1 files changed, 16 insertions, 0 deletions
diff --git a/src/tsfn.cpp b/src/tsfn.cpp
new file mode 100644
index 00000000..ea3b896d
--- /dev/null
+++ b/src/tsfn.cpp
@@ -0,0 +1,16 @@
+/* determine small t */
+#include <math.h>
+#include "projects.h"
+
+double pj_tsfn(double phi, double sinphi, double e) {
+    double denominator;
+    sinphi *= e;
+
+    /* avoid zero division, fail gracefully */
+    denominator = 1.0 + sinphi;
+    if (denominator == 0.0)
+        return HUGE_VAL;
+
+    return (tan (.5 * (M_HALFPI - phi)) /
+            pow((1. - sinphi) / (denominator), .5 * e));
+}