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<== Date ==> <== Thread ==>

Subject: Free GDCT and Alpha/Digital Unix
From: Tony Cox - (415)926-3105 <tcox@ssrl01.slac.stanford.edu>
To: tech-talk@epics.aps.anl.gov
Date: Tue, 18 Jul 1995 12:20:45 PST
Hi Gang,

	I've finally managed to get Free_gdct running on my Alpha/Unix box.
This was quite a struggle, but it is now running. There were a number of
interrelated problems which took some weeks to sort out:-

	o - Interviews `as is' (including the so-called Alpha patch on
	    interviews.stanford.edu) does not work on Alpha/Unix systems. In
	    fact, it will not work on ANY system in which sizeof(int) !=
	    sizeof( void*). This I have now fixed, at least as far as any
	    routines called by free_gdct are concerned. The patches should
	    work for other 64 bit Unix implementation, as long as the compilers
	    can represent all pointers as long's. If new c++ implementations
	    do other funny stuff (such as sizeof(void*) != sizeof( (class::*)())
	    then all bets are off.

	o - Free_gdct needs some conditional code for Alpha compilation - 
	    mainly in class definitions derived from the InterViews classes
	    which have virtual functions. I've worked with Jim on this & I'll
	    be sending him the patches for the next EPICS release.

	o - The Alpha iostream library is broken when it comes to some
	    pathological cases. I'm not sure if this is an Alpha bug, of if
	    it is InterViews playing fast and loose with the specs. The
	    particular offending construction is 

			(signed) int i;
			out << i	// saving databases
			....

			in >> i		// restoring

	    when i = -1. iostream dumps this as 4294967295 (treating it as
	    an unsigned int), but correctly restores its value. However, the
	    Alpha iostream library uses this as an excuse to loose
	    synchronization on the input file stream, completely
	    misinterpreting any further information in the database file
	    and ultimately causing a core dump (naturally, millions of
	    instructions later, and when it has managed to bury itself in
	    a stack which is 38 levels deep). Stuff like this always happens
	    in the summer when it is nice outside doesn't it?


So, we now have a working gdct on a 64 bit system; DCT is no longer
necessary for Alpha EPICS. We do, however, have to face the fact that 
InterViews is a dead product, and porting to other architectures (when Sun/HP
get around to their own 64 bit Unix's) is likely to be time consuming.

Does anyone know the status of Fresco? I believe that it will be distributed
as part of X at some time. It is supposed to be a development of (but not
a superset of) InterViews, and so could presumably function as a basis for
an enhanced GDCT. It may even be painlessly portable...

Tony Cox

--------------------------------------------------------------------------------
Dr Anthony D Cox
Computer Systems Specialist
Stanford Synchrotron Radiation Laboratory
Stanford Linear Accelerator Center
MS 69, Box 4349
Stanford CA 94305
tcox@ssrl01.slac.stanford.edu
--------------------------------------------------------------------------------


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