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TG9541 / stm8ef

STM8 eForth - a user friendly Forth for simple µCs with docs
https://github.com/TG9541/stm8ef/wiki
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DNEGATE doesn't in v2.2 #13

Closed RigTig closed 7 years ago

RigTig commented 7 years ago

\ I am having great fun using eForth \ thank you for a great piece of work \ In v2.2 3 0 dnegate .s \ results in FFFD 0 <sp ok \ when it should be FFFD FFFF <sp ok

\ regards, RigTig

TG9541 commented 7 years ago

Hi RigTig, I can conform he problem. It has nothing to do with my meddling with Dr. C.H. Tings code: it's already present in STM8EF V2.1. So far I didn't use double arithmetics much, and it's a good thing that you're testing it.

TG9541 commented 7 years ago

Hi RigTig, it's fixed in the develop branch. In case it's needed in the master branch before release of STM8EF V2.2.7 please use the following definition as a work-around:

: DNEGATE NOT >R NOT 1 UM+ R> + ;

Thanks again for reporting this issue :-)

Regards & Greetings from Germany, Thomas

RigTig commented 7 years ago

Thomas, Many thanks for fix. All I'd done was figure the high byte was too high by 1, so my temporary fix was just : DNEGATE DNEGATE 1- ;

anyway, just so you have an integer square root when you need it, here is one algorithm coded in eForth

\ some maths utility words \ eForth + is u+ : u+ ( n n -- u ) + ;

: dnegate ( d -- -d ) \ fix for bug in v2.2 dnegate 1- ;

: ud+ ( ud ud -- ud ) ( l h l h )

r rot um+ ( h d ) rot u+ ( d ) r> u+ ; : d- ( d d -- d ) \ 2do: ensure works on full range dnegate ud+ ; : d> ( d d -- f ) d- swap drop 0< not ;

: isqrt ( d -- n ) $8000 ( d c ) $8000 ( d c g ) begin dup dup um* ( d c g g^2) 6 pick 6 pick ( d c g g^2 d ) d> if ( d c g ) over xor then ( d c g ) swap 2/ $7fff and ( d g c ) dup 0= if drop rot rot 2drop -1 ( g true ) else swap over ( d c g c ) or 0 then until ;

The only trick here is to do a right bit shift by one bit, I've used the 2/ (which accepts positive and negative integers) and co-opted it by just dropping the sign bit ( $7fff and ).

During my testing, I had the following line just after the 'begin' cr 2dup . . \ g in col1 and c in col 2 Interesting to watch how the result gets refined.

For the record, here is the C program I used as the source of the algorithm unsigned int sqrt32(unsigned long n) { unsigned int c = 0x8000; unsigned int g = 0x8000;

    for (;;) {
        if (g*g > n) {
            g ^= c; # Bitwise exclusive OR
        }

        c >>= 1;  # Right bit shift

        if (c == 0) {
            return g;
        }

        g |= c;  # Bitwise inclusive OR
    }
}

Please keep up the good work Regards, RigTig

On Mon, Feb 13, 2017 at 4:54 AM, Thomas notifications@github.com wrote:

Closed #13 https://github.com/TG9541/stm8ef/issues/13.

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/TG9541/stm8ef/issues/13#event-958721235, or mute the thread https://github.com/notifications/unsubscribe-auth/AWVRezIkQan1xwjHG3pxhqKmRQtclvDjks5rb0c4gaJpZM4L-d__ .

TG9541 commented 7 years ago

Hej RigTig,

I tested the code you posted: it works great, but 256 0 isqrt . returns 15, clearly a rounding error. Adding the line 1 0 ud+ to isqrt fixes this :-)

Would it be OK to add the code to a lib section in the STM8EF repo under a (permissive) OS license?

RigTig commented 7 years ago

Thomas, Be my guest. It is the least I can do given that I got the algorithm from the net and your efforts underlie what I did anyway. Well spotted about the shortcoming. I am working on a simple GCODE interpreter for a 3D printer and I think it'll just fit onto STM8. If so, I'll be using an ESP14. I have thoroughly enjoying exploring the inner workings of stm8ef. Thank you for your public contributions too.

Regards, RigTig

On 20 Feb 2017, at 07:19, Thomas notifications@github.com wrote:

Hej RigTig,

I tested the code you posted: it works great, but 256 0 isqrt . returns 15, clearly a rounding error. Adding the line 1 0 ud+ to isqrt fixes this :-)

Would it be OK to add the code to a lib section in the STM8EF repo under a (permissive) OS license?

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

TG9541 commented 7 years ago

Thanks :-) I had never thought that one would actually consider moving the limits of what a tiny micro can do that far! This project sounds like a fun - I'm looking forward to more feedback!

RigTig commented 7 years ago

Tested the isqrt and confirmed the bug. A little bit of exploring found the culprit: d> was actually d>=. So here is a new d> that seems to be ok now, and you'd never guess that isqrt actually gives 16 as the answer for 256 0 isqrt .

: d> ( d d -- f ) d- 2dup or 0= ( d f ) rot rot 0< swap drop or not ; Thanks Thomas, and please keep up the good work. Regards, RigTig

TG9541 commented 7 years ago

@RigTig

Great, thanks! I had chiefly looked in the same direction but I falsely assumed that d>= was intentional :-)

As the GitHub issues appear to work great as a discussion platform!

Here is something that might be relevant for your G-code project and also for lib/math:

trigonometry & fractional arithmetics:

I've got no experience with fractional arithmetics (only fixed point), I guess that I should start experimenting a bit. CORDIC used to be widely used (there is even a MCS51 µC, the XC886, with CORDIC hardware for field oriented motor control).

Another that needs solving is a "uploader" program, ideally one that does includes, and that attempts to be smart (i.e. one that tests whether a library has already been loaded). AmForth has an interesting solution, but I'm skeptical about doing constant replacement in the uploader.