It is based on https://developer.mbed.org/users/gregeric/code/Nucleo_Hello_Encoder/

Revision:
0:caf1d0bc4b90
Child:
2:4580c3869b7b
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rotary_encoder.cpp	Sat Feb 06 14:24:56 2016 +0000
@@ -0,0 +1,12 @@
+#include "mbed.h"
+#include "rotary_encoder.hpp"
+
+const size_t rotary_encoder::max_counts_ = 0xFFFF;
+
+rotary_encoder::rotary_encoder(size_t resolution) :
+        resolution_(resolution) {}
+rotary_encoder::~rotary_encoder() {}
+
+float rotary_encoder::get_revol_num() const {
+    return static_cast<float>(get_counts()) / resolution_;
+}