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diff --git a/gi/posterior-regularisation/log_add.hh b/gi/posterior-regularisation/log_add.hh
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+#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