+/**
+ * Number of bits we set per entry in the bloomfilter.
+ * Do not change!
+ */
+#define BLOOMFILTER_K 16
+
+
+/**
+ * How many bytes should a bloomfilter be if we have already seen
+ * entry_count responses? Note that #GNUNET_CONSTANTS_BLOOMFILTER_K
+ * gives us the number of bits set per entry. Furthermore, we should
+ * not re-size the filter too often (to keep it cheap).
+ *
+ * Since other peers will also add entries but not resize the filter,
+ * we should generally pick a slightly larger size than what the
+ * strict math would suggest.
+ *
+ * @param entry_count expected number of entries in the Bloom filter
+ * @return must be a power of two and smaller or equal to 2^15.
+ */
+static size_t
+compute_bloomfilter_size (unsigned int entry_count)
+{
+ size_t size;
+ unsigned int ideal = (entry_count * BLOOMFILTER_K) / 4;
+ uint16_t max = 1 << 15;
+
+ if (entry_count > max)
+ return max;
+ size = 8;
+ while ((size < max) && (size < ideal))
+ size *= 2;
+ if (size > max)
+ return max;
+ return size;
+}
+
+
+/**
+ * Create a new block group.
+ *
+ * @param ctx block context in which the block group is created
+ * @param type type of the block for which we are creating the group
+ * @param nonce random value used to seed the group creation
+ * @param raw_data optional serialized prior state of the group, NULL if unavailable/fresh
+ * @param raw_data_size number of bytes in @a raw_data, 0 if unavailable/fresh
+ * @param va variable arguments specific to @a type
+ * @return block group handle, NULL if block groups are not supported
+ * by this @a type of block (this is not an error)
+ */
+static struct GNUNET_BLOCK_Group *
+block_plugin_dht_create_group (void *cls,
+ enum GNUNET_BLOCK_Type type,
+ uint32_t nonce,
+ const void *raw_data,
+ size_t raw_data_size,
+ va_list va)
+{
+ unsigned int bf_size;
+ const char *guard;
+
+ guard = va_arg (va, const char *);
+ if (0 == memcmp (guard,
+ "seen-set-size",
+ strlen ("seen-set-size")))
+ bf_size = compute_bloomfilter_size (va_arg (va, unsigned int));
+ else if (0 == memcmp (guard,
+ "filter-size",
+ strlen ("filter-size")))
+ bf_size = va_arg (va, unsigned int);
+ else
+ {
+ GNUNET_break (0);
+ bf_size = 8;
+ }
+ GNUNET_break (NULL == va_arg (va, const char *));
+ return GNUNET_BLOCK_GROUP_bf_create (cls,
+ bf_size,
+ BLOOMFILTER_K,
+ type,
+ nonce,
+ raw_data,
+ raw_data_size);
+}
+