From fdf8b7b1beeb0cda262c5fb060a933aa7edb5e9a Mon Sep 17 00:00:00 2001 From: Stefan Sperling Date: Fri, 27 Jul 2018 12:19:15 +0200 Subject: port arfcn range encode support from osmo-bsc As part of fixing issue OS#3075, we want to migrate support for encoding system information from osmo-bsc to libosmocore. This change ports one of the prerequisites for doing so: osmo-bsc code for range-encoding ARFCNs, including tests. An osmo_gsm48_ prefix has been prepended to public symbols in order to avoid clashes with existing symbols in osmo-bsc code. Change-Id: Ia220764fba451be5e975ae7c5eefb1a25ac2bf2c Related: OS#3075 --- src/gsm/Makefile.am | 3 +- src/gsm/gsm48_arfcn_range_encode.c | 321 +++++++++++++++++++++++++++++++++++++ src/gsm/libosmogsm.map | 9 ++ 3 files changed, 332 insertions(+), 1 deletion(-) create mode 100644 src/gsm/gsm48_arfcn_range_encode.c (limited to 'src/gsm') diff --git a/src/gsm/Makefile.am b/src/gsm/Makefile.am index 3d2c5606..c4b5fce3 100644 --- a/src/gsm/Makefile.am +++ b/src/gsm/Makefile.am @@ -21,7 +21,8 @@ lib_LTLIBRARIES = libosmogsm.la BUILT_SOURCES = gsm0503_conv.c libgsmint_la_SOURCES = a5.c rxlev_stat.c tlv_parser.c comp128.c comp128v23.c \ - gsm_utils.c rsl.c gsm48.c gsm48_ie.c gsm0808.c sysinfo.c \ + gsm_utils.c rsl.c gsm48.c gsm48_arfcn_range_encode.c \ + gsm48_ie.c gsm0808.c sysinfo.c \ gprs_cipher_core.c gprs_rlc.c gsm0480.c abis_nm.c gsm0502.c \ gsm0411_utils.c gsm0411_smc.c gsm0411_smr.c gsm0414.c \ lapd_core.c lapdm.c kasumi.c gsm29205.c gsm_04_08_gprs.c \ diff --git a/src/gsm/gsm48_arfcn_range_encode.c b/src/gsm/gsm48_arfcn_range_encode.c new file mode 100644 index 00000000..6423a9a8 --- /dev/null +++ b/src/gsm/gsm48_arfcn_range_encode.c @@ -0,0 +1,321 @@ +/* gsm 04.08 system information (si) encoding and decoding + * 3gpp ts 04.08 version 7.21.0 release 1998 / etsi ts 100 940 v7.21.0 */ + +/* + * (C) 2012 Holger Hans Peter Freyther + * (C) 2012 by On-Waves + * All Rights Reserved + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Affero General Public License as published by + * the Free Software Foundation; either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Affero General Public License for more details. + * + * You should have received a copy of the GNU Affero General Public License + * along with this program. If not, see . + */ + +#include +#include + +#include + +#include + +static inline int greatest_power_of_2_lesser_or_equal_to(int index) +{ + int power_of_2 = 1; + + do { + power_of_2 *= 2; + } while (power_of_2 <= index); + + /* now go back one step */ + return power_of_2 / 2; +} + +static inline int mod(int data, int range) +{ + int res = data % range; + while (res < 0) + res += range; + return res; +} + +/** + * Determine at which index to split the ARFCNs to create an + * equally size partition for the given range. Return -1 if + * no such partition exists. + */ +int osmo_gsm48_range_enc_find_index(enum osmo_gsm48_range range, const int *freqs, const int size) +{ + int i, j, n; + + const int RANGE_DELTA = (range - 1) / 2; + + for (i = 0; i < size; ++i) { + n = 0; + for (j = 0; j < size; ++j) { + if (mod(freqs[j] - freqs[i], range) <= RANGE_DELTA) + n += 1; + } + + if (n - 1 == (size - 1) / 2) + return i; + } + + return -1; +} + +/* Worker for range_enc_arfcns(), do not call directly. */ +static int _range_enc_arfcns(enum osmo_gsm48_range range, + const int *arfcns, int size, int *out, + const int index) +{ + int split_at; + int i; + + /* + * The below is a GNU extension and we can remove it when + * we move to a quicksort like in-situ swap with the pivot. + */ + int arfcns_left[size / 2]; + int arfcns_right[size / 2]; + int l_size; + int r_size; + int l_origin; + int r_origin; + + /* Now do the processing */ + split_at = osmo_gsm48_range_enc_find_index(range, arfcns, size); + if (split_at < 0) + return -EINVAL; + + /* we now know where to split */ + out[index] = 1 + arfcns[split_at]; + + /* calculate the work that needs to be done for the leafs */ + l_origin = mod(arfcns[split_at] + ((range - 1) / 2) + 1, range); + r_origin = mod(arfcns[split_at] + 1, range); + for (i = 0, l_size = 0, r_size = 0; i < size; ++i) { + if (mod(arfcns[i] - l_origin, range) < range / 2) + arfcns_left[l_size++] = mod(arfcns[i] - l_origin, range); + if (mod(arfcns[i] - r_origin, range) < range / 2) + arfcns_right[r_size++] = mod(arfcns[i] - r_origin, range); + } + + /* + * Now recurse and we need to make this iterative... but as the + * tree is balanced the stack will not be too deep. + */ + if (l_size) + osmo_gsm48_range_enc_arfcns(range / 2, arfcns_left, l_size, + out, index + greatest_power_of_2_lesser_or_equal_to(index + 1)); + if (r_size) + osmo_gsm48_range_enc_arfcns((range - 1) / 2, arfcns_right, r_size, + out, index + (2 * greatest_power_of_2_lesser_or_equal_to(index + 1))); + return 0; +} + +/** + * Range encode the ARFCN list. + * \param range The range to use. + * \param arfcns The list of ARFCNs + * \param size The size of the list of ARFCNs + * \param out Place to store the W(i) output. + */ +int osmo_gsm48_range_enc_arfcns(enum osmo_gsm48_range range, + const int *arfcns, int size, int *out, + const int index) +{ + if (size <= 0) + return 0; + + if (size == 1) { + out[index] = 1 + arfcns[0]; + return 0; + } + + return _range_enc_arfcns(range, arfcns, size, out, index); +} + +/* + * The easiest is to use f0 == arfcns[0]. This means that under certain + * circumstances we can encode less ARFCNs than possible with an optimal f0. + * + * TODO: Solve the optimisation problem and pick f0 so that the max distance + * is the smallest. Taking into account the modulo operation. I think picking + * size/2 will be the optimal arfcn. + */ +/** + * This implements the range determination as described in GSM 04.08 J4. The + * result will be a base frequency f0 and the range to use. Note that for range + * 1024 encoding f0 always refers to ARFCN 0 even if it is not an element of + * the arfcns list. + * + * \param[in] arfcns The input frequencies, they must be sorted, lowest number first + * \param[in] size The length of the array + * \param[out] f0 The selected F0 base frequency. It might not be inside the list + */ +int osmo_gsm48_range_enc_determine_range(const int *arfcns, const int size, int *f0) +{ + int max = 0; + + /* + * Go for the easiest. And pick arfcns[0] == f0. + */ + max = arfcns[size - 1] - arfcns[0]; + *f0 = arfcns[0]; + + if (max < 128 && size <= 29) + return OSMO_GSM48_ARFCN_RANGE_128; + if (max < 256 && size <= 22) + return OSMO_GSM48_ARFCN_RANGE_256; + if (max < 512 && size <= 18) + return OSMO_GSM48_ARFCN_RANGE_512; + if (max < 1024 && size <= 17) { + *f0 = 0; + return OSMO_GSM48_ARFCN_RANGE_1024; + } + + return OSMO_GSM48_ARFCN_RANGE_INVALID; +} + +static void write_orig_arfcn(uint8_t *chan_list, int f0) +{ + chan_list[0] |= (f0 >> 9) & 1; + chan_list[1] = (f0 >> 1); + chan_list[2] = (f0 & 1) << 7; +} + +static void write_all_wn(uint8_t *chan_list, int bit_offs, + int *w, int w_size, int w1_len) +{ + int octet_offs = 0; /* offset into chan_list */ + int wk_len = w1_len; /* encoding size in bits of w[k] */ + int k; /* 1 based */ + int level = 0; /* tree level, top level = 0 */ + int lvl_left = 1; /* nodes per tree level */ + + /* W(2^i) to W(2^(i+1)-1) are on w1_len-i bits when present */ + + for (k = 1; k <= w_size; k++) { + int wk_left = wk_len; + + while (wk_left > 0) { + int cur_bits = 8 - bit_offs; + int cur_mask; + int wk_slice; + + if (cur_bits > wk_left) + cur_bits = wk_left; + + cur_mask = ((1 << cur_bits) - 1); + + /* advance */ + wk_left -= cur_bits; + bit_offs += cur_bits; + + /* right aligned wk data for current out octet */ + wk_slice = (w[k-1] >> wk_left) & cur_mask; + + /* cur_bits now contains the number of bits + * that are to be copied from wk to the chan_list. + * wk_left is set to the number of bits that must + * not yet be copied. + * bit_offs points after the bit area that is going to + * be overwritten: + * + * wk_left + * | + * v + * wk: WWWWWWWWWWW + * |||||<-- wk_slice, cur_bits=5 + * --WWWWW- + * ^ + * | + * bit_offs + */ + + chan_list[octet_offs] &= ~(cur_mask << (8 - bit_offs)); + chan_list[octet_offs] |= wk_slice << (8 - bit_offs); + + /* adjust output */ + if (bit_offs == 8) { + bit_offs = 0; + octet_offs += 1; + } + } + + /* adjust bit sizes */ + lvl_left -= 1; + if (!lvl_left) { + /* completed tree level, advance to next */ + level += 1; + lvl_left = 1 << level; + wk_len -= 1; + } + } +} + +int osmo_gsm48_range_enc_128(uint8_t *chan_list, int f0, int *w) +{ + chan_list[0] = 0x8C; + write_orig_arfcn(chan_list, f0); + + write_all_wn(&chan_list[2], 1, w, 28, 7); + return 0; +} + +int osmo_gsm48_range_enc_256(uint8_t *chan_list, int f0, int *w) +{ + chan_list[0] = 0x8A; + write_orig_arfcn(chan_list, f0); + + write_all_wn(&chan_list[2], 1, w, 21, 8); + return 0; +} + +int osmo_gsm48_range_enc_512(uint8_t *chan_list, int f0, int *w) +{ + chan_list[0] = 0x88; + write_orig_arfcn(chan_list, f0); + + write_all_wn(&chan_list[2], 1, w, 17, 9); + return 0; +} + +int osmo_gsm48_range_enc_1024(uint8_t *chan_list, int f0, int f0_included, int *w) +{ + chan_list[0] = 0x80 | (f0_included << 2); + + write_all_wn(&chan_list[0], 6, w, 16, 10); + return 0; +} + +int osmo_gsm48_range_enc_filter_arfcns(int *arfcns, const int size, const int f0, int *f0_included) +{ + int i, j = 0; + *f0_included = 0; + + for (i = 0; i < size; ++i) { + /* + * Appendix J.4 says the following: + * All frequencies except F(0), minus F(0) + 1. + * I assume we need to exclude it here. + */ + if (arfcns[i] == f0) { + *f0_included = 1; + continue; + } + + arfcns[j++] = mod(arfcns[i] - (f0 + 1), 1024); + } + + return j; +} diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map index cdcbcc98..922ac01f 100644 --- a/src/gsm/libosmogsm.map +++ b/src/gsm/libosmogsm.map @@ -518,6 +518,15 @@ osmo_apn_qualify_from_imsi; osmo_apn_to_str; osmo_apn_from_str; +osmo_gsm48_range_enc_determine_range; +osmo_gsm48_range_enc_arfcns; +osmo_gsm48_range_enc_find_index; +osmo_gsm48_range_enc_filter_arfcns; +osmo_gsm48_range_enc_128; +osmo_gsm48_range_enc_256; +osmo_gsm48_range_enc_512; +osmo_gsm48_range_enc_1024; + osmo_gsup_encode; osmo_gsup_decode; osmo_gsup_message_type_names; -- cgit v1.2.3