You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
68 lines
2.4 KiB
68 lines
2.4 KiB
10 years ago
|
/*****************************************************************************
|
||
|
|
* startcode_helper.h: Startcodes helpers
|
||
|
|
*****************************************************************************
|
||
|
|
* Copyright (C) 2016 VideoLAN Authors
|
||
|
|
*
|
||
|
|
* This program is free software; you can redistribute it and/or modify it
|
||
|
|
* under the terms of the GNU Lesser General Public License as published by
|
||
|
|
* the Free Software Foundation; either version 2.1 of the License, or
|
||
|
|
* (at your option) any later version.
|
||
|
|
*
|
||
|
|
* This program is distributed in the hope that it will be useful,
|
||
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
|
|
* GNU Lesser General Public License for more details.
|
||
|
|
*
|
||
|
|
* You should have received a copy of the GNU Lesser General Public License
|
||
|
|
* along with this program; if not, write to the Free Software Foundation,
|
||
|
|
* Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
|
||
|
|
*****************************************************************************/
|
||
|
|
#ifndef _STARTCODE_HELPER_H
|
||
|
|
#define _STARTCODE_HELPER_H 1
|
||
|
|
|
||
|
|
/* Looks up efficiently for an AnnexB startcode 0x00 0x00 0x01
|
||
|
|
* by using a 4 times faster trick than single byte lookup.
|
||
|
|
*
|
||
|
|
* That code is adapted from libav's ff_avc_find_startcode_internal
|
||
|
|
* and i believe the trick originated from
|
||
|
|
* https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
|
||
|
|
*/
|
||
|
|
static inline const uint8_t * startcode_FindAnnexB( const uint8_t *p, const uint8_t *end )
|
||
|
|
{
|
||
|
|
const uint8_t *a = p + 4 - ((intptr_t)p & 3);
|
||
|
|
|
||
|
|
for (end -= 3; p < a && p < end; p++) {
|
||
|
|
if (p[0] == 0 && p[1] == 0 && p[2] == 1)
|
||
|
|
return p;
|
||
|
|
}
|
||
|
|
|
||
|
|
for (end -= 3; p < end; p += 4) {
|
||
|
|
uint32_t x = *(const uint32_t*)p;
|
||
|
|
if ((x - 0x01010101) & (~x) & 0x80808080)
|
||
|
|
{
|
||
|
|
/* matching DW isn't faster */
|
||
|
|
if (p[1] == 0) {
|
||
|
|
if (p[0] == 0 && p[2] == 1)
|
||
|
|
return p;
|
||
|
|
if (p[2] == 0 && p[3] == 1)
|
||
|
|
return p+1;
|
||
|
|
}
|
||
|
|
if (p[3] == 0) {
|
||
|
|
if (p[2] == 0 && p[4] == 1)
|
||
|
|
return p+2;
|
||
|
|
if (p[4] == 0 && p[5] == 1)
|
||
|
|
return p+3;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
for (end += 3; p < end; p++) {
|
||
|
|
if (p[0] == 0 && p[1] == 0 && p[2] == 1)
|
||
|
|
return p;
|
||
|
|
}
|
||
|
|
|
||
|
|
return NULL;
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|