We are looking at an open source software's "General Public License" that says "if you distribute or publish a work containing modified software you must license at no charge to all third parties the whole of the work". For performance reasons, we would need to move functions in this software from a C file to a header file and make them static inline, and also remove (or handle differently) a few global variables, otherwise it can't run multithreaded.
Does this language (and/or GPL in general), apply to that level of modification ? Is there a minimum allowed level of modification defined anywhere, for example adding comments ?
Additional notes - this license says it's a General Public License but does not use the term "GPL". My objective is to learn whether, in general, GPL licenses allow any level of modification, even superficial such as comments, without requiring incorporating code to be freely published