is there a free/trial version for ida's decompiler plugin?

Meta question. There are many questions on this site that asks to reverse engineer a specific transformation algorithm, and only finitely many input/output pairs are provided, such as reverseengineering.stackexchange.com/q/19090. Are they allowed, and what makes them clear enough?

@blabb I imagine this is doable with windbg reverseengineering.stackexchange.com/questions/19109

@user202729: as long as enough info is provided, sometimes the relationship can be discovered

some of these questions are answered, some are not