Add fsn lib to simplify frame/slot handling

Refactor existing code, and harmonize interface. Add a couple of tests.

Signed-off-by: Robert Schmidt <robert.schmidt@openairinterface.org>

common/utils/fsn.h

@@ -0,0 +1,36 @@
+/*
+ * SPDX-License-Identifier: LicenseRef-CSSL-1.0
+ */
+
+#ifndef FSN_H_
+#define FSN_H_
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/// helper type to encapsulate a frame/slot combination in a single type.
+typedef struct fsn {
+  uint16_t f; /// frame
+  uint16_t s; /// slot
+  uint8_t mu; /// numerology
+} fsn_t;
+
+/* \brief Add delta slots to fsn. Note that this depends also on the stored
+ * numerology inside fsn. */
+fsn_t fsn_add_delta(fsn_t fsn, uint32_t delta);
+
+/* \brief Get difference of slots for a and b.
+ * \note asserts if numerology not the same. */
+int fsn_get_diff(fsn_t a, fsn_t b);
+
+/* \brief Gets the larger of two fsns */
+fsn_t fsn_get_max(fsn_t a, fsn_t b);
+
+/* \brief Compare if both fsn_t's are equal */
+bool fsn_equal(fsn_t a, fsn_t b);
+
+/* \brief Determine if told is in the past of tnew. The threshold is 512
+ * frames. */
+bool fsn_in_the_past(fsn_t told, fsn_t tnew);
+
+#endif /* FSN_H_ */