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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
This commit is contained in:
Sylvain Munaut 2020-05-14 03:02:26 +07:00 committed by fixeria
parent 534f0f402b
commit 63bee45411
3 changed files with 58 additions and 0 deletions
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4
include/osmocom/gsm/gsm0502.h
View File

@ -47,3 +47,7 @@ enum gsm0502_fn_remap_channel {
};
uint32_t gsm0502_fn_remap(uint32_t fn, enum gsm0502_fn_remap_channel channel);
uint16_t gsm0502_hop_seq_gen(const struct gsm_time *t,
uint8_t hsn, uint8_t maio,
size_t n, const uint16_t *ma);

53
src/gsm/gsm0502.c
View File

@ -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 @@ uint32_t gsm0502_fn_remap(uint32_t fn, enum gsm0502_fn_remap_channel channel)
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;
}

1
src/gsm/libosmogsm.map
View File

@ -110,6 +110,7 @@ gsm0480_gen_reject;
gsm0502_calc_paging_group;
gsm0502_fn_remap;
gsm0502_hop_seq_gen;
gsm0503_xcch;
gsm0503_rach;