Re: ff-interface: defcstruct

[bill@cambridge.apple.com (Bill St. Clair)]

At  8:19 AM 9/26/93 +0100, Tobias Kunze wrote:
>while trying to port code running under franz lisp on the Next i get
>into troubles with mcl's ff-interface.
>the main point is that i need some kind of defcstruct facility, that is,
>machinery to deal with structures on the c side from within lisp:
>accessors should be provided for every c-side structure field, even for
>fields of embedded structures, and for elements of arrays that are
>referred to via pointers.

MCL's DEFRECORD should do the trick. Unfortunately, there is no automatic
translation facility for C header files (though we do have one for Pascal
header files).

>secondly, i'm having hard times to figure out how to pass floats and 
>doubles back and forth to C and Lisp; the manual has only a %copy-float
>function and everything from %get/%put-byte to -long.

There are a couple of undocumented accessors for floats in the foreign
function library (available after you (require "FF")). I sent out
some info about them a few weeks ago:

To: lam@ai-pluto.jpl.nasa.gov (Ray Lam)
From: bill@cambridge.apple.com (Bill St. Clair)
Subject: Re: Accessing C floating point data type in MCL
Cc: info-mcl
Bcc: 
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At  4:26 PM 8/26/93 -0800, Ray Lam wrote:
>Hi,
>                                I'm looking for a function simular to "%get-long" but it will work on 
>a ptr to a floating point number in C. I was looking into the
>ff-source.lisp
>file and found the function "%get-x2float". Can anyone tell me what that
>function does?

(ccl::%get-x2float ptr)
  Reads a 10-byte IEEE extended float from ptr and returns it as an
MCL 8-byte float.

(ccl::%float2x float ptr)
  Stores the 8-byte MCL float as a 10-byte IEEE extended float at ptr.

(defun %safe-get-double (ptr)
  ; Reads an 8-byte IEEE double float from ptr and returns an 8-byte MCL float
  (let ((float (ccl::%copy-float 1.0)))
    (ccl::%get-double ptr float)
    float))

(ccl::%put-double flt ptr)
  Stores the 8-byte MCL float as an 8-byte IEEE double float at ptr.