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typefind: speed up mxf_type_find over 300 times for worst case scenarios

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* memcmp is expensive and was being abused, reduce calling it by checking
  the first byte.
* iterating one byte at at time over 64 kbites introduces a certain overhead,
  therefore we now do it in chunks of 1024 bytes

And I do mean over 300 times. The average instruction call per mxf_type_find
was previously 785685 and it's now down to 2458 :)
This commit is contained in:
Edward Hervey 2009-10-21 20:44:33 +02:00
parent c489fb01ca
commit d48d47e683
1 changed files with 21 additions and 14 deletions
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35
gst/typefind/gsttypefindfunctions.c
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@ -2697,28 +2697,35 @@ mxf_type_find (GstTypeFind * tf, gpointer ununsed)
DataScanCtx c = { 0, NULL, 0 };
while (c.offset <= MXF_MAX_PROBE_LENGTH) {
if (G_UNLIKELY (!data_scan_ctx_ensure_data (tf, &c, 16)))
guint i;
if (G_UNLIKELY (!data_scan_ctx_ensure_data (tf, &c, 1024)))
break;
if (memcmp (c.data, partition_pack_key, 13) == 0) {
/* Header partition pack? */
if (c.data[13] != 0x02)
goto advance;
/* look over in chunks of 1kbytes to avoid too much overhead */
/* Partition status */
if (c.data[14] >= 0x05)
goto advance;
for (i = 0; i < 1024 - 16; i++) {
/* Check first byte before calling more expensive memcmp function */
if (G_UNLIKELY (c.data[0] == 0x06
&& memcmp (c.data + i, partition_pack_key, 13) == 0)) {
/* Header partition pack? */
if (c.data[i + 13] != 0x02)
goto advance;
/* Reserved, must be 0x00 */
if (c.data[15] != 0x00)
goto advance;
/* Partition status */
if (c.data[i + 14] >= 0x05)
goto advance;
gst_type_find_suggest (tf, GST_TYPE_FIND_MAXIMUM, MXF_CAPS);
return;
/* Reserved, must be 0x00 */
if (c.data[i + 15] != 0x00)
goto advance;
gst_type_find_suggest (tf, GST_TYPE_FIND_MAXIMUM, MXF_CAPS);
return;
}
}
advance:
data_scan_ctx_advance (tf, &c, 1);
data_scan_ctx_advance (tf, &c, 1024 - 16);
}
}