From 385a5a6cbcab9001633efd700b2ffdeaf1aaaf6d Mon Sep 17 00:00:00 2001
From: Alex Schmidt <alex@treefish.org>
Date: Tue, 26 Jun 2012 21:06:08 +1000
Subject: [PATCH] ...

---
 neigh.cpp | 28 ++++++++++++++++++++++++++++
 neigh.h   | 18 ++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 neigh.cpp
 create mode 100644 neigh.h

diff --git a/neigh.cpp b/neigh.cpp
new file mode 100644
index 0000000..a25d1e7
--- /dev/null
+++ b/neigh.cpp
@@ -0,0 +1,28 @@
+#include "neigh.h"
+
+neigh::neigh(const int& dimension, const int& length)
+{
+  nfield = new int[ipow(dimension,length)*2*dimension];
+
+  for (int ipos = 0; ipos < ipow(length,dimension); ipos++)
+    {
+      for (int idir = 0; idir < 2*dimension; idir++)
+	{
+	  if ( idir < dimension ) //pos direction
+	    {
+	      if ( ( ipos/ipow(length,idir%dimension) ) % length == length-1 )
+		nfield[ipos*2*dimension + idir] = ipos - ipow(length,idir%dimension)*(length-1);
+	      else
+		nfield[ipos*2*dimension + idir] = ipos + ipow(length,idir%dimension);
+	    }
+	  else //negative dir
+	    {
+	      if ( ( ipos/ipow(length,idir%dimension) ) % length == 0 )
+		nfield[ipos*2*dimension + idir] = ipos + ipow(length,idir%dimension)*(length-1);
+	      else
+		nfield[ipos*2*dimension + idir] = ipos - ipow(length,idir%dimension);
+	    }
+	  
+	}
+    }
+}
diff --git a/neigh.h b/neigh.h
new file mode 100644
index 0000000..73ffe62
--- /dev/null
+++ b/neigh.h
@@ -0,0 +1,18 @@
+#ifndef NEIGH_H
+#define NEIGH_H
+
+class neigh
+{
+ private:
+  int *nfield;
+  static int ipow(const int& x, const int& p){
+    if (p == 0) return 1;
+    if (p == 1) return x;
+    return x * ipow(x, p-1);
+  }
+ public:
+  neigh(const int& length, const int& dimension);
+  int& operator[] (int i) {return nfield[i];}
+};
+
+#endif
-- 
2.39.5