Is my understanding on how my 0-based vector access works correct?

[hermann@stamm-wilbrandt.de]

In Elementary Number Theory lecture of Heidelberg University I learned a 
lot,
lately on continued fractions and Pell equations (script behind 
University VPN).

I implemented "fundsol(d)" in pell.gp below, to determine fundamental 
solution
of Pell equation x^2-d*y^2=1 per Corollary 6.42 of script.

From gemini.google.com I learned the PARI/GP way based on quaduint() to 
do that in fundpari(d).

With latest commit
https://github.com/Hermann-SW/uni-heidelberg/commit/7133265e4c49ebba99cfe98fef912ea17ba4588f

I implemented 0-based vector access so that fundsol() matches the 
Corollary a_i notation
that is 0-based for continued fractions (in proof the lecturer used -2 
based as well sometimes).

So bottom code works, an "a(i)" is able to access cf vector 0-based.
This worked only after quite some time and error.
I want to get confirmation or correction on my understanding.

When cf variable gets assigned it is allocated as global variable 
because it is not in "my(...)"?
a(i) then can access that global cf variable?


Unrelated, but might be helpful for people working with Graphviz.
For above lecture I developed "Latex labels for Graphviz" project as 
well:
https://gist.github.com/Hermann-SW/12c7644ac0c75b4eb019f76c3f023fe5

Regards,

Hermann.

hermann@8840hs:~/uni-heidelberg/scripts$ gp -q pell.gp
? for(i=2,80,if(!issquare(i),print1(fundsol(i)==fundpari(i))))
111111111111111111111111111111111111111111111111111111111111111111111111
? [x,y]=fundsol(21)
[55, 12]
? x^2-21*y^2==1
1
?

assert(b)={if(!(b),error())}

digmat(a)=[a,1;1,0];

find_first(v, x)={for(i=1, #v, if(v[i]==x, return(i));); return(0); }

a(i)=cf[i+1];

fundsol(d)={
  assert(type(d)=="t_INT" && !issquare(d));
  cf=contfrac(sqrt(d)); my(h=find_first(cf,2*a(0))-1); if(h%2, h*=2);
  my(d=digmat(a(0))); for(i=1, h-1, d*=digmat(a(i))); d[,1]~
};

fundpari(d)={
  assert(type(d)=="t_INT" && !issquare(d));
  my(u=quadunit(4*d)); if(norm(u)<0, u*=u); [real(u), imag(u)];
}