pngdec: change parse logic

Right now in parse logic the signature is checked every time the parse function
is called, and the whole data is the scanned each and every time, even though the
data is scanned in the previous instance. Changing the logic such that, we skip
the bytes which are already scanned in the previous instances of parse. This
helps in avoiding multiple scan of already scanned data/signature.

https://bugzilla.gnome.org/show_bug.cgi?id=737708

2 files changed, 33 insertions, 24 deletions

diff --git a/ext/libpng/gstpngdec.c b/ext/libpng/gstpngdec.c
index 1135d6577..48543aa23 100644
--- a/ext/libpng/gstpngdec.c
+++ b/ext/libpng/gstpngdec.c
@@ -111,6 +111,7 @@ gst_pngdec_init (GstPngDec * pngdec)
   pngdec->color_type = -1;
 
   pngdec->image_ready = FALSE;
+  pngdec->read_data = 0;
 }
 
 static void
@@ -411,6 +412,7 @@ gst_pngdec_parse (GstVideoDecoder * decoder, GstVideoCodecFrame * frame,
   gconstpointer data;
   guint64 signature;
   gsize size;
+  GstPngDec *pngdec = (GstPngDec *) decoder;
 
   GST_VIDEO_CODEC_FRAME_SET_SYNC_POINT (frame);
 
@@ -425,39 +427,42 @@ gst_pngdec_parse (GstVideoDecoder * decoder, GstVideoCodecFrame * frame,
   data = gst_adapter_map (adapter, size);
   gst_byte_reader_init (&reader, data, size);
 
-  if (!gst_byte_reader_peek_uint64_be (&reader, &signature))
-    goto need_more_data;
+  if (pngdec->read_data == 0) {
+    if (!gst_byte_reader_peek_uint64_be (&reader, &signature))
+      goto need_more_data;
 
-  if (signature != PNG_SIGNATURE) {
-    for (;;) {
-      guint offset;
+    if (signature != PNG_SIGNATURE) {
+      for (;;) {
+        guint offset;
 
-      offset = gst_byte_reader_masked_scan_uint32 (&reader, 0xffffffff,
-          0x89504E47, 0, gst_byte_reader_get_remaining (&reader));
+        offset = gst_byte_reader_masked_scan_uint32 (&reader, 0xffffffff,
+            0x89504E47, 0, gst_byte_reader_get_remaining (&reader));
 
-      if (offset == -1) {
-        gst_adapter_flush (adapter,
-            gst_byte_reader_get_remaining (&reader) - 4);
-        goto need_more_data;
-      }
+        if (offset == -1) {
+          gst_adapter_flush (adapter,
+              gst_byte_reader_get_remaining (&reader) - 4);
+          goto need_more_data;
+        }
 
-      if (!gst_byte_reader_skip (&reader, offset))
-        goto need_more_data;
+        if (!gst_byte_reader_skip (&reader, offset))
+          goto need_more_data;
 
-      if (!gst_byte_reader_peek_uint64_be (&reader, &signature))
-        goto need_more_data;
+        if (!gst_byte_reader_peek_uint64_be (&reader, &signature))
+          goto need_more_data;
 
-      if (signature == PNG_SIGNATURE) {
-        /* We're skipping, go out, we'll be back */
-        gst_adapter_flush (adapter, gst_byte_reader_get_pos (&reader));
-        goto need_more_data;
+        if (signature == PNG_SIGNATURE) {
+          /* We're skipping, go out, we'll be back */
+          gst_adapter_flush (adapter, gst_byte_reader_get_pos (&reader));
+          goto need_more_data;
+        }
+        if (!gst_byte_reader_skip (&reader, 4))
+          goto need_more_data;
       }
-      if (!gst_byte_reader_skip (&reader, 4))
-        goto need_more_data;
     }
+    pngdec->read_data = 8;
   }
 
-  if (!gst_byte_reader_skip (&reader, 8))
+  if (!gst_byte_reader_skip (&reader, pngdec->read_data))
     goto need_more_data;
 
   for (;;) {
@@ -477,8 +482,10 @@ gst_pngdec_parse (GstVideoDecoder * decoder, GstVideoCodecFrame * frame,
       toadd = gst_byte_reader_get_pos (&reader);
       GST_DEBUG_OBJECT (decoder, "Have complete frame of size %" G_GSIZE_FORMAT,
           toadd);
+      pngdec->read_data = 0;
       goto have_full_frame;
-    }
+    } else
+      pngdec->read_data += length + 12;
   }
 
   g_assert_not_reached ();
@@ -591,6 +598,7 @@ gst_pngdec_libpng_clear (GstPngDec * pngdec)
   }
 
   pngdec->color_type = -1;
+  pngdec->read_data = 0;
 }
 
 static gboolean
diff --git a/ext/libpng/gstpngdec.h b/ext/libpng/gstpngdec.h
index d89323aec..a995851bb 100644
--- a/ext/libpng/gstpngdec.h
+++ b/ext/libpng/gstpngdec.h
@@ -56,6 +56,7 @@ struct _GstPngDec
   gint color_type;
 
   gboolean image_ready;
+  gsize read_data;
 };
 
 struct _GstPngDecClass