| /* 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 <http://www.gnu.org/licenses/>. |
| */ |
| |
| #include <openbsc/arfcn_range_encode.h> |
| #include <openbsc/debug.h> |
| |
| #include <osmocom/gsm/protocol/gsm_04_08.h> |
| |
| #include <osmocom/core/utils.h> |
| |
| 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 range_enc_find_index(const int 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; |
| } |
| |
| /** |
| * 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 range_enc_arfcns(const int 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; |
| |
| |
| /* Test the two recursion anchors and stop processing */ |
| if (size == 0) |
| return 0; |
| |
| if (size == 1) { |
| out[index] = 1 + arfcns[0]; |
| return 0; |
| } |
| |
| /* Now do the processing */ |
| split_at = range_enc_find_index(range, arfcns, size); |
| |
| /* 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. |
| */ |
| range_enc_arfcns(range / 2, arfcns_left, l_size, |
| out, index + greatest_power_of_2_lesser_or_equal_to(index + 1)); |
| 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; |
| } |
| |
| /* |
| * 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 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 ARFCN_RANGE_128; |
| if (max < 256 && size <= 22) |
| return ARFCN_RANGE_256; |
| if (max < 512 && size <= 18) |
| return ARFCN_RANGE_512; |
| if (max < 1024 && size <= 17) { |
| *f0 = 0; |
| return ARFCN_RANGE_1024; |
| } |
| |
| return 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; |
| DEBUGP(DRR, |
| "k=%d, wk_len=%d, offs=%d:%d, level=%d, " |
| "lvl_left=%d\n", |
| k, wk_len, octet_offs, bit_offs, level, lvl_left); |
| |
| 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); |
| |
| DEBUGP(DRR, |
| " wk_left=%d, cur_bits=%d, offs=%d:%d\n", |
| wk_left, cur_bits, octet_offs, bit_offs); |
| |
| /* 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 |
| */ |
| |
| DEBUGP(DRR, |
| " wk=%02x, slice=%02x/%02x, cl=%02x\n", |
| w[k-1], wk_slice, cur_mask, wk_slice << (8 - 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 range_enc_range128(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 range_enc_range256(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 range_enc_range512(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 range_enc_range1024(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 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; |
| } |