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From: David Kuehling <dvdkhlng@gmx.de>
Newsgroups: comp.lang.forth
Subject: Re: VFX code quality
Date: Tue, 22 May 2012 14:06:14 +0200
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>>>>> "Paul" == Paul Rubin <no.email@nospam.invalid> writes:

> "Elizabeth D. Rather" <erather@forth.com> writes:
>>> : z* ( a b c d -- ac-bd bc+ad ) .... ;
>> 
>> I don't understand your stack comment (I'm no mathematician)

> ac-bd just means a*c minus b*d.  So the word takes 4 parameters
> a,b,c,d representing the two complex numbers a+bi and c+di.  It
> multiplies them leaving the single complex number (ac-bd) + i*(bc+ad),
> as two coefficients on the stack.  It's trivial with locals:

>   : z* { a b c d -- x y } a c * b d * - b c * a d * + ;

> doing it without locals seems quite inconvenient.  I think Chuck might
> have used globals.

Well not too inconvenient, this is what I came up some time ago:

: z*  ( n1 n2 n3 n4 -- n5 n6 )
   2OVER 2OVER
   -ROT r* -ROT r* r+  >R  ( imag  )
   ROT r* >R r* R> r-      ( real )
   R> ;

this is for single-cell entities.  Of course with floats you can't use
>R R> which would screw you (but on the other hand floating point locals
aren't supported by the standard).

David
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