diff --git a/include/grgsm/misc_utils/fn_time.h b/include/grgsm/misc_utils/fn_time.h
index 560ee4a..b26c21b 100644
--- a/include/grgsm/misc_utils/fn_time.h
+++ b/include/grgsm/misc_utils/fn_time.h
@@ -1,6 +1,7 @@
 /* -*- c++ -*- */
 /* @file
  * @author Piotr Krysik <ptrkrysik@gmail.com>
+ * @author Vadim Yanitskiy <axilirator@gmail.com>
  * @section LICENSE
  * 
  * Gr-gsm is free software; you can redistribute it and/or modify
@@ -24,8 +25,9 @@
 #ifndef INCLUDED_GRGSM_FN_TIME_H
 #define INCLUDED_GRGSM_FN_TIME_H
 
+#include <grgsm/api.h>
 #include <stdint.h>
-#include <grgsm/misc_utils/time_spec.h>
+#include <utility>
 
 namespace gr {
   namespace gsm {
@@ -41,10 +43,12 @@
      *                   frame numbers
      * @return           difference between fn_ref and fn
      */
-    time_spec_t fn_time_delta2(uint32_t fn_ref, time_spec_t time_ref, uint32_t fn_x, 
-      time_spec_t time_hint, uint32_t ts_num, uint32_t ts_ref);
+     typedef std::pair<unsigned long long, double> time_format;
+     
+    GRGSM_API time_format fn_time_delta_cpp(uint32_t fn_ref, time_format time_ref, uint32_t fn_x,
+      time_format time_hint, uint32_t ts_num, uint32_t ts_ref);
 
-  } // namespace grgsm
+  } // namespace gsm
 } // namespace gr
 
 #endif /* INCLUDED_GRGSM_FN_TIME_H */
diff --git a/lib/misc_utils/fn_time.cc b/lib/misc_utils/fn_time.cc
index 25c8e65..2773f33 100644
--- a/lib/misc_utils/fn_time.cc
+++ b/lib/misc_utils/fn_time.cc
@@ -22,35 +22,38 @@
  */
 
 #include <grgsm/misc_utils/fn_time.h>
+#include <grgsm/misc_utils/time_spec.h>
 #include <math.h>
 
-#define GSM_HYPER_FRAME 26 * 51 * 2048
-#define GSM_SYM_RATE 13.0e6 / 48.0
+#define GSM_HYPER_FRAME (26 * 51 * 2048)
+#define GSM_SYM_RATE (13.0e6 / 48.0)
 
-#define GSM_TS_PERIOD 156.25 / GSM_SYM_RATE
-#define GSM_FN_PERIOD 8 * GSM_TS_PERIOD
+#define GSM_TS_PERIOD (156.25 / GSM_SYM_RATE)
+#define GSM_FN_PERIOD (8 * GSM_TS_PERIOD)
 
 namespace gr {
   namespace gsm {
-  	/**
-  	 * Computes difference between two frame numbers modulo
-  	 * GSM_HYPER_FRAME / 2. The result is correct if difference
-  	 * between the frame numbers is not bigger than GSM_HYPER_FRAME / 2.
-  	 * @param  fn1 first frame number
-  	 * @param  fn2 second frame number
-  	 * @return     computed difference
-  	 */
-    static uint32_t fnmod_delta(uint32_t fn1, uint32_t fn2)
+    /**
+     * Computes difference between two frame numbers modulo
+     * GSM_HYPER_FRAME / 2. The result is correct if difference
+     * between the frame numbers is not bigger than GSM_HYPER_FRAME / 2.
+     * @param  fn1 first frame number
+     * @param  fn2 second frame number
+     * @return     computed difference
+     */
+    static int fnmod_delta(uint32_t fn1, uint32_t fn2)
     {
-      uint32_t delta, h2;
+      int delta, h2;
 
       delta = (fn1 % GSM_HYPER_FRAME) - (fn2 % GSM_HYPER_FRAME);
+
       h2 = GSM_HYPER_FRAME / 2;
 
-      if (delta >= h2)
-      	delta -= GSM_HYPER_FRAME;
-      else
-      	delta += GSM_HYPER_FRAME;
+      if (delta >= h2) {
+        delta -= GSM_HYPER_FRAME;
+      } else if(delta < -h2) {
+        delta += GSM_HYPER_FRAME;
+      }
 
       return delta;
     }
@@ -59,7 +62,6 @@
       time_spec_t time_diff_hint)
     {
       int frames_diff, fn_delta;
-
       frames_diff = int(round(time_diff_hint.get_real_secs() / GSM_FN_PERIOD));
       fn_delta = fnmod_delta(fn, fn_ref + frames_diff) + frames_diff;
 
@@ -77,27 +79,16 @@
      *                   frame numbers
      * @return           difference between fn_ref and fn
      */
-    time_spec_t fn_time_delta2(uint32_t fn_ref, time_spec_t time_ref, uint32_t fn_x, 
-      time_spec_t time_hint, uint32_t ts_num, uint32_t ts_ref)
+    time_format fn_time_delta_cpp(uint32_t fn_ref, time_format time_ref, uint32_t fn_x, 
+      time_format time_hint, uint32_t ts_num, uint32_t ts_ref)
     {
-			time_spec_t time_diff_hint = time_hint - time_ref;
-      uint32_t fn_delta = fn_time_diff_delta(fn_x,fn_ref, time_diff_hint);
-      time_spec_t time_x_precise = fn_delta * GSM_FN_PERIOD
-        + time_ref + (ts_num - ts_ref) * GSM_TS_PERIOD;
-      
-      return time_x_precise;
+      time_spec_t time_diff_hint = time_spec_t(time_hint.first, time_hint.second) - time_spec_t(time_ref.first, time_ref.second);
+      int fn_delta = fn_time_diff_delta(fn_x, fn_ref, time_diff_hint);
+      time_spec_t time_x_precise = fn_delta * GSM_FN_PERIOD + time_spec_t(time_ref.first, time_ref.second) + (static_cast<int>(ts_num) - static_cast<int>(ts_ref)) * GSM_TS_PERIOD;
+
+      return time_format(time_x_precise.get_full_secs(), time_x_precise.get_frac_secs());
     }
-/*
-    def fn_time_delta(fn_ref, time_ref, fn_x, time_hint=None, ts_num=0, ts_ref=0):
-      if time_hint is None:
-          time_hint = time_ref
-          
-      time_diff_hint = time_hint-time_ref
-      fn_delta = fn_time_diff_delta(fn_x,fn_ref, time_diff_hint)
-      time_x_precise = fn_delta*__frame_period+time_ref+(ts_num-ts_ref)*__ts_period
-      
-      return fn_delta, time_x_precise
-*/
+
   } /* namespace gsm */
 } /* namespace gr */
 
diff --git a/python/misc_utils/fn_time.py b/python/misc_utils/fn_time.py
index cf03681..96314b8 100644
--- a/python/misc_utils/fn_time.py
+++ b/python/misc_utils/fn_time.py
@@ -22,6 +22,7 @@
 # 
 from math import floor, ceil
 from random import uniform
+from grgsm import fn_time_delta_cpp
 
 __hyper_frame = 26*51*2048
 __symb_rate = 13.0e6/48.0
@@ -37,7 +38,7 @@
 def fnmod_delta(fn1, fn2):
     h2 = __hyper_frame/2
     delta = (fn1%__hyper_frame)-(fn2%__hyper_frame)
-  
+    
     if delta >= h2:
         delta = delta - __hyper_frame
     elif delta < -h2:
@@ -49,7 +50,7 @@
     frames_diff = int(round(time_diff_hint/__frame_period))
     fn_ref_hint = (fn_ref + frames_diff)
     fn_delta = fnmod_delta(fn_x,fn_ref_hint)+frames_diff
-    
+
     return fn_delta
 
 #fn_time_delta computes difference between reference frame number and a second frame number. It also computes timestamp of the second frame number. The full list of parameters is following:
@@ -73,16 +74,19 @@
 if __name__ == "__main__":
     fn1 = 10000
     ts_ref = 4
-    time1 = 10
-    for fn2 in xrange(__hyper_frame/2+fn1-10,__hyper_frame/2*10+fn1+10,10):
+    time1 = 10.5
+    for fn2 in xrange(__hyper_frame/2+fn1-10,__hyper_frame/2*10+fn1+100,10):
         ts_x = int(uniform(0,8))
-        time2 = time1 + (fn2-fn1)*__frame_period + (ts_ref-ts_x)*__ts_period
+        time2 = time1 + (fn2-fn1)*__frame_period + (ts_x-ts_ref)*__ts_period
         error = uniform(-6200,6200)
         time2_err = time2+error
         fn_delta, time2_precise = fn_time_delta(fn1, time1, fn2, time2_err, ts_x, ts_ref)
+        time2_precise_cpp = fn_time_delta_cpp(fn1, (int(time1),time1-int(time1)), fn2, (int(time2_err),time2_err-int(time2_err)), ts_x, ts_ref)
         if fn_delta != fn2-fn1:
             print "bad fn:", fn2, error#, 'fn_delta:'+str(fn_delta), time2, error, frames_diff_h4, (time2-time1)/(__hyper_frame*__frame_period), time_diff_hint_h4_prev, time_diff_hint
-        time_diff_hint = time2 - time2_precise
-        if time_diff_hint > 0.0001:
-            print "bad time diff"
+#        time_diff_hint = time2 - time2_precise
+        time_diff_hint = time2_precise_cpp[0]+time2_precise_cpp[1] - time2_precise
 
+        if abs(time_diff_hint) > 0.0001:
+            print "time2_precise_cpp",time2_precise_cpp," time2_precise",time2_precise," time_ref",time1," time_hint",time2_err
+            print ""
diff --git a/swig/grgsm_swig.i b/swig/grgsm_swig.i
index d5132dc..56e988d 100644
--- a/swig/grgsm_swig.i
+++ b/swig/grgsm_swig.i
@@ -23,6 +23,9 @@
 
 #define GRGSM_API
 
+%include <std_pair.i>
+%template(pairud) std::pair<unsigned long long,double>;
+
 %include "gnuradio.i"			// the common stuff
 
 //load generated python docstrings
@@ -65,7 +68,7 @@
 #include "grgsm/misc_utils/msg_to_tag.h"
 #include "grgsm/misc_utils/controlled_fractional_resampler_cc.h"
 #include "grgsm/trx_interface/trx.h"
-#include "grgsm/misc_utils/time_spec.h"
+//#include "grgsm/misc_utils/time_spec.h"
 #include "grgsm/misc_utils/fn_time.h"
 %}
 
@@ -149,4 +152,4 @@
 %include "grgsm/trx_interface/trx.h"
 GR_SWIG_BLOCK_MAGIC2(grgsm, trx);
 //%include "grgsm/misc_utils/time_spec.h"
-//%include "grgsm/misc_utils/fn_time.h"
+%include "grgsm/misc_utils/fn_time.h"