[Oberon] Assumed issue in the Lola-2 compiler

Jörg Straube joerg.straube at iaeth.ch
Mon Apr 15 03:13:12 CEST 2019

The Lola compiler at https://inf.ethz.ch/personal/wirth/Lola/index.html does not handle CONSTs with length correctly. To enable them you have to add two statements to factor0() in LSC.Mod:

IF sym = LSS.ident THEN
   x := ThisObj(LSS.id); LSS.Get(sym);
   IF x.tag = LSB.var THEN selector(x)
   ELSIF x.tag = LSB.const THEN
      n := x.b.val; len := x.b.size;
      NEW(x); x.tag := LSB.lit; x.val := n;
      x.type := LSB.integer; x.size := len
   ELSE LSS.Mark("bad factor") END
ELSIF sym = LSS.lparen THEN


> Am 15.04.2019 um 02:18 schrieb "rochus.keller at bluewin.ch" <rochus.keller at bluewin.ch>:
> Thank you once more for your feedback.
> @ Paul Reed:
>>> if x=-1, then I would assume the result of this assignment would be zero.
>>> Unfortunately, yes.
> Ok, then DIV is not a useful operator for this case. I therefor changed the REPEAT statement like this:
>    REPEAT d[i] := x MOD 10H; 
>        x := ASR(x,4);  (* 'x DIV 16' corresponds to ASR(x,4) *)
>        INC(i) 
>    UNTIL (x = 0) OR (i = 8);
> I did a couple of tests and think it works as expected. Does this look reasonable to you?
> @ Joerg Straube:
> I hope you don't mind if I respond in English ;-) 
> Thanks for the minimized MOD expressions; I will do some tests with them. Currently I assume that my Oberon to C++ translator will just insert _MOD() funktion calls and not prescribe the implementation. I agree that the language report is rather brief and more information would be helpful. But the ' length specification is explicitly mentioned in the text which for me is sufficient to support it; and the reason I spent the effort with the Oberon to C++ translator was that I can use the original Lola compiler source code. It is also easier to recognize the literals in the generated Verilog code if the format doesn't change too much.
> Best
> R.K.
> --
> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon
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