gsm0502: add TDMA frame number constants and modular arithmetic
These TDMA constatns and modular arithmetic operations are used in
a number of osmo-* projects, so it makes sense to have them all
in a single header file, with minimalistic documentation.
Change-Id: Ic291fd3644f34964374227a191c7045d79d77e0d
diff --git a/include/osmocom/gsm/gsm0502.h b/include/osmocom/gsm/gsm0502.h
index cb993dc..1be2cc3 100644
--- a/include/osmocom/gsm/gsm0502.h
+++ b/include/osmocom/gsm/gsm0502.h
@@ -7,6 +7,30 @@
#include <osmocom/gsm/protocol/gsm_04_08.h>
#include <osmocom/gsm/protocol/gsm_08_58.h>
+/* 4.3.3 TDMA frame number : constants and modular arithmetic */
+#define GSM_TDMA_FN_DURATION_nS 4615384 /* in 1e−9 seconds (approx) */
+#define GSM_TDMA_FN_DURATION_uS 4615 /* in 1e-6 seconds (approx) */
+
+#define GSM_TDMA_SUPERFRAME (26 * 51)
+#define GSM_TDMA_HYPERFRAME (2048 * GSM_TDMA_SUPERFRAME)
+
+/*! Return the sum of two specified TDMA frame numbers (summation) */
+#define GSM_TDMA_FN_SUM(a, b) \
+ ((a + b) % GSM_TDMA_HYPERFRAME)
+/*! Return the difference of two specified TDMA frame numbers (subtraction) */
+#define GSM_TDMA_FN_SUB(a, b) \
+ ((a + GSM_TDMA_HYPERFRAME - b) % GSM_TDMA_HYPERFRAME)
+/*! Return the *minimum* difference of two specified TDMA frame numbers (distance) */
+#define GSM_TDMA_FN_DIFF(a, b) \
+ OSMO_MIN(GSM_TDMA_FN_SUB(a, b), GSM_TDMA_FN_SUB(b, a))
+
+/*! Increment the given TDMA frame number by 1 and return the result (like ++fn) */
+#define GSM_TDMA_FN_INC(fn) \
+ ((fn) = GSM_TDMA_FN_SUM((fn), 1))
+/*! Decrement the given TDMA frame number by 1 and return the result (like --fn) */
+#define GSM_TDMA_FN_DEC(fn) \
+ ((fn) = GSM_TDMA_FN_SUB((fn), 1))
+
/* Table 5 Clause 7 TS 05.02 */
static inline unsigned int
gsm0502_get_n_pag_blocks(struct gsm48_control_channel_descr *chan_desc)