[Oberon] Negative integer literals in Oberon

[Chris Burrows]

Just one example I can think of is that I've stored a HEX value representing an absolute start address into an INTEGER and then incremented it to initialise a block of memory at that address.

Something like this:

VAR
  startAdr, nWords, data: INTEGER;

...
  FOR startAdr := 0ABCDEFH TO (startAdr + nWords) BY 4 DO ReadInput(data); SYSTEM.PUT(startAdr, data) END

Regards,
Chris Burrows
CFB Software
https://www.astrobe.com


> -----Original Message-----
> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of Jörg
> Sent: Tuesday, 28 April 2020 6:42 PM
> To: ETH Oberon and related systems
> Subject: Re: [Oberon] Negative integer literals in Oberon
> 
> Wojtek
> 
> There is no question, that hex notation is convenient and needed.
> But are we really talking about INTEGERs here? Whenever I saw hex
> notation in my career, it had something to do with HW registers and silly
> register constants for low level programming.
> - INTEGERs and REALs are abstractions to do calculations with undefined
> precision.
> - POINTER is an abstraction to address memory
> - SET is an abstraction for bit operations.
> 
> To what Oberon type should the hex notation apply?
> In my point of view to INTEGERs the least. SET the most, but this is not
> foreseen today.
> And POINTERs have no explicit value at all, as all is abstracted away
> (hidden) by NEW()
> 
> br
> J rg
> 
> ?Am 28.04.20, 06:51 schrieb "Oberon im Auftrag von Skulski, Wojciech"
> <oberon-bounces at lists.inf.ethz.ch im Auftrag von
> skulski at pas.rochester.edu>:
> 
>     Joerg:
> 
>     >It s a good point but a little bit a corner case. Principally,
>     > Oberon does not know addresses, as addresses are abstracted
>     > away by the type construct POINTER TO
> 
>     Yes, POINTER TO needs to be used eventually. But we are facing the
> question
>     how to assign the hard coded address to the POINTER. The VRAMORG is
>     the case in point. This address is connected to the firmware video
> controller.
>     The value has to be used as provided below, or there will be no
> video.
> 
>     VRAMORG does not have to be coded in hex in Oberon. The FW developer
> can use
>     0E7F00H, while the Oberon programmer can write 950016 in decimal. But
> it is
>     much easier and less error prone if both developers can use the same
> notation.
>     So we need the hex in this case because firmware developers are
> likely to use hex.
> 
>     Another example is perhaps all these protocols like Ethernet where
> the documentation
>     will provide hex constants. Imagine the Oberon developer not being
> able to use these,
>     but rather using a Windows calculator to translate to decimal because
> hex notation
>     was removed from the language.
> 
>     Wojtek
> 
>     br, J rg
> 
>     > Am 27.04.2020 um 22:40 schrieb Skulski, Wojciech
> <skulski at pas.rochester.edu>:
>     >
>     > ?Joerg:
>     >
>     >> Could somebody give me a good example, where INTEGERs need a hex
> notation?
>     >
>     > How about this? These INTEGERS represent addresses. Are addresses
> integers? I believe they are. The memory is a collection of addresses
> with consecutive numbers expressed with integers. So it is a relevant
> example.
>     >
>     > (* Memory map; PO.System page 104 *)
>     > STACKSIZE* = 8000H;      (* 32 kB. Was hardwired in Kernel.Init *)
>     > STACKORG*  = 80000H;   (* stackOrg = 524,288; half a megabyte. *)
>     > HEAPORG*   = STACKORG; (* heapOrg = stackOrg *)
>     > FSoffset*  = STACKORG;     (* Not clear what it is *)
>     > MEMLIM*    = 0E7EF0H;     (* 1 MB minus 98,575 bytes of VRAM at the
> end*)
>     > VRAMORG*   = 0E7F00H;   (* start of memory-mapped display frame*)
>     > VRAMSIZE*  = 1024*768 DIV 8;     (* 1024 x 768 pixel, monocolor
> display frame*)
>     > --
>     --
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> 
> 
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