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From: Krishna Myneni <krishna.myneni@ccreweb.org>
Newsgroups: comp.lang.forth
Subject: Re: exercise in double number arithmetic
Date: Sun, 7 Jul 2024 20:02:37 -0500
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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