libosmogsm: import hopping sequence generation code
This implementation is taken from OsmocomBB, in particular from:
target/firmware/layer1/rfch.c
Change return type to uint16_t, because neither ARFCN, nor MAI
can be negative. Add prefix 'gsm0502_' to the function's name.
Change-Id: I8aba1578cc9d1bd89d4f5d33a6e8fedc8bea789a
Related: OS#4546
diff --git a/src/gsm/gsm0502.c b/src/gsm/gsm0502.c
index 5c5aa12..7ab6343 100644
--- a/src/gsm/gsm0502.c
+++ b/src/gsm/gsm0502.c
@@ -2,6 +2,8 @@
* Paging helper code */
/*
* (C) 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
+ * (C) 2010 by Sylvain Munaut <tnt@246tNt.com>
+ *
* All Rights Reserved
*
* SPDX-License-Identifier: GPL-2.0+
@@ -201,3 +203,54 @@
return fn_map;
}
+
+/* Magic numbers (RNTABLE) for pseudo-random hopping sequence generation. */
+static const uint8_t rn_table[114] = {
+ 48, 98, 63, 1, 36, 95, 78, 102, 94, 73,
+ 0, 64, 25, 81, 76, 59, 124, 23, 104, 100,
+ 101, 47, 118, 85, 18, 56, 96, 86, 54, 2,
+ 80, 34, 127, 13, 6, 89, 57, 103, 12, 74,
+ 55, 111, 75, 38, 109, 71, 112, 29, 11, 88,
+ 87, 19, 3, 68, 110, 26, 33, 31, 8, 45,
+ 82, 58, 40, 107, 32, 5, 106, 92, 62, 67,
+ 77, 108, 122, 37, 60, 66, 121, 42, 51, 126,
+ 117, 114, 4, 90, 43, 52, 53, 113, 120, 72,
+ 16, 49, 7, 79, 119, 61, 22, 84, 9, 97,
+ 91, 15, 21, 24, 46, 39, 93, 105, 65, 70,
+ 125, 99, 17, 123,
+};
+
+/*! Hopping sequence generation as per 3GPP TS 45.002, section 6.2.3. */
+uint16_t gsm0502_hop_seq_gen(const struct gsm_time *t,
+ uint8_t hsn, uint8_t maio,
+ size_t n, const uint16_t *ma)
+{
+ unsigned int mai;
+
+ if (hsn == 0) {
+ /* cyclic hopping */
+ mai = (t->fn + maio) % n;
+ } else {
+ /* pseudo random hopping */
+ int m, mp, tp, s, pnm;
+
+ pnm = (n >> 0) | (n >> 1)
+ | (n >> 2) | (n >> 3)
+ | (n >> 4) | (n >> 5)
+ | (n >> 6);
+
+ m = t->t2 + rn_table[(hsn ^ (t->t1 & 63)) + t->t3];
+ mp = m & pnm;
+
+ if (mp < n)
+ s = mp;
+ else {
+ tp = t->t3 & pnm;
+ s = (mp + tp) % n;
+ }
+
+ mai = (s + maio) % n;
+ }
+
+ return ma ? ma[mai] : mai;
+}