Re: [f-cpu] RC5, F-CPU and srotl

["Christophe" <christophe.avoinne@laposte.net>]

----- Original Message -----
From: Yann Guidon <whygee@f-cpu.org>
To: <f-cpu@seul.org>
Sent: Tuesday, April 16, 2002 7:12 PM
Subject: Re: [f-cpu] RC5, F-CPU and srotl


> hi !
>
> Christophe wrote:
> > I knew FORTH as being in fact a mix of compiled and interpretable code :
> forth is always more than one can think of, one reason is because the
> coding density is extremely high : the code is both the source and the
> executable, it is highly reflective (in a certain way, it codes itself)
> and there are a lot of sophisticated techniques that are mixed at every
levels.
> It gave me some headaches and sleepless nights when i was young and i stayed
> with Turbo Pascal instead :-P IIRC, when Forth "compiles" code, it's often a
> "condensed" representation of the existing modules, something like :
> putting each code module together (copy and paste) and remove the jumps
> at the ends, or something like that. The "win" is because the linked list
> search is not performed all the time. Today, one would use gperf and
> sophisticated hash tables instead...
>

:-)

> > Usually, a FORTH code is a sequence of call addresses (there is no opcode
but
> > just address), so it is more compact than a native code.
> it is certainly faster than looking up all the symbols in the linked lists
:-)

I'm not speaking about a text interpretor but a code interpretor.


My code is a FORTH code interpretor (when you run your FORTH code) but it seems
to have some error so i will reput it when errors are gone :)

>
> i don't understand your asm code. There is probably a misunderstanding with
> the jumps : the destination address is the 2nd operand. I see for example
> >     if (r61 == 0) jump r0,r55
> which means that you jump to the address stored in register zero, which
contains zero,
> and you save IP+4 to R55. The "trick" to remember is that
>  - the condition is at the left
>  - the pointers are in the middle
>  - the destination is at the right
>

ok sorry, i invert the thing

> > I did create a virtual machine, that is, a FORTH-like CPU. That was great
but
> > not the point for F-CPU.
>
> i don't understand (i know i should sleep but you know me :-D)
> you did this now, or you have done this in another context ?

when i was in University. I simulate in C a FORTH-like CPU. Not exactly a FORTH
langage but a machine code working with data and code stacks instead of
registers...

> i remember when i was 16 : i wanted to make a Forth machine using Turbo
Pascal
> and it soon became a nightmare. it's certainly easier to do this in F-CPU
asm.
> But a "synthesised" Forth code (not just a play with the code entry
addresses)
> will be much more efficient because it will unwind the data dependencies and
> allocate more registers, jump much less and make parallel things.

Sure, making it for a traditionnal CPU is not the best thing to do ;)



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