327 lines
8.1 KiB
C
327 lines
8.1 KiB
C
/* gsm 04.08 system information (si) encoding and decoding
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* 3gpp ts 04.08 version 7.21.0 release 1998 / etsi ts 100 940 v7.21.0 */
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/*
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* (C) 2012 Holger Hans Peter Freyther
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* (C) 2012 by On-Waves
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* All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <openbsc/arfcn_range_encode.h>
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#include <openbsc/debug.h>
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#include <osmocom/gsm/protocol/gsm_04_08.h>
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#include <osmocom/core/utils.h>
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static inline int greatest_power_of_2_lesser_or_equal_to(int index)
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{
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int power_of_2 = 1;
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do {
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power_of_2 *= 2;
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} while (power_of_2 <= index);
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/* now go back one step */
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return power_of_2 / 2;
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}
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static inline int mod(int data, int range)
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{
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int res = data % range;
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while (res < 0)
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res += range;
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return res;
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}
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/**
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* Determine at which index to split the ARFCNs to create an
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* equally size partition for the given range. Return -1 if
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* no such partition exists.
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*/
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int range_enc_find_index(enum gsm48_range range, const int *freqs, const int size)
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{
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int i, j, n;
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const int RANGE_DELTA = (range - 1) / 2;
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for (i = 0; i < size; ++i) {
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n = 0;
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for (j = 0; j < size; ++j) {
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if (mod(freqs[j] - freqs[i], range) <= RANGE_DELTA)
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n += 1;
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}
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if (n - 1 == (size - 1) / 2)
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return i;
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}
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return -1;
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}
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/**
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* Range encode the ARFCN list.
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* \param range The range to use.
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* \param arfcns The list of ARFCNs
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* \param size The size of the list of ARFCNs
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* \param out Place to store the W(i) output.
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*/
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int range_enc_arfcns(enum gsm48_range range,
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const int *arfcns, int size, int *out,
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const int index)
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{
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int split_at;
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int i;
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/*
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* The below is a GNU extension and we can remove it when
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* we move to a quicksort like in-situ swap with the pivot.
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*/
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int arfcns_left[size / 2];
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int arfcns_right[size / 2];
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int l_size;
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int r_size;
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int l_origin;
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int r_origin;
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/* Test the two recursion anchors and stop processing */
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if (size == 0)
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return 0;
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if (size == 1) {
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out[index] = 1 + arfcns[0];
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return 0;
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}
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/* Now do the processing */
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split_at = range_enc_find_index(range, arfcns, size);
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/* we now know where to split */
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out[index] = 1 + arfcns[split_at];
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/* calculate the work that needs to be done for the leafs */
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l_origin = mod(arfcns[split_at] + ((range - 1) / 2) + 1, range);
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r_origin = mod(arfcns[split_at] + 1, range);
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for (i = 0, l_size = 0, r_size = 0; i < size; ++i) {
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if (mod(arfcns[i] - l_origin, range) < range / 2)
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arfcns_left[l_size++] = mod(arfcns[i] - l_origin, range);
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if (mod(arfcns[i] - r_origin, range) < range / 2)
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arfcns_right[r_size++] = mod(arfcns[i] - r_origin, range);
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}
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/*
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* Now recurse and we need to make this iterative... but as the
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* tree is balanced the stack will not be too deep.
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*/
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if (l_size)
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range_enc_arfcns(range / 2, arfcns_left, l_size,
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out, index + greatest_power_of_2_lesser_or_equal_to(index + 1));
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if (r_size)
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range_enc_arfcns((range - 1) / 2, arfcns_right, r_size,
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out, index + (2 * greatest_power_of_2_lesser_or_equal_to(index + 1)));
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return 0;
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}
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/*
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* The easiest is to use f0 == arfcns[0]. This means that under certain
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* circumstances we can encode less ARFCNs than possible with an optimal f0.
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*
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* TODO: Solve the optimisation problem and pick f0 so that the max distance
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* is the smallest. Taking into account the modulo operation. I think picking
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* size/2 will be the optimal arfcn.
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*/
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/**
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* This implements the range determination as described in GSM 04.08 J4. The
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* result will be a base frequency f0 and the range to use. Note that for range
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* 1024 encoding f0 always refers to ARFCN 0 even if it is not an element of
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* the arfcns list.
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*
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* \param[in] arfcns The input frequencies, they must be sorted, lowest number first
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* \param[in] size The length of the array
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* \param[out] f0 The selected F0 base frequency. It might not be inside the list
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*/
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int range_enc_determine_range(const int *arfcns, const int size, int *f0)
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{
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int max = 0;
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/*
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* Go for the easiest. And pick arfcns[0] == f0.
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*/
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max = arfcns[size - 1] - arfcns[0];
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*f0 = arfcns[0];
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if (max < 128 && size <= 29)
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return ARFCN_RANGE_128;
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if (max < 256 && size <= 22)
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return ARFCN_RANGE_256;
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if (max < 512 && size <= 18)
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return ARFCN_RANGE_512;
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if (max < 1024 && size <= 17) {
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*f0 = 0;
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return ARFCN_RANGE_1024;
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}
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return ARFCN_RANGE_INVALID;
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}
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static void write_orig_arfcn(uint8_t *chan_list, int f0)
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{
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chan_list[0] |= (f0 >> 9) & 1;
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chan_list[1] = (f0 >> 1);
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chan_list[2] = (f0 & 1) << 7;
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}
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static void write_all_wn(uint8_t *chan_list, int bit_offs,
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int *w, int w_size, int w1_len)
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{
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int octet_offs = 0; /* offset into chan_list */
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int wk_len = w1_len; /* encoding size in bits of w[k] */
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int k; /* 1 based */
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int level = 0; /* tree level, top level = 0 */
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int lvl_left = 1; /* nodes per tree level */
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/* W(2^i) to W(2^(i+1)-1) are on w1_len-i bits when present */
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for (k = 1; k <= w_size; k++) {
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int wk_left = wk_len;
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DEBUGP(DRR,
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"k=%d, wk_len=%d, offs=%d:%d, level=%d, "
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"lvl_left=%d\n",
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k, wk_len, octet_offs, bit_offs, level, lvl_left);
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while (wk_left > 0) {
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int cur_bits = 8 - bit_offs;
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int cur_mask;
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int wk_slice;
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if (cur_bits > wk_left)
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cur_bits = wk_left;
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cur_mask = ((1 << cur_bits) - 1);
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DEBUGP(DRR,
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" wk_left=%d, cur_bits=%d, offs=%d:%d\n",
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wk_left, cur_bits, octet_offs, bit_offs);
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/* advance */
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wk_left -= cur_bits;
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bit_offs += cur_bits;
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/* right aligned wk data for current out octet */
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wk_slice = (w[k-1] >> wk_left) & cur_mask;
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/* cur_bits now contains the number of bits
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* that are to be copied from wk to the chan_list.
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* wk_left is set to the number of bits that must
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* not yet be copied.
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* bit_offs points after the bit area that is going to
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* be overwritten:
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*
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* wk_left
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* |
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* v
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* wk: WWWWWWWWWWW
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* |||||<-- wk_slice, cur_bits=5
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* --WWWWW-
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* ^
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* |
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* bit_offs
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*/
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DEBUGP(DRR,
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" wk=%02x, slice=%02x/%02x, cl=%02x\n",
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w[k-1], wk_slice, cur_mask, wk_slice << (8 - bit_offs));
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chan_list[octet_offs] &= ~(cur_mask << (8 - bit_offs));
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chan_list[octet_offs] |= wk_slice << (8 - bit_offs);
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/* adjust output */
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if (bit_offs == 8) {
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bit_offs = 0;
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octet_offs += 1;
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}
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}
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/* adjust bit sizes */
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lvl_left -= 1;
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if (!lvl_left) {
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/* completed tree level, advance to next */
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level += 1;
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lvl_left = 1 << level;
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wk_len -= 1;
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}
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}
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}
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int range_enc_range128(uint8_t *chan_list, int f0, int *w)
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{
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chan_list[0] = 0x8C;
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write_orig_arfcn(chan_list, f0);
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write_all_wn(&chan_list[2], 1, w, 28, 7);
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return 0;
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}
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int range_enc_range256(uint8_t *chan_list, int f0, int *w)
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{
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chan_list[0] = 0x8A;
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write_orig_arfcn(chan_list, f0);
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write_all_wn(&chan_list[2], 1, w, 21, 8);
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return 0;
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}
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int range_enc_range512(uint8_t *chan_list, int f0, int *w)
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{
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chan_list[0] = 0x88;
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write_orig_arfcn(chan_list, f0);
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write_all_wn(&chan_list[2], 1, w, 17, 9);
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return 0;
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}
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int range_enc_range1024(uint8_t *chan_list, int f0, int f0_included, int *w)
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{
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chan_list[0] = 0x80 | (f0_included << 2);
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write_all_wn(&chan_list[0], 6, w, 16, 10);
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return 0;
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}
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int range_enc_filter_arfcns(int *arfcns,
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const int size, const int f0, int *f0_included)
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{
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int i, j = 0;
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*f0_included = 0;
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for (i = 0; i < size; ++i) {
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/*
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* Appendix J.4 says the following:
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* All frequencies except F(0), minus F(0) + 1.
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* I assume we need to exclude it here.
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*/
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if (arfcns[i] == f0) {
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*f0_included = 1;
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continue;
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}
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arfcns[j++] = mod(arfcns[i] - (f0 + 1), 1024);
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}
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return j;
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}
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