bug#41279: 26.3; Calc: sum(gcd(0,n),n,-1,-1) evaluates to -1

[Mattias Engdegård]

15 maj 2020 kl. 19.44 skrev David Ongaro <david.ongaro@hamburg.de>:

> I see, so the simplest reproduction of the bug doesn't involve the sum, but 
> just the evaluation of gcd(0, x) or gcd(x, 0). Your fix seems sensible to me, 
> I don't see why you consider it a 'hack'. The simplification gcd(0, x)=gcd(x, 
> 0)=abs(x) seems legit and matches the gcd definition "The largest positive 
> integer that divides each of the integers".

Quite, but there is a small possibility that further simplification relies on 
the gcd(0,x)=x behaviour. You never know with Calc: it is complex and 
everything seems interconnected. After all, abs is often an obstacle in 
algebraic transforms; you often end up splitting cases.

That said, it's probably the right thing to do. Now pushed to master, which 
means that you need to build a development snapshot from source, or apply the 
change (60cd6cce55) to your Emacs.