Re: exercise in double number arithmetic

On 7/7/24 15:52, mhx wrote:

OK, let's extend it a little.
 : CHS ( M N -- M!/{M-N}!/N! )
     DUP local  N
      -  local M-N
     1.  N 1+ 1 DO  M-N I +  I  M*/  LOOP ;
 

Great! My non-locals version is
\ Compute binomial coefficient as a double length number
: binom ( n k -- d )
     dup >r - 1 s>d
     r> 1+ 1 ?DO
       2 pick I + I m*/
     LOOP  rot drop ;
130 65 binom d.
95067625827960698145584333020095113100  ok
This provides a nice example for use of double length number computation, thanks to Albert.
As a side benefit to this exercise, I discovered that my division overflow check in kForth's M*/ (and in the non-standard UTM/ used by M*/) was not correct. This has been fixed in kForth-64.
--
Krishna