Re: [Flashforth-devel] For-next loops - the New Design

[Mikael N. <mik...@fl...>]

Igor,
I don't think your HW arguement really works.

I had to introduce an extra "high level intelligence" branch and 
decrement to get the desired behavior.
See my previous post for that.

Also if you bother to take a look at the HW loops inside the PIC24/33 ( 
DO-LOOP and REPEAT )
these all loop N+1 times. Just because it is efficient in HW.

But from a programmer point of view I think it is good to make the 0 
FOR2 .. NEXT to loop $10000 times.

0 FOR .. NEXT will loop 0 times. I rely quite a bit on this in many 
places.

Still I am not convinced that the FOR2 is needed that much, so it could 
be left out also.
Most loops that I use are way smaller than $10000 times.
In your special case you can do that $10000 time loop with BEGIN UNTIL

BR Mike

On 28.05.2015 16:11, om1zz wrote:
> Peter,
>
> long time back (2009-10??) there was no do-loop implemented, and we
> had discusions about that, afaik.
> The reason was it was difficult to implement, heavy and therefore 
> slow.
>
> Instead of that, Mike did FOR, which is very fast, as it does just a
> single instruction check when passing index to zero.
>
> That introduces the bug (my interpretation) which has not been
> discovered till today (why?).
>
> Mike has written the do-loop recently (as the external .txt source)
> for compatibility reasons (as I claimed long time back mainly because
> my intention with floating point library which uses do-loop, and
> others).
>
> Forth is a "better assembler" or "clever assembler" used today for
> low level programming on hardware.
>  No high-level elements there. Just a simple puzzle.
>
> When working so close to the HW you must admit the hw-specific
> behaviour of the forth.
>
> So - shooting a zero into a loop means it will underrun (within the
> size of the basic cell, here 16bit) and loop over till zero (65536x).
> That is normal, and this is how the MCU works (all of them, PIC, AVR,
> ARM, MIPS, x86, etc).
>
> Pushing any "high-level intelligence" into the forth's primitive,
> basic, fundamental words changes the forth into a Frankenstein.. :)
>
> Igor,
> assistant to Mr. F.
>