[FFmpeg-cvslog] mpegts: Remove one 64-bit integer modulus operation per packet

[Ben Avison]

ffmpeg | branch: master | Ben Avison <bavison at riscosopen.org> | Mon Aug  5 13:12:49 2013 +0100| [a22ae9f0c579793f411e2bd7a8db557091a3a4ae] | committer: Martin Storsjö

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 at martin.st>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=a22ae9f0c579793f411e2bd7a8db557091a3a4ae
---

 libavcodec/mathops.h |    9 +++++++++
 libavformat/mpegts.c |    5 ++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/libavcodec/mathops.h b/libavcodec/mathops.h
index 551017e..8a2ce90 100644
--- a/libavcodec/mathops.h
+++ b/libavcodec/mathops.h
@@ -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;
diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index 7a74712..eecf246 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -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) {