[FFmpeg-devel] [PATCH 1/3] avutil/mathematics: add av_add_stable()

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
---
 doc/APIchanges          |    3 +++
 libavutil/mathematics.c |   14 ++++++++++++++
 libavutil/mathematics.h |   14 ++++++++++++++
 libavutil/version.h     |    2 +-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 21a8c4c..a150176 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -15,6 +15,9 @@ libavutil:     2012-10-22
 
 API changes, most recent first:
 
+2014-01-XX - xxxxxxx - lavu 52.60.100 - mathematics.h
+  Add av_add_stable() function.
+
 2013-12-22 - xxxxxxx - lavu 52.59.100 - avstring.h
   Add av_strnlen() function.
 
diff --git a/libavutil/mathematics.c b/libavutil/mathematics.c
index f9cf87d..b228a48 100644
--- a/libavutil/mathematics.c
+++ b/libavutil/mathematics.c
@@ -171,3 +171,17 @@ simple_round:
 
     return av_rescale_q(this, fs_tb, out_tb);
 }
+
+int64_t av_add_stable(AVRational ts_tb, int64_t ts, AVRational inc_tb, int64_t inc)
+{
+    AVRational step = av_mul_q(inc_tb, (AVRational) {inc, 1});
+
+    if (av_cmp_q(step, ts_tb) < 0) {
+        //increase step is too small for even 1 step to be representable
+        return ts;
+    } else {
+        int64_t old = av_rescale_q(ts, ts_tb, step);
+        int64_t old_ts = av_rescale_q(old, step, ts_tb);
+        return av_rescale_q(old + 1, step, ts_tb) + (ts - old_ts);
+    }
+}
diff --git a/libavutil/mathematics.h b/libavutil/mathematics.h
index bfb5414..a8b1d8e 100644
--- a/libavutil/mathematics.h
+++ b/libavutil/mathematics.h
@@ -141,6 +141,20 @@ int64_t av_compare_mod(uint64_t a, uint64_t b, uint64_t mod);
 int64_t av_rescale_delta(AVRational in_tb, int64_t in_ts,  AVRational fs_tb, int duration, int64_t *last, AVRational out_tb);
 
 /**
+ * Add a value to a timestamp.
+ *
+ * This function gurantees that when the same value is repeatly added that
+ * no accumulation of rounding errors occurs.
+ *
+ * @param ts Input timestamp
+ * @param ts_tb Input timestamp timebase
+ * @param inc value to add to ts
+ * @param inc_tb inc timebase
+ */
+int64_t av_add_stable(AVRational ts_tb, int64_t ts, AVRational inc_tb, int64_t inc);
+
+
+    /**
  * @}
  */
 
diff --git a/libavutil/version.h b/libavutil/version.h
index adbe230..833d4ee 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -56,7 +56,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  52
-#define LIBAVUTIL_VERSION_MINOR  59
+#define LIBAVUTIL_VERSION_MINOR  60
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
-- 
1.7.9.5