[PATCH 5/7] si: Fix range1024 encoding

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Jacob Erlbeck jerlbeck at sysmocom.de
Wed Jan 15 13:46:13 UTC 2014


f0 is currently set to arfcns[0] in range_enc_determine_range(),
while GSM 04.08 requires f0 to be ARFCN 0 in range1024 encoding.

This patch modifies range_enc_determine_range() to force f0 to be 0
if this encoding is used. This way the case distinction in
range_enc_filter_arfcns() is not longer necessary.

Sponsored-by: On-Waves ehf
---
 openbsc/include/openbsc/arfcn_range_encode.h |    2 +-
 openbsc/src/libbsc/arfcn_range_encode.c      |   44 +++++++++++---------------
 openbsc/src/libbsc/system_information.c      |    2 +-
 openbsc/tests/gsm0408/gsm0408_test.c         |   24 +++++++-------
 4 files changed, 33 insertions(+), 39 deletions(-)

diff --git a/openbsc/include/openbsc/arfcn_range_encode.h b/openbsc/include/openbsc/arfcn_range_encode.h
index 7a6fff0..bd85d6a 100644
--- a/openbsc/include/openbsc/arfcn_range_encode.h
+++ b/openbsc/include/openbsc/arfcn_range_encode.h
@@ -16,7 +16,7 @@ enum {
 int range_enc_determine_range(const int *arfcns, int size, int *f0_out);
 int range_enc_arfcns(const int rng, const int *arfcns, int sze, int *out, int idx);
 int range_enc_find_index(const int rng, const int *arfcns, int size);
-int range_enc_filter_arfcns(const int rng, int *arfcns, const int sze, const int f0, int *f0_included);
+int range_enc_filter_arfcns(int *arfcns, const int sze, const int f0, int *f0_included);
 
 int range_enc_range128(uint8_t *chan_list, int f0, int *w);
 int range_enc_range256(uint8_t *chan_list, int f0, int *w);
diff --git a/openbsc/src/libbsc/arfcn_range_encode.c b/openbsc/src/libbsc/arfcn_range_encode.c
index 9177546..a047a06 100644
--- a/openbsc/src/libbsc/arfcn_range_encode.c
+++ b/openbsc/src/libbsc/arfcn_range_encode.c
@@ -144,7 +144,9 @@ int range_enc_arfcns(const int range,
  */
 /**
  * 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.
+ * 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
@@ -166,8 +168,10 @@ int range_enc_determine_range(const int *arfcns, const int size, int *f0)
 		return ARFCN_RANGE_256;
 	if (max < 512 && size <= 18)
 		return ARFCN_RANGE_512;
-	if (max < 1024 && size <= 17)
+	if (max < 1024 && size <= 17) {
+		*f0 = 0;
 		return ARFCN_RANGE_1024;
+	}
 
 	return ARFCN_RANGE_INVALID;
 }
@@ -271,34 +275,24 @@ int range_enc_range1024(uint8_t *chan_list, int f0, int f0_included, int *w)
 	return -1;
 }
 
-int range_enc_filter_arfcns(const int range, int *arfcns,
-			const int size, const int f0, int *f0_included)
+int range_enc_filter_arfcns(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);
+	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;
diff --git a/openbsc/src/libbsc/system_information.c b/openbsc/src/libbsc/system_information.c
index 5f46bf9..95ac736 100644
--- a/openbsc/src/libbsc/system_information.c
+++ b/openbsc/src/libbsc/system_information.c
@@ -197,7 +197,7 @@ static int enc_freq_lst_range(uint8_t *chan_list,
 	 * 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,
+	arfcns_used = range_enc_filter_arfcns(arfcns, arfcns_used,
 				f0, &f0_included);
 
 	memset(w, 0, sizeof(w));
diff --git a/openbsc/tests/gsm0408/gsm0408_test.c b/openbsc/tests/gsm0408/gsm0408_test.c
index 3a6bbdd..894eb0f 100644
--- a/openbsc/tests/gsm0408/gsm0408_test.c
+++ b/openbsc/tests/gsm0408/gsm0408_test.c
@@ -152,12 +152,12 @@ static int test_single_range_encoding(int range, const int *orig_arfcns,
 	arfcns_used = arfcns_num;
 	memmove(arfcns, orig_arfcns, sizeof(arfcns));
 
-	f0 = arfcns[0];
+	f0 = range == ARFCN_RANGE_1024 ? 0 : arfcns[0];
 	/*
 	 * 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,
+	arfcns_used = range_enc_filter_arfcns(arfcns, arfcns_used,
 					      f0, &f0_included);
 
 	memset(w, 0, sizeof(w));
@@ -354,28 +354,28 @@ static void test_arfcn_filter()
 
 	/* check that the arfcn is taken out. f0_included is only set for Range1024 */
 	f0_included = 24;
-	res = range_enc_filter_arfcns(ARFCN_RANGE_512, arfcns, ARRAY_SIZE(arfcns),
+	res = range_enc_filter_arfcns(arfcns, ARRAY_SIZE(arfcns),
 			arfcns[0], &f0_included);
 	VERIFY(res, ==, ARRAY_SIZE(arfcns) - 1);
-	VERIFY(f0_included, ==, 0);
+	VERIFY(f0_included, ==, 1);
 	for (i = 0; i < res; ++i)
 		VERIFY(arfcns[i], ==, ((i+2) * 2) - (2+1));
 
-	/* check with range1024 */
+	/* check with range1024, ARFCN 0 is included */
 	for (i = 0; i < ARRAY_SIZE(arfcns); ++i)
-		arfcns[i] = (i + 1) * 2;
-	res = range_enc_filter_arfcns(ARFCN_RANGE_1024, arfcns, ARRAY_SIZE(arfcns),
-			arfcns[0], &f0_included);
+		arfcns[i] = i * 2;
+	res = range_enc_filter_arfcns(arfcns, ARRAY_SIZE(arfcns),
+			0, &f0_included);
 	VERIFY(res, ==, ARRAY_SIZE(arfcns) - 1);
 	VERIFY(f0_included, ==, 1);
 	for (i = 0; i < res; ++i)
-		VERIFY(arfcns[i], ==, ((i + 2) * 2) - 1);
+		VERIFY(arfcns[i], ==, (i + 1) * 2 - 1);
 
-	/* check with range1024, not included */
+	/* check with range1024, ARFCN 0 not included */
 	for (i = 0; i < ARRAY_SIZE(arfcns); ++i)
 		arfcns[i] = (i + 1) * 2;
-	res = range_enc_filter_arfcns(ARFCN_RANGE_1024, arfcns, ARRAY_SIZE(arfcns),
-			11, &f0_included);
+	res = range_enc_filter_arfcns(arfcns, ARRAY_SIZE(arfcns),
+			0, &f0_included);
 	VERIFY(res, ==, ARRAY_SIZE(arfcns));
 	VERIFY(f0_included, ==, 0);
 	for (i = 0; i < res; ++i)
-- 
1.7.9.5





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