I am currently working on reintroducing GHDL into Debian. It is a VHDL compiler/simulator that includes non-standard VHDL libraries from various vendors and I have to throw out most of them (unlike before, it now comes with the core standard libraries reimplemented under a free license). I'm now unsure whether I should keep the Synopsys libraries which found some wider use before its features were finally offered by the VHDL language standard.
Here is the copyright statement and license from one of the files in its entirety: | Copyright (c) 1990, 1991, 1992 by Synopsys, Inc. All rights reserved. | | This source file may be used and distributed without restriction | provided that this copyright statement is not removed from the file | and that any derivative work contains this copyright notice. It offers use and distribution without restriction, but technically not explicitly modification. However, if permission of modification weren't intended, the requirement of keeping the copyright statement would be pointless. Therefore I am leaning towards permission of modification being implied. Keeping these files would be "nice to have" but not a requirement. Users with legacy VHDL projects using Synopsys libraries would need to find and install these libraries themselves if they were removed.