From 0980e48d8d4db20da92684dea42de871b153cd7e Mon Sep 17 00:00:00 2001
From: Yury Melnichek <melnichek@gmail.com>
Date: Sat, 15 Jan 2011 23:50:13 +0200
Subject: [PATCH] Add NextModN(), PrevModN(), NextIterInCycle(),
 PrevIterInCycle().

---
 base/math.hpp    | 10 ++++++++++
 base/stl_add.hpp | 15 +++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/base/math.hpp b/base/math.hpp
index 096fe94f1c..7e98ed501e 100644
--- a/base/math.hpp
+++ b/base/math.hpp
@@ -105,4 +105,14 @@ template <typename T> inline T PowUint(T x, uint64_t n)
   return res;
 }
 
+template <typename T> inline T NextModN(T x, T n)
+{
+  return x + 1 == n ? 0 : x + 1;
+}
+
+template <typename T> inline T PrevModN(T x, T n)
+{
+  return x == 0 ? n - 1 : x - 1;
+}
+
 }
diff --git a/base/stl_add.hpp b/base/stl_add.hpp
index a17dd0e023..9f9d5437b9 100644
--- a/base/stl_add.hpp
+++ b/base/stl_add.hpp
@@ -93,3 +93,18 @@ struct NoopFunctor
     UNUSED_VALUE(value);
   }
 };
+
+template <typename IterT> IterT NextIterInCycle(IterT it, IterT beg, IterT end)
+{
+  if (++it == end)
+    return beg;
+  return it;
+}
+
+template <typename IterT> IterT PrevIterInCycle(IterT it, IterT beg, IterT end)
+{
+  if (it == beg)
+    it = end;
+  return --it;
+}
+