From efe0d24fa7dbca47825638a52f51977456153bd0 Mon Sep 17 00:00:00 2001
From: "philblunsom@gmail.com"
 <philblunsom@gmail.com@ec762483-ff6d-05da-a07a-a48fb63a330f>
Date: Tue, 22 Jun 2010 20:34:00 +0000
Subject: Initial ci of gi dir

git-svn-id: https://ws10smt.googlecode.com/svn/trunk@5 ec762483-ff6d-05da-a07a-a48fb63a330f
---
 gi/pyp-topics/src/log_add.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 gi/pyp-topics/src/log_add.h

(limited to 'gi/pyp-topics/src/log_add.h')

diff --git a/gi/pyp-topics/src/log_add.h b/gi/pyp-topics/src/log_add.h
new file mode 100644
index 00000000..e0620c5a
--- /dev/null
+++ b/gi/pyp-topics/src/log_add.h
@@ -0,0 +1,30 @@
+#ifndef log_add_hh
+#define log_add_hh
+
+#include <limits>
+#include <iostream>
+#include <cassert>
+#include <cmath>
+
+template <typename T>
+struct Log
+{
+    static T zero() { return -std::numeric_limits<T>::infinity(); } 
+
+    static T add(T l1, T l2)
+    {
+        if (l1 == zero()) return l2;
+        if (l1 > l2) 
+            return l1 + std::log(1 + exp(l2 - l1));
+        else
+            return l2 + std::log(1 + exp(l1 - l2));
+    }
+
+    static T subtract(T l1, T l2)
+    {
+        //std::assert(l1 >= l2);
+        return l1 + log(1 - exp(l2 - l1));
+    }
+};
+
+#endif
-- 
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