Stefan Sperling | fdf8b7b | 2018-07-27 12:19:15 +0200 | [diff] [blame] | 1 | /* gsm 04.08 system information (si) encoding and decoding |
| 2 | * 3gpp ts 04.08 version 7.21.0 release 1998 / etsi ts 100 940 v7.21.0 */ |
| 3 | |
| 4 | /* |
| 5 | * (C) 2012 Holger Hans Peter Freyther |
| 6 | * (C) 2012 by On-Waves |
| 7 | * All Rights Reserved |
| 8 | * |
| 9 | * This program is free software; you can redistribute it and/or modify |
| 10 | * it under the terms of the GNU Affero General Public License as published by |
| 11 | * the Free Software Foundation; either version 3 of the License, or |
| 12 | * (at your option) any later version. |
| 13 | * |
| 14 | * This program is distributed in the hope that it will be useful, |
| 15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 17 | * GNU Affero General Public License for more details. |
| 18 | * |
| 19 | * You should have received a copy of the GNU Affero General Public License |
| 20 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 21 | */ |
| 22 | |
| 23 | #include <osmocom/gsm/protocol/gsm_04_08.h> |
| 24 | #include <osmocom/gsm/gsm48_arfcn_range_encode.h> |
| 25 | |
| 26 | #include <osmocom/core/utils.h> |
| 27 | |
| 28 | #include <errno.h> |
| 29 | |
| 30 | static inline int greatest_power_of_2_lesser_or_equal_to(int index) |
| 31 | { |
| 32 | int power_of_2 = 1; |
| 33 | |
| 34 | do { |
| 35 | power_of_2 *= 2; |
| 36 | } while (power_of_2 <= index); |
| 37 | |
| 38 | /* now go back one step */ |
| 39 | return power_of_2 / 2; |
| 40 | } |
| 41 | |
| 42 | static inline int mod(int data, int range) |
| 43 | { |
| 44 | int res = data % range; |
| 45 | while (res < 0) |
| 46 | res += range; |
| 47 | return res; |
| 48 | } |
| 49 | |
| 50 | /** |
| 51 | * Determine at which index to split the ARFCNs to create an |
| 52 | * equally size partition for the given range. Return -1 if |
| 53 | * no such partition exists. |
| 54 | */ |
| 55 | int osmo_gsm48_range_enc_find_index(enum osmo_gsm48_range range, const int *freqs, const int size) |
| 56 | { |
| 57 | int i, j, n; |
| 58 | |
| 59 | const int RANGE_DELTA = (range - 1) / 2; |
| 60 | |
| 61 | for (i = 0; i < size; ++i) { |
| 62 | n = 0; |
| 63 | for (j = 0; j < size; ++j) { |
| 64 | if (mod(freqs[j] - freqs[i], range) <= RANGE_DELTA) |
| 65 | n += 1; |
| 66 | } |
| 67 | |
| 68 | if (n - 1 == (size - 1) / 2) |
| 69 | return i; |
| 70 | } |
| 71 | |
| 72 | return -1; |
| 73 | } |
| 74 | |
| 75 | /* Worker for range_enc_arfcns(), do not call directly. */ |
| 76 | static int _range_enc_arfcns(enum osmo_gsm48_range range, |
| 77 | const int *arfcns, int size, int *out, |
| 78 | const int index) |
| 79 | { |
| 80 | int split_at; |
| 81 | int i; |
| 82 | |
| 83 | /* |
| 84 | * The below is a GNU extension and we can remove it when |
| 85 | * we move to a quicksort like in-situ swap with the pivot. |
| 86 | */ |
| 87 | int arfcns_left[size / 2]; |
| 88 | int arfcns_right[size / 2]; |
| 89 | int l_size; |
| 90 | int r_size; |
| 91 | int l_origin; |
| 92 | int r_origin; |
| 93 | |
| 94 | /* Now do the processing */ |
| 95 | split_at = osmo_gsm48_range_enc_find_index(range, arfcns, size); |
| 96 | if (split_at < 0) |
| 97 | return -EINVAL; |
| 98 | |
| 99 | /* we now know where to split */ |
| 100 | out[index] = 1 + arfcns[split_at]; |
| 101 | |
| 102 | /* calculate the work that needs to be done for the leafs */ |
| 103 | l_origin = mod(arfcns[split_at] + ((range - 1) / 2) + 1, range); |
| 104 | r_origin = mod(arfcns[split_at] + 1, range); |
| 105 | for (i = 0, l_size = 0, r_size = 0; i < size; ++i) { |
| 106 | if (mod(arfcns[i] - l_origin, range) < range / 2) |
| 107 | arfcns_left[l_size++] = mod(arfcns[i] - l_origin, range); |
| 108 | if (mod(arfcns[i] - r_origin, range) < range / 2) |
| 109 | arfcns_right[r_size++] = mod(arfcns[i] - r_origin, range); |
| 110 | } |
| 111 | |
| 112 | /* |
| 113 | * Now recurse and we need to make this iterative... but as the |
| 114 | * tree is balanced the stack will not be too deep. |
| 115 | */ |
| 116 | if (l_size) |
| 117 | osmo_gsm48_range_enc_arfcns(range / 2, arfcns_left, l_size, |
| 118 | out, index + greatest_power_of_2_lesser_or_equal_to(index + 1)); |
| 119 | if (r_size) |
| 120 | osmo_gsm48_range_enc_arfcns((range - 1) / 2, arfcns_right, r_size, |
| 121 | out, index + (2 * greatest_power_of_2_lesser_or_equal_to(index + 1))); |
| 122 | return 0; |
| 123 | } |
| 124 | |
| 125 | /** |
| 126 | * Range encode the ARFCN list. |
| 127 | * \param range The range to use. |
| 128 | * \param arfcns The list of ARFCNs |
| 129 | * \param size The size of the list of ARFCNs |
| 130 | * \param out Place to store the W(i) output. |
| 131 | */ |
| 132 | int osmo_gsm48_range_enc_arfcns(enum osmo_gsm48_range range, |
| 133 | const int *arfcns, int size, int *out, |
| 134 | const int index) |
| 135 | { |
| 136 | if (size <= 0) |
| 137 | return 0; |
| 138 | |
| 139 | if (size == 1) { |
| 140 | out[index] = 1 + arfcns[0]; |
| 141 | return 0; |
| 142 | } |
| 143 | |
| 144 | return _range_enc_arfcns(range, arfcns, size, out, index); |
| 145 | } |
| 146 | |
| 147 | /* |
| 148 | * The easiest is to use f0 == arfcns[0]. This means that under certain |
| 149 | * circumstances we can encode less ARFCNs than possible with an optimal f0. |
| 150 | * |
| 151 | * TODO: Solve the optimisation problem and pick f0 so that the max distance |
| 152 | * is the smallest. Taking into account the modulo operation. I think picking |
| 153 | * size/2 will be the optimal arfcn. |
| 154 | */ |
| 155 | /** |
| 156 | * This implements the range determination as described in GSM 04.08 J4. The |
| 157 | * result will be a base frequency f0 and the range to use. Note that for range |
| 158 | * 1024 encoding f0 always refers to ARFCN 0 even if it is not an element of |
| 159 | * the arfcns list. |
| 160 | * |
| 161 | * \param[in] arfcns The input frequencies, they must be sorted, lowest number first |
| 162 | * \param[in] size The length of the array |
| 163 | * \param[out] f0 The selected F0 base frequency. It might not be inside the list |
| 164 | */ |
| 165 | int osmo_gsm48_range_enc_determine_range(const int *arfcns, const int size, int *f0) |
| 166 | { |
| 167 | int max = 0; |
| 168 | |
Pau Espin Pedrol | 6c7ac6a | 2021-06-01 13:59:52 +0200 | [diff] [blame] | 169 | /* don't dereference arfcns[] array if size is 0 */ |
| 170 | if (size == 0) |
| 171 | return OSMO_GSM48_ARFCN_RANGE_128; |
| 172 | |
Stefan Sperling | fdf8b7b | 2018-07-27 12:19:15 +0200 | [diff] [blame] | 173 | /* |
| 174 | * Go for the easiest. And pick arfcns[0] == f0. |
| 175 | */ |
| 176 | max = arfcns[size - 1] - arfcns[0]; |
| 177 | *f0 = arfcns[0]; |
| 178 | |
| 179 | if (max < 128 && size <= 29) |
| 180 | return OSMO_GSM48_ARFCN_RANGE_128; |
| 181 | if (max < 256 && size <= 22) |
| 182 | return OSMO_GSM48_ARFCN_RANGE_256; |
| 183 | if (max < 512 && size <= 18) |
| 184 | return OSMO_GSM48_ARFCN_RANGE_512; |
| 185 | if (max < 1024 && size <= 17) { |
| 186 | *f0 = 0; |
| 187 | return OSMO_GSM48_ARFCN_RANGE_1024; |
| 188 | } |
| 189 | |
| 190 | return OSMO_GSM48_ARFCN_RANGE_INVALID; |
| 191 | } |
| 192 | |
| 193 | static void write_orig_arfcn(uint8_t *chan_list, int f0) |
| 194 | { |
| 195 | chan_list[0] |= (f0 >> 9) & 1; |
| 196 | chan_list[1] = (f0 >> 1); |
| 197 | chan_list[2] = (f0 & 1) << 7; |
| 198 | } |
| 199 | |
| 200 | static void write_all_wn(uint8_t *chan_list, int bit_offs, |
| 201 | int *w, int w_size, int w1_len) |
| 202 | { |
| 203 | int octet_offs = 0; /* offset into chan_list */ |
| 204 | int wk_len = w1_len; /* encoding size in bits of w[k] */ |
| 205 | int k; /* 1 based */ |
| 206 | int level = 0; /* tree level, top level = 0 */ |
| 207 | int lvl_left = 1; /* nodes per tree level */ |
| 208 | |
| 209 | /* W(2^i) to W(2^(i+1)-1) are on w1_len-i bits when present */ |
| 210 | |
| 211 | for (k = 1; k <= w_size; k++) { |
| 212 | int wk_left = wk_len; |
| 213 | |
| 214 | while (wk_left > 0) { |
| 215 | int cur_bits = 8 - bit_offs; |
| 216 | int cur_mask; |
| 217 | int wk_slice; |
| 218 | |
| 219 | if (cur_bits > wk_left) |
| 220 | cur_bits = wk_left; |
| 221 | |
| 222 | cur_mask = ((1 << cur_bits) - 1); |
| 223 | |
| 224 | /* advance */ |
| 225 | wk_left -= cur_bits; |
| 226 | bit_offs += cur_bits; |
| 227 | |
| 228 | /* right aligned wk data for current out octet */ |
| 229 | wk_slice = (w[k-1] >> wk_left) & cur_mask; |
| 230 | |
| 231 | /* cur_bits now contains the number of bits |
| 232 | * that are to be copied from wk to the chan_list. |
| 233 | * wk_left is set to the number of bits that must |
| 234 | * not yet be copied. |
| 235 | * bit_offs points after the bit area that is going to |
| 236 | * be overwritten: |
| 237 | * |
| 238 | * wk_left |
| 239 | * | |
| 240 | * v |
| 241 | * wk: WWWWWWWWWWW |
| 242 | * |||||<-- wk_slice, cur_bits=5 |
| 243 | * --WWWWW- |
| 244 | * ^ |
| 245 | * | |
| 246 | * bit_offs |
| 247 | */ |
| 248 | |
| 249 | chan_list[octet_offs] &= ~(cur_mask << (8 - bit_offs)); |
| 250 | chan_list[octet_offs] |= wk_slice << (8 - bit_offs); |
| 251 | |
| 252 | /* adjust output */ |
| 253 | if (bit_offs == 8) { |
| 254 | bit_offs = 0; |
| 255 | octet_offs += 1; |
| 256 | } |
| 257 | } |
| 258 | |
| 259 | /* adjust bit sizes */ |
| 260 | lvl_left -= 1; |
| 261 | if (!lvl_left) { |
| 262 | /* completed tree level, advance to next */ |
| 263 | level += 1; |
| 264 | lvl_left = 1 << level; |
| 265 | wk_len -= 1; |
| 266 | } |
| 267 | } |
| 268 | } |
| 269 | |
| 270 | int osmo_gsm48_range_enc_128(uint8_t *chan_list, int f0, int *w) |
| 271 | { |
| 272 | chan_list[0] = 0x8C; |
| 273 | write_orig_arfcn(chan_list, f0); |
| 274 | |
| 275 | write_all_wn(&chan_list[2], 1, w, 28, 7); |
| 276 | return 0; |
| 277 | } |
| 278 | |
| 279 | int osmo_gsm48_range_enc_256(uint8_t *chan_list, int f0, int *w) |
| 280 | { |
| 281 | chan_list[0] = 0x8A; |
| 282 | write_orig_arfcn(chan_list, f0); |
| 283 | |
| 284 | write_all_wn(&chan_list[2], 1, w, 21, 8); |
| 285 | return 0; |
| 286 | } |
| 287 | |
| 288 | int osmo_gsm48_range_enc_512(uint8_t *chan_list, int f0, int *w) |
| 289 | { |
| 290 | chan_list[0] = 0x88; |
| 291 | write_orig_arfcn(chan_list, f0); |
| 292 | |
| 293 | write_all_wn(&chan_list[2], 1, w, 17, 9); |
| 294 | return 0; |
| 295 | } |
| 296 | |
| 297 | int osmo_gsm48_range_enc_1024(uint8_t *chan_list, int f0, int f0_included, int *w) |
| 298 | { |
| 299 | chan_list[0] = 0x80 | (f0_included << 2); |
| 300 | |
| 301 | write_all_wn(&chan_list[0], 6, w, 16, 10); |
| 302 | return 0; |
| 303 | } |
| 304 | |
| 305 | int osmo_gsm48_range_enc_filter_arfcns(int *arfcns, const int size, const int f0, int *f0_included) |
| 306 | { |
| 307 | int i, j = 0; |
| 308 | *f0_included = 0; |
| 309 | |
| 310 | for (i = 0; i < size; ++i) { |
| 311 | /* |
| 312 | * Appendix J.4 says the following: |
| 313 | * All frequencies except F(0), minus F(0) + 1. |
| 314 | * I assume we need to exclude it here. |
| 315 | */ |
| 316 | if (arfcns[i] == f0) { |
| 317 | *f0_included = 1; |
| 318 | continue; |
| 319 | } |
| 320 | |
| 321 | arfcns[j++] = mod(arfcns[i] - (f0 + 1), 1024); |
| 322 | } |
| 323 | |
| 324 | return j; |
| 325 | } |