bitvec: Introduce bitvec_get_nth_set_bit() function

This is particularly important for determining the ARFCN for cells
reported in 04.08 MEAS REP.

2 files changed, 19 insertions, 0 deletions

diff --git a/openbsc/include/openbsc/bitvec.h b/openbsc/include/openbsc/bitvec.h
index a365e2a2d..b35aebf16 100644
--- a/openbsc/include/openbsc/bitvec.h
+++ b/openbsc/include/openbsc/bitvec.h
@@ -42,6 +42,9 @@ struct bitvec {
 /* check if the bit is 0 or 1 for a given position inside a bitvec */
 enum bit_value bitvec_get_bit_pos(struct bitvec *bv, unsigned int bitnr);
 
+/* get the Nth set bit inside the bit vector */
+unsigned int bitvec_get_nth_set_bit(struct bitvec *bv, unsigned int n);
+
 /* Set a bit at given position */
 int bitvec_set_bit_pos(struct bitvec *bv, unsigned int bitnum,
 			enum bit_value bit);
diff --git a/openbsc/src/bitvec.c b/openbsc/src/bitvec.c
index 8c82b8776..ad03958f3 100644
--- a/openbsc/src/bitvec.c
+++ b/openbsc/src/bitvec.c
@@ -77,6 +77,22 @@ enum bit_value bitvec_get_bit_pos(struct bitvec *bv, unsigned int bitnr)
 	return ZERO;
 }
 
+/* get the Nth set bit inside the bit vector */
+unsigned int bitvec_get_nth_set_bit(struct bitvec *bv, unsigned int n)
+{
+	unsigned int i, k = 0;
+
+	for (i = 0; i < bv->data_len*8; i++) {
+		if (bitvec_get_bit_pos(bv, i) == ONE) {
+			k++;
+			if (k == n)
+				return i;
+		}
+	}
+
+	return 0;
+}
+
 /* set the bit at a given position inside a bitvec */
 int bitvec_set_bit_pos(struct bitvec *bv, unsigned int bitnr,
 			enum bit_value bit)