avutil/mathematics: add av_add_stable()

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

doc/APIchanges

@@ -15,6 +15,9 @@ libavutil:     2012-10-22
 
 API changes, most recent first:
 
+2014-01-04 - 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.
 

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);
+    }
+}

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);
+
+
+    /**
  * @}
  */
 

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, \