star function

1 files changed, 12 insertions, 0 deletions

diff --git a/utils/star.h b/utils/star.h
new file mode 100644
index 00000000..3295112c
--- /dev/null
+++ b/utils/star.h
@@ -0,0 +1,12 @@
+#ifndef _STAR_H_
+#define _STAR_H_
+
+template <typename T>
+T star(const T& x) {
+  if (!x) return T();
+  if (x > T(1)) return std::numeric_limits<T>::infinity();
+  if (x < -T(1)) return -std::numeric_limits<T>::infinity();
+  return T(1) / (T(1) - x);
+}
+
+#endif