessing (simple, not array) variables is therefore very fast compared to other processor architectures. 

Greets,

Kiste

Am Sonntag, 21. August 2022, 12:49:39 MESZ hat flyway38 <fsfo...@gmail.com> Folgendes geschrieben:

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[flyway38]

Hello Kiste,

Thank you for your input.

Cheers,

FS

[Rob CJ]

Hi Filipe,

About 1). I am not sure, you should have a look at the assembly code. If you would replace a function by a procedure then you should have at least one parameter of the type 'out'. There is a way to speed up a function or procedure by declaring it 'inline'. If you do that the procedure or function is not called but the code is copied into the program where it is used. This increases the code size of your program but saves you a call to the procedure or function.

And if you use interrupts there is an option 'fast' to speed it up but I never used it and you need to take some precautions if you use that.

Kind regards,

Rob

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Van: jal...@googlegroups.com <jal...@googlegroups.com> namens flyway38 <fsfo...@gmail.com>
Verzonden: zondag 21 augustus 2022 13:46
Aan: jallib <jal...@googlegroups.com>
Onderwerp: Re: [jallib] Procedures vs Functions

 

To view this discussion on the web visit https://groups.google.com/d/msgid/jallib/365d7bab-9091-4ac5-b55f-265f5cd23104n%40googlegroups.com.

[vsurducan]

I think sometimes whichever you will use procedure or function will not be fast enough. One bad example is too long if...end if procedures containing stuff you are not using it. The common answer you'll get is that compiler will delete unused stuff, which is correct unless it' s about defined registers. So when you have time constrains, already defined procedures that you get from the libraries have to be modified and simplified on your own need. This is totally against the jallib policy :) but is the only way which works. One good way is to check frequently the code length when major revisions occure. A simple pass of a variable from one procedure to other or from a function to a procedure may substantially increase the code length. Too structured source code in which you call a procedure from another procedure and from another one is increasing the used stack. Sometimes repeating a portion of code is much better than calling it within a procedure. And so on,  things you will discover by yourself...

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[flyway38]

Nice tips here.

Thank you Rob and Vasile.

Cheers,

FS