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bytereader: Use pointer instead of index access

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Currently the scan uses Boyer-moore method and its performance is good.
but, it can be optimized from an implementation of view.

The original scan code is implemented by byte array and index-based access.
In _scan_for_start_code(), the index is increasing from start to end and the
base address of the byte array is referred to as return value.

In the case, index-based access can be replaced by pointer access, which
improve the performance by removing index-related operations.

Its performace is enhanced by approximately 8% on arm-based embedded devices.
Although it seems trivial, it can affect the overall performance because the
_scan_for_start_code() function is very often called when H.264/H.265 video is
played.

In addition, the technique can apply for all architectures and it is good in
view of readability and maintainability.

https://bugzilla.gnome.org/show_bug.cgi?id=731442
This commit is contained in:
Sungho Bae 2014-06-10 09:35:38 -04:00 committed by Nicolas Dufresne
parent 12088d87bb
commit d3b2f6e4b8
1 changed files with 10 additions and 12 deletions
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22
libs/gst/base/gstbytereader.c
View file

@ -775,23 +775,21 @@ gst_byte_reader_dup_data (GstByteReader * reader, guint size, guint8 ** val)
static inline gint
_scan_for_start_code (const guint8 * data, guint offset, guint size)
{
guint i = 0;
guint8 *pdata = (guint8 *) data;
guint8 *pend = (guint8 *) (data + size - 4);
while (i <= (size - 4)) {
if (data[i + 2] > 1) {
i += 3;
} else if (data[i + 1]) {
i += 2;
} else if (data[i] || data[i + 2] != 1) {
i++;
while (pdata <= pend) {
if (pdata[2] > 1) {
pdata += 3;
} else if (pdata[1]) {
pdata += 2;
} else if (*pdata || pdata[2] != 1) {
pdata++;
} else {
break;
return (pdata - data + offset);
}
}
if (i <= (size - 4))
return i + offset;
/* nothing found */
return -1;
}