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mpegts: Remove one 64-bit integer modulus operation per packet 

The common case of the pointer having increased by one packet (which results
in no change to the modulus) can be detected with a 64-bit subtraction,
which is far cheaper than a division on many platforms.

           Before          After
           Mean   StdDev   Mean   StdDev  Change
Divisions   248.3  8.8      51.5   7.4    +381.7%
Overall    2773.2 25.6     2372.5 43.1     +16.9%

Signed-off-by: Martin Storsjö <martin@martin.st>
This commit is contained in:
Ben Avison 2013-08-05 13:12:49 +01:00 committed by Martin Storsjö
parent 43bacd5b7d
commit a22ae9f0c5
2 changed files with 13 additions and 1 deletions
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9
libavcodec/mathops.h
View File

@ -195,6 +195,15 @@ if ((y) < (x)) {\
# define FASTDIV(a,b) ((uint32_t)((((uint64_t)a) * ff_inverse[b]) >> 32))
#endif /* FASTDIV */
#ifndef MOD_UNLIKELY
# define MOD_UNLIKELY(modulus, dividend, divisor, prev_dividend) \
do { \
if ((prev_dividend) == 0 || (dividend) - (prev_dividend) != (divisor)) \
(modulus) = (dividend) % (divisor); \
(prev_dividend) = (dividend); \
} while (0)
#endif
static inline av_const unsigned int ff_sqrt(unsigned int a)
{
unsigned int b;

5
libavformat/mpegts.c
View File

@ -28,6 +28,7 @@
#include "libavutil/opt.h"
#include "libavcodec/bytestream.h"
#include "libavcodec/get_bits.h"
#include "libavcodec/mathops.h"
#include "avformat.h"
#include "mpegts.h"
#include "internal.h"
@ -98,6 +99,8 @@ struct MpegTSContext {
int raw_packet_size;
int pos47;
/** position corresponding to pos47, or 0 if pos47 invalid */
int64_t pos;
/** if true, all pids are analyzed to find streams */
int auto_guess;
@ -1694,7 +1697,7 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
return 0;
pos = avio_tell(ts->stream->pb);
ts->pos47= pos % ts->raw_packet_size;
MOD_UNLIKELY(ts->pos47, pos, ts->raw_packet_size, ts->pos);
if (tss->type == MPEGTS_SECTION) {
if (is_start) {