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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Hans<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Generally - although defined in the language and not in module SYSTEM - code using ORD() is not portable.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">i := ORD(ch); (* is not portable as the charset is not defined in the Oberon-07 report *)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">i := ORD(bool); (* is not portable as the Oberon-07 reports does not define the representation of TRUE and FALSE *)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">i := ORD(set); (* is not portable as the bit numbering is not defined *)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Although not fully portable but doesn’t need SYSTEM, stay with CHR( ORD(ch) - ORD(“a”) + ORD(“A”) );<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Don’t be afraid of the complex looking ORD(“a”) + ORD(“A”), the compiler folds these constants into one value<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">br<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Jörg<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">Von:
</span></b><span style="font-size:12.0pt;color:black">Oberon <oberon-bounces@lists.inf.ethz.ch> im Auftrag von Hans Klaver <hklaver@dds.nl><br>
<b>Datum: </b>Dienstag, 9. August 2022 um 01:07<br>
<b>An: </b>ETH Oberon and related systems <oberon@lists.inf.ethz.ch><br>
<b>Betreff: </b>Re: [Oberon] Bit-fiddling: SETs and type casts in Oberon-07<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Chris, Jörg and Florian,<br>
<br>
Thanks for your answers. Now it makes more sense to me.<br>
<br>
I looked into these matters a bit more. <br>
<br>
It appears that Wirth's OR compiler always allows casts of 'scalar' types (here meaning all Oberon basic types) with SYSTEM.VAL to a type of the same or smaller SYSTEM.SIZE (narrowing casts), without warning. Widening casts (to a type with larger SYSTEM.SIZE)
are only possible via cast to BYTE and INTEGER. <br>
<br>
I suppose this is (as Florian wrote) because widening casts lead to 'undefined behaviour'. Well, I think the behaviour in cases of SYSTEM.VAL(SET, v) is only partially undefined: the part of the SET one is interested in (elements 0 .. 8*SYSTEM.SIZE(v)-1) is
quite well defined as long as it is guaranteed that element 0 of the SET is the least significant bit of the variable; the undefined part, the elements > 8*SYSTEM.SIZE(v)-1, should just be disregarded.<br>
<br>
The other two Oberon-07 compilers I checked (Astrobe for Cortex-M3 and OBNC) allow all casts of the basic types to and from each other, narrowing or widening; the Astrobe compiler gives a warning 'type cast !' with any use of SYSTEM.VAL.<br>
<br>
Chris wrote:<br>
<br>
> The Oberon-07 report states:<br>
> <br>
> EXCL(v, x) is equivalent to v := v - {x}. (* where v is a variable not an expression *)<br>
> <br>
> Hence trying to write EXCL(SYSTEM.VAL(SET, ch), 5) would be equivalent to writing:<br>
> <br>
> SYSTEM.VAL(SET, ch) := SYSTEM.VAL(SET, ch) - {5} <br>
> <br>
> To me, that is as wrong as trying to write something like:<br>
> <br>
> ORD(ch) := ORD(ch) + 1<br>
> <br>
> or INC(ORD(ch))<br>
<br>
<br>
Concerning this I found out that only OBNC requires a variable as first parameter of EXCL and INCL, and disallows SYSTEM.VAL in its place; Wirth's OR and the Astrobe compiler have no problem with SYSTEM.VAL as first parameter of these procedures. So for instance
they accept the following (Astrobe with a warning 'type cast !'):<br>
<br>
VAR i: INTEGER;<br>
...<br>
EXCL(SYSTEM.VAL(SET, i), 5)<br>
RETURN i<br>
<br>
This is in accordance with the language report: there it says that SYSTEM.VAL has the function of 'identity' (earlier described as 'x interpreted as of type T'); use of this function here can be equated with use of a variable.<br>
<br>
So I think that OBNC is a bit too restrictive in disallowing SYSTEM.VAL as first parameter of EXCL and INCL.<br>
<br>
Regards,<br>
<br>
Hans<br>
--<br>
Oberon@lists.inf.ethz.ch mailing list for ETH Oberon and related systems<br>
<a href="https://lists.inf.ethz.ch/mailman/listinfo/oberon">https://lists.inf.ethz.ch/mailman/listinfo/oberon</a><o:p></o:p></span></p>
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