[Oberon] Numerical CASE Statements in Project Oberon

[Jörg Straube]

Yes.
The compiler uses the instruction Put3(BR, 7, reg) eg for returns from procedures.
Jörg

Am 23.10.2016 um 05:46 schrieb Chris Burrows <chris at cfbsoftware.com>:

>> -----Original Message-----
>> From: Chris Burrows [mailto:chris at cfbsoftware.com]
>> Sent: Saturday, 7 November 2015 11:33 PM
>> To: ETH Oberon and related systems (oberon at lists.inf.ethz.ch)
>> Subject: Numerical CASE Statements in Project Oberon (was: [Oberon]
>> RISC.img)
>> 
>>> 
>>> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of
>>> Jan de Kruyf
>>> Sent: Friday, 6 November 2015 8:37 PM
>>> To: Paul Reed; ETH Oberon and related systems
>>> Subject: Re: [Oberon] RISC.img
>>> 
>>> 2. Question:
>>> I see that the 'numerical' CASE implementation is missing in
>> ORP.Mod,
>>> although it is in the language spec and although we might
>> reasonably
>>> expect people to port programs from O2 to O7.
>>> 
>>> Would it be in the interest of the community for me to try and
>>> implement that part, at least for constant labels?
>>> 
>> 
>> Don't even think about implementing it unless you are planning to do
>> it properly - a half-baked solution would be worse than none. e.g. I
>> would expect a complete solution to include the implementation of a
>> RISC6 (or RISC5.1 maybe?) processor which has indexed-branch
>> statements.
>> 
> 
> I have now implemented a numerical CASE statement in Astrobe for Embedded Project Oberon for compatibility with the Oberon compiler used in Astrobe for the ARM-Cortex targets. 
> 
> I was wrong about the RISC5 processor instruction set. It does not need any additional instructions in order to be able to implement an efficient branch table-driven numerical CASE statement. It already has a branch instruction that sets the address of the next instruction to be the value of a register. The index into the jump table can be computed and stored in that register. 
> 
> Apologies for any confusion,
> 
> Regards,
> Chris
> 
> Chris Burrows
> CFB Software
> http://www.astrobe.com/RISC5
> 
> 
> 
> 
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