Data commit

Task/Jacobi-symbol/Erlang/jacobi-symbol.erl

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+jacobi(_, N) when N =< 0 -> jacobi_domain_error;
+jacobi(_, N) when (N band 1) =:= 0 -> jacobi_domain_error;
+jacobi(A, N) when A < 0 ->
+    J2 = ja(-A, N),
+    case N band 3 of
+        1 -> J2;
+        3 -> -J2
+    end;
+jacobi(A, N) -> ja(A, N).
+
+ja(0, _) -> 0;
+ja(1, _) -> 1;
+ja(A, N) when A >= N -> ja(A rem N, N);
+ja(A, N) when (A band 1) =:= 0 -> % A is even
+    J2 = ja(A bsr 1, N),
+    case N band 7 of
+        1 -> J2;
+        3 -> -J2;
+        5 -> -J2;
+        7 -> J2
+    end;
+ja(A, N) ->    % if we get here, A is odd, so we can flip it.
+    J2 = ja(N, A),
+    case (A band 3 =:= 3) and (N band 3 =:= 3) of
+        true  -> -J2;
+        false -> J2
+    end.