avutil/mathematics: add av_add_stable()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

3 files changed, 29 insertions, 1 deletions

diff --git a/libavutil/mathematics.c b/libavutil/mathematics.c
index 2e0cf0cbd4..30963aa07b 100644
--- a/libavutil/mathematics.c
+++ b/libavutil/mathematics.c
@@ -174,3 +174,17 @@ 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 bfb5414312..a8b1d8eb31 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 adbe230c85..833d4ee42c 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, \