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From: Mitch.Bradley@ENG.SUN.COM (Mitch Bradley)
Newsgroups: comp.lang.forth
Subject: Re: Memory Management/PIC
Message-ID: <9106041629.AA13342@ucbvax.Berkeley.EDU>
Date: 4 Jun 91 16:21:17 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Mitch Bradley <Mitch.Bradley%ENG.SUN.COM@SCFVM.GSFC.NASA.GOV>
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Organization: The Internet
Lines: 37

> In BASIS, ALIGNED must be used as a runtime operator, to match the compiled
> ALIGNments.

I disagree.  It is possible to perform the ALIGNED operation at compile time,
storing the result either in a constant or in a definition with LITERAL .

Here's how I do data structures:

   : STRUCT  0  ;
   : CELL:  ( offset -name- offset' )  CREATE  ALIGNED  ,  CELL+  DOES> @ +  ;
   : CHAR:  ( offset -name- offset' )  CREATE           ,  CHAR+  DOES> @ +  ;

   STRUCT
      CHAR: >FIELDA
      CELL: >FIELDB
   CONSTANT /MYSTRUCT

   CREATE MYSTRUCT1  CHAR q C,  ALIGNED  1234 ,
   CREATE MYSTRUCT2  CHAR z C,  ALIGNED  5678 ,

   : .MYSTRUCT  ( adr -- )  DUP >FIELDA C@ EMIT  ( adr ) >FIELDB @ .  ;

   MYSTRUCT1 .MYSTRUCT
   MYSTRUCT2 .MYSTRUCT


This illustrates a fairly typical case in which alignment is required -
user-defined data structures with mixed-size fields.  All the alignment
is done at run time.  It can be done without the structure defining words:

   : .MYSTRUCT  ( adr -- )
      DUP C@ EMIT   ( adr )  [ 1 CHARS ALIGNED ] LITERAL +  @ .
   ;

Note that the ALIGNED step is again performed at compile time.

Mitch