Add comparision function for shingles.

src/libutil/shingles.c

@@ -135,3 +135,18 @@ rspamd_shingles_default_filter (guint64 *input, gsize count,
 
 	return minimal;
 }
+
+
+gdouble rspamd_shingles_compare (const struct rspamd_shingle *a,
+		const struct rspamd_shingle *b)
+{
+	gint i, common = 0;
+
+	for (i = 0; i < RSPAMD_SHINGLE_SIZE; i ++) {
+		if (a->hashes[i] == b->hashes[i]) {
+			common ++;
+		}
+	}
+
+	return (gdouble)common / 84.0;
+}

src/libutil/shingles.h

@@ -57,6 +57,16 @@ struct rspamd_shingle* rspamd_shingles_generate (GArray *input,
 		rspamd_shingles_filter filter,
 		gpointer filterd);
 
+/**
+ * Compares two shingles and return result as a floating point value - 1.0
+ * for completely similar shingles and 0.0 for completely different ones
+ * @param a
+ * @param b
+ * @return
+ */
+gdouble rspamd_shingles_compare (const struct rspamd_shingle *a,
+		const struct rspamd_shingle *b);
+
 /**
  * Default filtering function
  */