1 files changed, 30 insertions, 0 deletions
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