gsm: add gsm0502_fn_compare() for comparing TDMA FNs
We need this function in:
* osmocom-bb.git for trxcon and l1gprs,
* osmo-pcu.git replacing fn_cmp().
Change-Id: I9590f2e836fc48650decf1564b6ab46306c4fe2d
Related: OS#5500
diff --git a/include/osmocom/gsm/gsm0502.h b/include/osmocom/gsm/gsm0502.h
index ffd6e20..6624e70 100644
--- a/include/osmocom/gsm/gsm0502.h
+++ b/include/osmocom/gsm/gsm0502.h
@@ -64,6 +64,25 @@
#define GSM_NBITS_AB_GMSK_TAIL GSM_NBITS_NB_GMSK_TAIL
#define GSM_NBITS_AB_GMSK_BURST GSM_NBITS_NB_GMSK_BURST
+/*! Compare the given TDMA FNs, taking the wrapping into account.
+ * \param[in] fn1 First TDMA Fn value to compare.
+ * \param[in] fn2 Second TDMA Fn value to compare.
+ * \returns similarly to memcmp(), -1 if fn1 goes before fn2;
+ * 0 if fn1 equals fn2;
+ * 1 if fn1 goes after fn2. */
+static inline int gsm0502_fn_compare(uint32_t fn1, uint32_t fn2)
+{
+ const uint32_t thresh = GSM_TDMA_HYPERFRAME / 2;
+
+ if (fn1 == fn2)
+ return 0;
+ if ((fn1 < fn2 && (fn2 - fn1) < thresh) ||
+ (fn1 > fn2 && (fn1 - fn2) > thresh))
+ return -1;
+
+ return 1;
+}
+
/* Table 5 Clause 7 TS 05.02 */
static inline unsigned int
gsm0502_get_n_pag_blocks(const struct gsm48_control_channel_descr *chan_desc)