[Oberon] FPGA - Bit reversal

[Jörg]

Wojtek

I think there is a misunderstanding.
Of course I know that bit positions are important. And Oberon can handle those.
But the point is portability. I don‘t talk about assembler code as it is per definition bound to the processor so not portable by definition.

I talk about higher level source code that has to be compiled to the CPU of your choice.

The Oberon complier offers you low level access to CPU dependent functionality. It does this by offering a pseude MODULE called SYSTEM. It’s not a normal module. Whenever you find a source code where this compiler module SYSTEM is imported you have a hint that most probably this code is NOT portable as it either depends on endianess, the underlaying OS Oberon runs on or other low level characteristics that you need to check if xou port your code to another machine.

So SYSTEM is good, as it allows low level bit access and in parallel hints the programmer on possible portability issues.

Now ORD() - as it is now in the Oberon report - is „evil“ as code using it might not work on other machines as it depends on lower layer characteristics (endianness, character encoding  used etc) WITHOUT hinting the programner on possible portability issues. The code compiles but might not work.

BTW: I‘m engineer and hate Windows :-)

Jörg

> Am 23.09.2017 um 15:38 schrieb Skulski, Wojciech <skulski at pas.rochester.edu>:
> 
> Evil?
> 
> If you want to manipulate bits, then you cannot escape the fact, they they have their positions within the word. The position depends on a platform. There is no such thing in the world like a computer which would not depend on bit positions. A processor status or setup depends on particular bits within registers, the video or audio depends on particular bits, and so on.
> 
> I see this discussion as yet another chasm between computer scientists and engineers. The former want to live in an ideal programming world where algorithms move from place to place without changing anything. For them, bit positions are ugly details to get forgotten. For an engineer the very notion that particular bits are not accessible is a sheer absurd.
> 
> I build and program hardware. I deal with bits every day. Anything what hampers my access to bits is an instant enemy. Our friends computer scientists should one day wake up to the fact that hardware has to be controlled by accessing particular bits in particular places. Having good tools for doing this is essential. These tools need to be nurtured rather than frown upon.
> 
> I know that Chris is on our side. He programs microcontrollers.  I am talking to the others who still think that Oberon only runs on a Turing machine. Or on Windows.
> 
> Thanks,
> W
> ________________________________________
> From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Jörg [joerg.straube at iaeth.ch]
> Sent: Saturday, September 23, 2017 9:03 AM
> To: chris at cfbsoftware.com; ETH Oberon and related systems
> Subject: Re: [Oberon] FPGA - Bit reversal
> 
> Chris
> 
> I know. ORD() is ‚evil‘ as I wrote in a previous mail. ORD(“S“) is not defined either....
> 
> Jörg
> 
> Am 23.09.2017 um 14:09 schrieb Chris Burrows <chris at cfbsoftware.com>:
> 
>>> -----Original Message-----
>>> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of
>>> Jörg
>>> Sent: Saturday, 23 September 2017 4:29 PM
>>> To: ETH Oberon and related systems
>>> Subject: Re: [Oberon] FPGA - Bit reversal
>>> 
>>> No, I disagree.
>>> So far Oberon isn t bothered with endianess.
>>> 
>> 
>> I'm not so sure ...
>> 
>> VAR
>> s: SET;
>> i: INTEGER;
>> 
>> s := {1,2,3);
>> i := ORD(s);
>> 
>> What is the value of i?
>> 
>> --
>> Chris
>> 
>> 
>> 
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