SW-546: When necessary add one spectral sample to the offset in spectral mode

RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc

@@ -469,6 +469,50 @@ namespace LOFAR
           << sliceNr << ", "
           << itsDumpInfo.itsSliceNr0);
 
+        /**
+         * Now check for even/odd seconds.  Why?  Because
+         * sampling frequency / (N * 1024) does not result in an integer without
+         * rest.  So one 1024 slice has to be moved to either ever odd or to
+         * every even second:
+         *
+         * slice #195312        slice #195313          slice #0
+         *      |                     |                    |
+         *      v                     v                    v
+         * 1024 ---------|--------- 1024 --------- |--------- 1024
+         *                            ^
+         *                            |
+         *              A new odd second begins here.
+         *
+         * slice #195312        slice #0               slice #1
+         *      |                     |                    |
+         *      v                     v                    v
+         * 1024 ---------|--------- 1024 --------- |--------- 1024
+         *               ^
+         *               |
+         *  A new even second begins here.
+         *
+         * What does this all mean?
+         * ------------------------
+         * If the time-stamp of the second of the first frame is even then
+         * the last frame had slice numbers up to #195313.
+         * The following slice numbers for the next second will only go up to
+         * #195312.
+         * - Check if the frame #0's second is even, then
+         * - check if the second of the current frame is odd.
+         * - Both yes:  means that we have to add one sample to the offset.
+         */
+        if((itsDumpInfo.itsTime0 % 2 == 0) && (frame.header.time % 2 == 1))
+        {
+            offset += 1;
+            LOG_INFO_STR("TBB:  Added one sample to the offset because t0 is "
+                "even and t_now is odd:  itsDumpInfo.itsTime0 = "
+                << itsDumpInfo.itsTime0
+                << ", frame.header.time = "
+                << frame.header.time
+                << ", offset = "
+                << offset);
+        }
+
         /**
          * Flag lost frame(s) (assumes no out-of-order).
          * Assumes all frames (except maybe the last) have the same nr of samples (fine).