[GAP Forum] Dangerous bug in Saving Workspaces (was "using GAP workspace")

Steve Linton sal at dcs.st-and.ac.uk
Tue Nov 2 12:23:47 GMT 2004

Dear GAP Forum,

A few days ago Alex Makosi reported problems with certain objects in a 
saved GAP workspace not loading correctly. It turns out that the cause of this
problem is the code that saves Boolean lists (blists). Any blist with more than
32 entries would almost certainly not be saved correctly, and might load with
wrong values or even as a completely corrupt object. This bug has been present
in all releases of GAP 4. 

A fix for this problem is available and will be included in release 4.4.4 due
in a few days. However, all workspaces created by SaveWorkspace up to now must
be regarded as suspect. Boolean lists are used quite widely in the library (for
instance in the code for transversals of subgroups of permutation groups), so
you may be using them even if you do not think you are. We must therefore
recommend that you recheck any results created using data from saved workspace
if you have any reason to doubt them.

We apologize for any inconvenience caused by this problem.

	Steve Linton 

Steve Linton	School of Computer Science  &
      Centre for Interdisciplinary Research in Computational Algebra
	     University of St Andrews 	 Tel   +44 (1334) 463269
http://www.dcs.st-and.ac.uk/~sal	 Fax   +44 (1334) 463278   

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