mpeg4parser: speed up scan for start codes

While some may be suspicious of the call to memchr, GCC is
expected to have an intrinsic definition for it, which should
see it turned into a set of asm opcodes tailored for the task.

1 files changed, 28 insertions, 4 deletions

diff --git a/gst-libs/gst/codecparsers/gstmpeg4parser.c b/gst-libs/gst/codecparsers/gstmpeg4parser.c
index 0923c103c..0827e9f0e 100644
--- a/gst-libs/gst/codecparsers/gstmpeg4parser.c
+++ b/gst-libs/gst/codecparsers/gstmpeg4parser.c
@@ -407,6 +407,32 @@ gst_mpeg4_next_resync (GstMpeg4Packet * packet,
 
 /********** API **********/
 
+static guint
+find_start_code (const guint8 * data, guint offset, guint size)
+{
+  const guint8 *start = data;
+
+  g_return_val_if_fail (size > 0, -1);
+
+  /* we can't find the pattern with less than 4 bytes */
+  if (G_UNLIKELY (size < 4))
+    return -1;
+
+  data += offset;
+  size -= 3;
+  while (size > 0) {
+    const guint8 *ptr = memchr (data, 0, size);
+    if (G_UNLIKELY (ptr == NULL))
+      return -1;
+    if (ptr[2] == 1 && ptr[1] == 0)
+      return ptr - start;
+    size -= (ptr - data) + 1;
+    data = ptr + 1;
+  }
+
+  return -1;
+}
+
 /**
  * gst_mpeg4_parse:
  * @packet: The #GstMpeg4Packet to fill
@@ -461,8 +487,7 @@ gst_mpeg4_parse (GstMpeg4Packet * packet, gboolean skip_user_data,
     first_resync_marker = TRUE;
   }
 
-  off1 = gst_byte_reader_masked_scan_uint32 (&br, 0xffffff00, 0x00000100,
-      offset, size - offset);
+  off1 = find_start_code (br.data + br.byte, offset, size - offset);
 
   if (off1 == -1) {
     GST_DEBUG ("No start code prefix in this buffer");
@@ -480,8 +505,7 @@ gst_mpeg4_parse (GstMpeg4Packet * packet, gboolean skip_user_data,
   packet->type = (GstMpeg4StartCode) (data[off1 + 3]);
 
 find_end:
-  off2 = gst_byte_reader_masked_scan_uint32 (&br, 0xffffff00, 0x00000100,
-      off1 + 4, size - off1 - 4);
+  off2 = find_start_code (br.data + br.byte, off1 + 4, size - off1 - 4);
 
   if (off2 == -1) {
     GST_DEBUG ("Packet start %d, No end found", off1 + 4);