| /* 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. |
| * |
| * \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) |
| return ARFCN_RANGE_1024; |
| |
| return ARFCN_RANGE_INVALID; |
| } |
| |
| /* |
| * The below is easier is to write in four methods than |
| * to use the max_bits. The encoding is so screwed.. as |
| * the bits need to be put in place in the wrong order.. |
| */ |
| #define HIGH_BITS(w, index, bits, offset) \ |
| (w[index - 1] >> (bits - offset)) |
| #define LOW_BITS(w, index, bits, offset) \ |
| (w[index - 1]) |
| |
| 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; |
| } |
| |
| int range_enc_range128(uint8_t *chan_list, int f0, int *w) |
| { |
| chan_list[0] = 0x8C; |
| write_orig_arfcn(chan_list, f0); |
| |
| LOGP(DRR, LOGL_ERROR, "Range128 encoding is not implemented.\n"); |
| return -1; |
| } |
| |
| int range_enc_range256(uint8_t *chan_list, int f0, int *w) |
| { |
| chan_list[0] = 0x8A; |
| write_orig_arfcn(chan_list, f0); |
| |
| LOGP(DRR, LOGL_ERROR, "Range256 encoding is not implemented.\n"); |
| return -1; |
| } |
| |
| int range_enc_range512(uint8_t *chan_list, int f0, int *w) |
| { |
| struct gsm48_range_512 *range512; |
| write_orig_arfcn(chan_list, f0); |
| |
| range512 = (struct gsm48_range_512 *) &chan_list[0]; |
| range512->form_id = chan_list[0] = 0x44; |
| |
| /* W(1) */ |
| range512->w1_hi = HIGH_BITS(w, 1, 9, 7); |
| range512->w1_lo = LOW_BITS (w, 1, 9, 2); |
| /* W(2) */ |
| range512->w2_hi = HIGH_BITS(w, 2, 8, 6); |
| range512->w2_lo = LOW_BITS (w, 2, 8, 2); |
| /* W(3) */ |
| range512->w3_hi = HIGH_BITS(w, 3, 8, 6); |
| range512->w3_lo = LOW_BITS (w, 3, 8, 2); |
| /* W(4) */ |
| range512->w4_hi = HIGH_BITS(w, 4, 7, 6); |
| range512->w4_lo = LOW_BITS (w, 4, 7, 1); |
| /* W(5) */ |
| range512->w5 = HIGH_BITS(w, 5, 7, 7); |
| /* W(6) */ |
| range512->w6 = HIGH_BITS(w, 6, 7, 7); |
| /* W(7) */ |
| range512->w7_hi = HIGH_BITS(w, 7, 7, 1); |
| range512->w7_lo = LOW_BITS (w, 7, 7, 6); |
| /* W(8) */ |
| range512->w8_hi = HIGH_BITS(w, 8, 6, 2); |
| range512->w8_lo = LOW_BITS (w, 8, 6, 4); |
| /* W(9) */ |
| range512->w9_hi = HIGH_BITS(w, 9, 6, 4); |
| range512->w9_lo = LOW_BITS(w, 9, 6, 2); |
| /* W(10) */ |
| range512->w10 = HIGH_BITS(w, 10, 6, 6); |
| /* W(11) */ |
| range512->w11 = HIGH_BITS(w, 11, 6, 6); |
| /* W(12) */ |
| range512->w12_hi = HIGH_BITS(w, 12, 6, 2); |
| range512->w12_lo = LOW_BITS (w, 12, 6, 4); |
| /* W(13) */ |
| range512->w13_hi = HIGH_BITS(w, 13, 6, 4); |
| range512->w13_lo = LOW_BITS(w, 13, 6, 2); |
| /* W(14) */ |
| range512->w14 = HIGH_BITS(w, 14, 6, 6); |
| /* W(15) */ |
| range512->w15 = HIGH_BITS(w, 15, 6, 6); |
| /* W(16) */ |
| range512->w16_hi = HIGH_BITS(w, 16, 5, 2); |
| range512->w16_lo = HIGH_BITS(w, 16, 5, 3); |
| /* W(17) */ |
| range512->w17 = HIGH_BITS(w, 17, 5, 5); |
| |
| return 0; |
| } |
| |
| int range_enc_range1024(uint8_t *chan_list, int f0, int f0_included, int *w) |
| { |
| chan_list[0] = 0x80 | (f0_included << 2); |
| |
| LOGP(DRR, LOGL_ERROR, "Range1024 encoding is not implemented.\n"); |
| return -1; |
| } |
| |
| int range_enc_filter_arfcns(const int range, int *arfcns, |
| const int size, const int f0, int *f0_included) |
| { |
| int i, j = 0; |
| *f0_included = 0; |
| |
| if (range == ARFCN_RANGE_1024) { |
| for (i = 0; i < size; ++i) { |
| if (arfcns[i] == f0) { |
| *f0_included = 1; |
| continue; |
| } |
| |
| /* copy and subtract */ |
| arfcns[j++] = mod(arfcns[i] - 1, 1024); |
| } |
| } else { |
| 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) |
| continue; |
| |
| arfcns[j++] = mod(arfcns[i] - (f0 + 1), 1024); |
| } |
| } |
| |
| return j; |
| } |