FLI bug or pilot error?

Hello,

I've been working on a FFI for the MacOSX CoreMIDI framework and I've  
run into some strange behavior while trying to define types for the  
MIDIPacket and MIDIPacketList structures. The FLI doesn't seems to be  
calculating the offsets to members in a structure correctly.

The relevant C typedefs are:
==================================

struct MIDIPacket
{
   MIDITimeStamp	 timeStamp;
   UInt16	 length;
   Byte		 data[256];
};
typedef struct MIDIPacket MIDIPacket;


struct MIDIPacketList
{
   UInt32          numPackets;	
   MIDIPacket  	  packet[1];
};


The FLI definitions I am using are:
============================================

(in-package :cl-user)

(fli:define-c-typedef (uint16 (:foreign-name "UInt16"))
   (:unsigned :short))

(fli:define-c-typedef (uint32 (:foreign-name "UInt32"))
   (:unsigned :long))

(fli:define-c-typedef (uint64 (:foreign-name "UInt64"))
   (:unsigned :long-long))

(fli:define-c-typedef (midi-time-stamp (:foreign-name "MIDITimeStamp"))
   uint64)

(fli:define-foreign-type (:struct midi-packet :foreign-name  
"MIDIPacket")
     (&key (size 256))
   `(:struct
     (time-stamp midi-time-stamp)
     (length uint16)
     (data (:c-array (:unsigned :byte) ,size))))

(fli:define-foreign-type (:struct midi-packet-list :foreign-name  
"MIDIPacketList")
     (&key (length 1) (size 256))
   `(:struct
     (num-packets uint32)
     (packet (:c-array (midi-packet :size ,size) ,length))))


When I allocate a foreign object the FLI is calculating the address  
of the 'packet slot of the 'midi-packet-list as base address + 8  
bytes instead of the expected base address + 4 bytes (which is the  
size of a the UInt32 data type).

CL-USER> (setf x (fli:malloc :type 'midi-packet-list))
#<Pointer to type (:STRUCT MIDI-PACKET-LIST) = #x03F44C00>

CL-USER> (fli:foreign-slot-pointer x 'num-packets)
#<Pointer to type UINT32 = #x03F44C00>

CL-USER> (fli:foreign-slot-pointer x 'packet)
#<Pointer to type (:C-ARRAY (MIDI-PACKET :SIZE 256)) = #x03F44C08>

CL-USER> (- (fli:pointer-address *) (fli:pointer-address **))
8

If change the element type of the 'midi-packet-list 'packet slot to  
one of the immediate types the address of the 'packet slot is  
calculated as base address + 4 (which I expect). Try the following:

(fli:define-foreign-type (:struct midi-packet-list :foreign-name  
"MIDIPacketList")
     (&key (length 1) (size 256))
   `(:struct
     (num-packets uint32)
     (packet (:c-array :byte ,length))))


Is this a bug or am I missing something? I'm using LWM 4.4.6.

Thanks much,

-greg







_______________________________________________________
Greg Wuller                             greg@wuller.com
_______________________________________________________