rist: Factor our seqnum extension code

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1153>

gst/rist/gstrist.h

@@ -72,4 +72,6 @@ typedef struct {
 } GstRistRtpDeextClass;
 GType gst_rist_rtp_deext_get_type (void);
 
+guint32 gst_rist_rtp_ext_seq (guint32 * extseqnum, guint16 seqnum);
+
 #endif

gst/rist/gstristplugin.c

@@ -25,6 +25,73 @@
 #include "gstrist.h"
 #include "gstroundrobin.h"
 
+/*
+ * rtp_ext_seq:
+ * @extseq: (inout): a previous extended seqs
+ * @seq: a new seq
+ *
+ * Update the @extseq field with the extended seq of @seq
+ * For the first call of the method, @extseq should point to a location
+ * with a value of -1.
+ *
+ * This function is able to handle both forward and backward seqs taking
+ * into account:
+ *   - seq wraparound making sure that the returned value is properly increased.
+ *   - seq unwraparound making sure that the returned value is properly decreased.
+ *
+ * Returns: The extended seq of @seq or 0 if the result can't go anywhere backwards.
+ *
+ * NOTE: This is a calque of gst_rtp_buffer_ext_timestamp() but with
+ * s/32/16/ and s/64/32/ and s/0xffffffff/0xffff/ and s/timestamp/seqnum/.
+ */
+guint32
+gst_rist_rtp_ext_seq (guint32 * extseqnum, guint16 seqnum)
+{
+  guint32 result, ext;
+
+  g_return_val_if_fail (extseqnum != NULL, -1);
+
+  ext = *extseqnum;
+
+  if (ext == -1) {
+    result = seqnum;
+  } else {
+    /* pick wraparound counter from previous seqnum and add to new seqnum */
+    result = seqnum + (ext & ~(0xffff));
+
+    /* check for seqnum wraparound */
+    if (result < ext) {
+      guint32 diff = ext - result;
+
+      if (diff > G_MAXINT16) {
+        /* seqnum went backwards more than allowed, we wrap around and get
+         * updated extended seqnum. */
+        result += (1 << 16);
+      }
+    } else {
+      guint32 diff = result - ext;
+
+      if (diff > G_MAXINT16) {
+        if (result < (1 << 16)) {
+          GST_WARNING
+              ("Cannot unwrap, any wrapping took place yet. Returning 0 without updating extended seqnum.");
+          return 0;
+        } else {
+          /* seqnum went forwards more than allowed, we unwrap around and get
+           * updated extended seqnum. */
+          result -= (1 << 16);
+          /* We don't want the extended seqnum storage to go back, ever */
+          return result;
+        }
+      }
+    }
+  }
+
+  *extseqnum = result;
+
+  return result;
+}
+
 static gboolean
 plugin_init (GstPlugin * plugin)
 {

gst/rist/gstristrtpext.c

@@ -87,74 +87,6 @@ G_DEFINE_TYPE_WITH_CODE (GstRistRtpExt, gst_rist_rtp_ext, GST_TYPE_ELEMENT,
         "RIST RTP Extension"));
 
 
-/*
- * rtp_ext_seq:
- * @extseq: (inout): a previous extended seqs
- * @seq: a new seq
- *
- * Update the @extseq field with the extended seq of @seq
- * For the first call of the method, @extseq should point to a location
- * with a value of -1.
- *
- * This function is able to handle both forward and backward seqs taking
- * into account:
- *   - seq wraparound making sure that the returned value is properly increased.
- *   - seq unwraparound making sure that the returned value is properly decreased.
- *
- * Returns: The extended seq of @seq or 0 if the result can't go anywhere backwards.
- *
- * NOTE: This is a calque of gst_rtp_buffer_ext_timestamp() but with
- * s/32/16/ and s/64/32/ and s/0xffffffff/0xffff/ and s/timestamp/seqnum/.
- */
-static guint32
-rtp_ext_seq (guint32 * extseqnum, guint16 seqnum)
-{
-  guint32 result, ext;
-
-  g_return_val_if_fail (extseqnum != NULL, -1);
-
-  ext = *extseqnum;
-
-  if (ext == -1) {
-    result = seqnum;
-  } else {
-    /* pick wraparound counter from previous seqnum and add to new seqnum */
-    result = seqnum + (ext & ~(0xffff));
-
-    /* check for seqnum wraparound */
-    if (result < ext) {
-      guint32 diff = ext - result;
-
-      if (diff > G_MAXINT16) {
-        /* seqnum went backwards more than allowed, we wrap around and get
-         * updated extended seqnum. */
-        result += (1 << 16);
-      }
-    } else {
-      guint32 diff = result - ext;
-
-      if (diff > G_MAXINT16) {
-        if (result < (1 << 16)) {
-          GST_WARNING
-              ("Cannot unwrap, any wrapping took place yet. Returning 0 without updating extended seqnum.");
-          return 0;
-        } else {
-          /* seqnum went forwards more than allowed, we unwrap around and get
-           * updated extended seqnum. */
-          result -= (1 << 16);
-          /* We don't want the extended seqnum storage to go back, ever */
-          return result;
-        }
-      }
-    }
-  }
-
-  *extseqnum = result;
-
-  return result;
-}
-
-
 static GstFlowReturn
 gst_rist_rtp_ext_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
 {
@@ -261,7 +193,7 @@ gst_rist_rtp_ext_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
     if (GST_BUFFER_IS_DISCONT (buffer))
       self->extseqnum = -1;
 
-    extseqnum = rtp_ext_seq (&self->extseqnum, seqnum);
+    extseqnum = gst_rist_rtp_ext_seq (&self->extseqnum, seqnum);
 
     gst_rtp_buffer_get_extension_data (&rtp, &bits, (void **) &data, &wordlen);
     GST_WRITE_UINT16_BE (data, (extseqnum >> 16));