/* 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
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;
}