Re: exercise in double number arithmetic

On 7/10/24 08:08, dxf wrote:

On 10/07/2024 6:41 pm, dxf wrote:

On 10/07/2024 5:51 pm, Gerry Jackson wrote:

>
[...] I found I had another definition for D/MOD from Forth Dimensions Vol 14 Issue 6, p 27 "Math - Who Needs It"
https://www.forth.org/fd/FD-V14N6.pdf
I've no idea how good it is

  Here's the source file (32MATH.SEQ) for those interested:
>
https://pastebin.com/mfU8FZ1x

 Here's one I had lying around.  Not sure if I used it so may require checking
first!  The 2variable is an eye-sore.  Perhaps someone can eliminate it without
resorting to locals :)
 2variable d
 \ Divide quad by double. Unsigned.
: DUM/MOD ( uq ud -- udrem udquot )
   d 2! [ 16 cells ] literal 0 do
     dup >r  2swap  dup >r  d2*  2swap d2*
     r> 0<  dup d-  2dup d 2@  du< 0=  r> 0<  or
     if  d 2@ d-  2swap 1 0 d+ 2swap  then
   loop  2swap ;
 \ Divide doubles. Unsigned.
: DU/MOD ( ud1 ud2 -- udrem udquot )
   0 0 2swap dum/mod ;
 \ Divide doubles. Signed. Symmetric.
: D/MOD ( d1 d2 -- drem dquot )
   2 pick  2dup xor 2>r  dabs  2swap dabs
   2swap du/mod  r> 0< if  dnegate  then
   r> 0< if  2swap dnegate 2swap  then ;
 

This is interesting. I had recently implemented the non-standard word UD/MOD based on the corresponding word in Gforth. Thus, I have the double length division words,
UM/MOD ( ud u -- urem uquot )
   standard word for dividing unsigned double length by single length;
   return unsigned single length remainder and quotient.
UD/MOD ( ud u -- urem udquot )
   non-standard word for dividing unsigned double length by single;
   return unsigned single remainder and double quotient.
UM/MOD can have an overflow, while UD/MOD cannot overflow, but neither of the two words above can divide two double length numbers. The DUM/MOD and D/MOD words do what I'm looking for, in principle -- I don't know if they actually work. We need some tests. Also, the word naming doesn't seem to follow any real convention and the operation of each word can't be discerned from the name.
--
Krishna