[hackers] [libzahl] Fix another error in the solution for Powers of the golden ratio || Mattias Andrée

[git]

commit a5ae82e67f914d9339ac22e0c2df9fe9b79b0f57
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Mon Jul 25 17:03:54 2016 +0200
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Mon Jul 25 17:03:54 2016 +0200

    Fix another error in the solution for Powers of the golden ratio
    
    Signed-off-by: Mattias Andrée <maand...@kth.se>

diff --git a/doc/exercises.tex b/doc/exercises.tex
index 93f77e4..160067d 100644
--- a/doc/exercises.tex
+++ b/doc/exercises.tex
@@ -488,7 +488,7 @@ the set of pseudoprimes.
 \item \textbf{Powers of the golden ratio}
 
 This was an information gathering exercise.
-For $n \ge 1$, $L_n = [\varphi^n]$, where
+For $n \ge 2$, $L_n = [\varphi^n]$, where
 $L_n$ is the $n^\text{th}$ Lucas number.
 
 \( \displaystyle{
@@ -505,12 +505,14 @@ but for efficiency and briefness, we will use
 
 \vspace{-1em}
 \begin{alltt}
-void golden_pow(z_t r, z_t p)
+void golden_pow(z_t r, z_t n)
 \{
-    if (zsignum(p) <= 0)
-        zsetu(r, zcmpi(p, -1) >= 0);
+    if (zsignum(n) <= 0)
+        zsetu(r, zcmpi(n, -1) >= 0);
+    else if (!zcmpu(n, 1))
+        zsetu(r, 2);
     else
-        lucas(r, p);
+        lucas(r, n);
 \}
 \end{alltt}