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videoparsers: Speed up the start code search algorithm

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Based on 96a7f9c8b1

Makes it 3-4 times faster
This commit is contained in:
Edward Hervey 2011-06-12 12:55:40 +02:00
parent 7032cd12e7
commit c27b16bfe3
1 changed files with 49 additions and 4 deletions
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53
gst/videoparsers/gstmpegvideoparse.c
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@ -385,6 +385,53 @@ gst_mpegv_parse_process_sc (GstMpegvParse * mpvparse, GstBuffer * buf, gint off)
return ret;
}
static inline guint
scan_for_start_codes (const GstByteReader * reader, guint offset, guint size)
{
const guint8 *data;
guint32 state;
guint i;
g_return_val_if_fail (size > 0, -1);
g_return_val_if_fail ((guint64) offset + size <= reader->size - reader->byte,
-1);
/* we can't find the pattern with less than 4 bytes */
if (G_UNLIKELY (size < 4))
return -1;
data = reader->data + reader->byte + offset;
/* set the state to something that does not match */
state = 0xffffffff;
/* now find data */
for (i = 0; i < size; i++) {
/* throw away one byte and move in the next byte */
state = ((state << 8) | data[i]);
if (G_UNLIKELY ((state & 0xffffff00) == 0x00000100)) {
/* we have a match but we need to have skipped at
* least 4 bytes to fill the state. */
if (G_LIKELY (i >= 3))
return offset + i - 3;
}
/* Accelerate search for start code */
if (data[i] > 1) {
while (i < (size - 4) && data[i] > 1) {
if (data[i + 3] > 1)
i += 4;
else
i += 1;
}
state = 0x00000100;
}
}
/* nothing found */
return -1;
}
/* FIXME move into baseparse, or anything equivalent;
* see https://bugzilla.gnome.org/show_bug.cgi?id=650093 */
#define GST_BASE_PARSE_FRAME_FLAG_PARSING 0x10000
@ -419,8 +466,7 @@ retry:
goto next;
}
off = gst_byte_reader_masked_scan_uint32 (&reader, 0xffffff00, 0x00000100,
off, GST_BUFFER_SIZE (buf) - off);
off = scan_for_start_codes (&reader, off, GST_BUFFER_SIZE (buf) - off);
GST_LOG_OBJECT (mpvparse, "possible sync at buffer offset %d", off);
@ -453,8 +499,7 @@ next:
/* position a bit further than last sc */
off++;
/* so now we have start code at start of data; locate next start code */
off = gst_byte_reader_masked_scan_uint32 (&reader, 0xffffff00, 0x00000100,
off, GST_BUFFER_SIZE (buf) - off);
off = scan_for_start_codes (&reader, off, GST_BUFFER_SIZE (buf) - off);
GST_LOG_OBJECT (mpvparse, "next start code at %d", off);
if (off < 0) {