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From: <git_AT_suckless.org>
Date: Mon, 25 Jul 2016 16:57:13 +0200 (CEST)

commit 60dd5110e21d1aedc047f2033af74330df552e40
Author: Mattias Andrée <maandree_AT_kth.se>
AuthorDate: Mon Jul 25 16:15:08 2016 +0200
Commit: Mattias Andrée <maandree_AT_kth.se>
CommitDate: Mon Jul 25 16:15:08 2016 +0200

Manual: How to calculate the Jacobi symbol

Signed-off-by: Mattias Andrée <maandree_AT_kth.se>

diff --git a/doc/not-implemented.tex b/doc/not-implemented.tex
index 27a03d5..6cff52e 100644
--- a/doc/not-implemented.tex
+++ b/doc/not-implemented.tex
_AT_@ -141,10 +141,11 @@ TODO
\left ( \frac{a}{p} \right ) \in \{-1,~0,~1\},~
p \in \textbf{P},~ p > 2
}\)
+\vspace{1em}

\noindent
-That is, unless $\displaystyle{a^{\frac{p - 1}{2}} ~\text{Mod}~ p \le 1}$,
-$\displaystyle{a^{\frac{p - 1}{2}} ~\text{Mod}~ p = p - 1}$, so
+That is, unless $\displaystyle{a^{\frac{p - 1}{2}} \mod p \le 1}$,
+$\displaystyle{a^{\frac{p - 1}{2}} \mod p = p - 1}$, so
$\displaystyle{\left ( \frac{a}{p} \right ) = -1}$.

It should be noted that
_AT_@ -158,7 +159,46 @@ so a compressed lookup table can be used for small $p$.
\subsection{Jacobi symbol}
\label{sec:Jacobi symbol}

-TODO
+$$\displaystyle{ + \left ( \frac{a}{n} \right ) = + \prod_k \left ( \frac{a}{p_k} \right )^{n_k}, +}$$
+where $n$ = $\displaystyle{\prod_k p_k^{n_k}}$, and $p_k \in \textbf{P}$.
+\vspace{1em}
+
+Like the Legendre symbol, the Jacobi symbol is $n$-period over $a$.
+If $n$, is prime, the Jacobi symbol is the Legendre symbol, but
+the Jacobi symbol is defined for all odd numbers $n$, where the
+Legendre symbol is defined only for odd primes $n$.
+
+Use the following algorithm to calculate the Jacobi symbol:
+
+\vspace{1em}
+\hspace{-2.8ex}
+\begin{minipage}{\linewidth}
+\begin{algorithmic}
+ \STATE $a \gets a \mod n$
+ \STATE $r \gets \mbox{lsb}~ a$
+ \STATE $a \gets a \cdot 2^{-r}$
+ \STATE $$\displaystyle{ + r \gets \left \lbrace \begin{array}{rl} + 1 & + \text{if}~ n \equiv 1, 7 ~(\text{Mod}~ 8) + ~\text{or}~ r \equiv 0 ~(\text{Mod}~ 2) \\ + -1 & \text{otherwise} \\ + \end{array} \right . + }$$
+ \IF{$a = 1$}
+ \RETURN $r$
+ \ELSIF{$\gcd(a, n) \neq 1$}
+ \RETURN $0$
+ \ENDIF
+ \STATE $(a, n) = (n, a)$
+ \STATE \textbf{start over}
+\end{algorithmic}
+\end{minipage}
+\vspace{1em}
+

\subsection{Kronecker symbol}
Received on Mon Jul 25 2016 - 16:57:13 CEST

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