si: Partially implement the range encoding for the SI.

I saw the old copy of the "Appendix J" code too late and I have
discovered some quirks and I am more familar with my implementation.
Most noticable 'w' only needs to be as big as the input arfcn but
requires the 'w' to be initialized. The power_of_2 implementation
differs as well (mine matches the output of wirehsark).

The f0 could be chosen in a better way but right now picking
the lower bound is the easiest. It is not clear if to use
modulo if the range is chosen in the middle. This can be improved
in the future. Right now I have no bit fiddling for range128, 256
and 1024 as I was running out of time.

1 files changed, 111 insertions, 25 deletions

diff --git a/openbsc/src/libbsc/system_information.c b/openbsc/src/libbsc/system_information.c
index 08c4fd18a..702924135 100644
--- a/openbsc/src/libbsc/system_information.c
+++ b/openbsc/src/libbsc/system_information.c
@@ -2,6 +2,7 @@
  * 3GPP TS 04.08 version 7.21.0 Release 1998 / ETSI TS 100 940 V7.21.0 */
 
 /* (C) 2008-2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2012 Holger Hans Peter Freyther
  *
  * All Rights Reserved
  *
@@ -34,6 +35,7 @@
 #include <openbsc/gsm_data.h>
 #include <openbsc/abis_rsl.h>
 #include <openbsc/rest_octets.h>
+#include <openbsc/arfcn_range_encode.h>
 
 
 /* Frequency Lists as per TS 04.08 10.5.2.13 */
@@ -88,11 +90,105 @@ static int freq_list_bmrel_set_arfcn(uint8_t *chan_list, unsigned int arfcn)
 	return 0;
 }
 
+/* generate a variable bitmap */
+static int enc_freq_lst_var_bitmap(uint8_t *chan_list,
+				struct bitvec *bv, const struct gsm_bts *bts,
+				int bis, int ter, int min, int pgsm)
+{
+	int i;
+
+	/* set it to 'Variable bitmap format' */
+	chan_list[0] = 0x8e;
+
+	chan_list[0] |= (min >> 9) & 1;
+	chan_list[1] = (min >> 1);
+	chan_list[2] = (min & 1) << 7;
+
+	for (i = 0; i < bv->data_len*8; i++) {
+		/* see notes in bitvec2freq_list */
+		if (bitvec_get_bit_pos(bv, i)
+		 && ((!bis && !ter && gsm_arfcn2band(i) == bts->band)
+		  || (bis && pgsm && gsm_arfcn2band(i) == bts->band && (i < 1 || i > 124))
+		  || (ter && gsm_arfcn2band(i) != bts->band))) {
+			int rc = freq_list_bmrel_set_arfcn(chan_list, i);
+			if (rc < 0)
+				return rc;
+		}
+	}
+
+	return 0;
+}
+
+/* generate a frequency list with the range 512 format */
+static int enc_freq_lst_range(uint8_t *chan_list,
+				struct bitvec *bv, const struct gsm_bts *bts,
+				int bis, int ter, int pgsm)
+{
+	int arfcns[RANGE_ENC_MAX_ARFCNS];
+	int w[RANGE_ENC_MAX_ARFCNS];
+	int f0_included = 0;
+	int arfcns_used = 0;
+	int i, rc, range, f0;
+
+	/*
+	 * Select ARFCNs according to the rules in bitvec2freq_list
+	 */
+	for (i = 0; i < bv->data_len * 8; ++i) {
+		/* More ARFCNs than the maximum */
+		if (arfcns_used > ARRAY_SIZE(arfcns))
+			return -1;
+		/* Check if we can select it? */
+		if (bitvec_get_bit_pos(bv, i)
+		 && ((!bis && !ter && gsm_arfcn2band(i) == bts->band)
+		  || (bis && pgsm && gsm_arfcn2band(i) == bts->band && (i < 1 || i > 124))
+		  || (ter && gsm_arfcn2band(i) != bts->band))) {
+			arfcns[arfcns_used++] = i;
+		}
+	}
+
+	/*
+	 * Check if the given list of ARFCNs can be encoded.
+	 */
+	range = range_enc_determine_range(arfcns, arfcns_used, &f0);
+	if (range == ARFCN_RANGE_INVALID)
+		return -2;
+
+	/*
+	 * Manipulate the ARFCN list according to the rules in J4 depending
+	 * on the selected range.
+	 */
+	arfcns_used = range_enc_filter_arfcns(range, arfcns, arfcns_used,
+				f0, &f0_included);
+
+	memset(w, 0, sizeof(w));
+	rc = range_enc_arfcns(range, arfcns, arfcns_used, w, 0);
+	if (rc != 0)
+		return -3;
+
+	/* Select the range and the amount of bits needed */
+	switch (range) {
+	case ARFCN_RANGE_128:
+		return range_enc_range128(chan_list, f0, w);
+		break;
+	case ARFCN_RANGE_256:
+		return range_enc_range256(chan_list, f0, w);
+		break;
+	case ARFCN_RANGE_512:
+		return range_enc_range512(chan_list, f0, w);
+		break;
+	case ARFCN_RANGE_1024:
+		return range_enc_range1024(chan_list, f0, f0_included, w);
+		break;
+	default:
+		return -4;
+	};
+}
+
 /* generate a cell channel list as per Section 10.5.2.1b of 04.08 */
 static int bitvec2freq_list(uint8_t *chan_list, struct bitvec *bv,
 			    const struct gsm_bts *bts, int bis, int ter)
 {
-	int i, rc, min = -1, max = -1, pgsm = 0;
+	int i, rc, min = -1, max = -1, pgsm = 0, arfcns = 0;
 
 	memset(chan_list, 0, 16);
 
@@ -114,9 +210,6 @@ static int bitvec2freq_list(uint8_t *chan_list, struct bitvec *bv,
 		return 0;
 	}
 
-	/* We currently only support the 'Variable bitmap format' */
-	chan_list[0] = 0x8e;
-
 	for (i = 0; i < bv->data_len*8; i++) {
 		/* in case of SI2 or SI5 allow all neighbours in same band
 		 * in case of SI*bis, allow neighbours in same band ouside pgsm
@@ -126,6 +219,9 @@ static int bitvec2freq_list(uint8_t *chan_list, struct bitvec *bv,
 		 && ((!bis && !ter && gsm_arfcn2band(i) == bts->band)
 		  || (bis && pgsm && gsm_arfcn2band(i) == bts->band && (i < 1 || i > 124))
 		  || (ter && gsm_arfcn2band(i) != bts->band))) {
+			/* count the arfcns we want to carry */
+			arfcns += 1;
+
 			/* 955..1023 < 0..885 */
 			if (min < 0)
 				min = i;
@@ -152,29 +248,19 @@ static int bitvec2freq_list(uint8_t *chan_list, struct bitvec *bv,
 		return 0;
 	}
 
-	if (((max - min) & 1023) > 111) {
-		LOGP(DRR, LOGL_ERROR, "min_arfcn=%u, max_arfcn=%u, "
-			"distance > 111\n", min, max);
-		return -EINVAL;
-	}
-
-	chan_list[0] |= (min >> 9) & 1;
-	chan_list[1] = (min >> 1);
-	chan_list[2] = (min & 1) << 7;
+	/* Now find the best encoding */
+	if (((max - min) & 1023) <= 111)
+		return enc_freq_lst_var_bitmap(chan_list, bv, bts, bis,
+				ter, min, pgsm);
 
-	for (i = 0; i < bv->data_len*8; i++) {
-		/* see notes above */
-		if (bitvec_get_bit_pos(bv, i)
-		 && ((!bis && !ter && gsm_arfcn2band(i) == bts->band)
-		  || (bis && pgsm && gsm_arfcn2band(i) == bts->band && (i < 1 || i > 124))
-		  || (ter && gsm_arfcn2band(i) != bts->band))) {
-			rc = freq_list_bmrel_set_arfcn(chan_list, i);
-			if (rc < 0)
-				return rc;
-		}
-	}
+	/* Attempt to do the range encoding */
+	rc = enc_freq_lst_range(chan_list, bv, bts, bis, ter, pgsm);
+	if (rc == 0)
+		return 0;
 
-	return 0;
+	LOGP(DRR, LOGL_ERROR, "min_arfcn=%u, max_arfcn=%u, arfcns=%d "
+		"can not generate ARFCN list", min, max, arfcns);
+	return -EINVAL;
 }
 
 /* generate a cell channel list as per Section 10.5.2.1b of 04.08 */