Update public FFmpeg header files from r16647 to r18286.

third_party/ffmpeg/include/libavutil/mathematics.h

 /*
  * copyright (c) 2005 Michael Niedermayer <michaelni@gmx.at>
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #ifndef AVUTIL_MATHEMATICS_H
 #define AVUTIL_MATHEMATICS_H
 
 #include <stdint.h>
 #include <math.h>
+#include "common.h"
 #include "rational.h"
 
 #ifndef M_E
 #define M_E            2.7182818284590452354   /* e */
 #endif
 #ifndef M_LN2
 #define M_LN2          0.69314718055994530942  /* log_e 2 */
 #endif
 #ifndef M_LN10
 #define M_LN10         2.30258509299404568402  /* log_e 10 */
 #endif
 #ifndef M_PI
 #define M_PI           3.14159265358979323846  /* pi */
 #endif
 #ifndef M_SQRT1_2
 #define M_SQRT1_2      0.70710678118654752440  /* 1/sqrt(2) */
 #endif
 
 enum AVRounding {
-    AV_ROUND_ZERO     = 0, ///< round toward zero
-    AV_ROUND_INF      = 1, ///< round away from zero
-    AV_ROUND_DOWN     = 2, ///< round toward -infinity
-    AV_ROUND_UP       = 3, ///< round toward +infinity
-    AV_ROUND_NEAR_INF = 5, ///< round to nearest and halfway cases away from zero
+    AV_ROUND_ZERO     = 0, ///< Round toward zero.
+    AV_ROUND_INF      = 1, ///< Round away from zero.
+    AV_ROUND_DOWN     = 2, ///< Round toward -infinity.
+    AV_ROUND_UP       = 3, ///< Round toward +infinity.
+    AV_ROUND_NEAR_INF = 5, ///< Round to nearest and halfway cases away from zero.
 };
 
+int64_t av_const av_gcd(int64_t a, int64_t b);
+
 /**
- * rescale a 64bit integer with rounding to nearest.
- * a simple a*b/c isn't possible as it can overflow
+ * Rescales a 64-bit integer with rounding to nearest.
+ * A simple a*b/c isn't possible as it can overflow.
  */
 int64_t av_rescale(int64_t a, int64_t b, int64_t c) av_const;
 
 /**
- * rescale a 64bit integer with specified rounding.
- * a simple a*b/c isn't possible as it can overflow
+ * Rescales a 64-bit integer with specified rounding.
+ * A simple a*b/c isn't possible as it can overflow.
  */
 int64_t av_rescale_rnd(int64_t a, int64_t b, int64_t c, enum AVRounding) av_const;
 
 /**
- * rescale a 64bit integer by 2 rational numbers.
+ * Rescales a 64-bit integer by 2 rational numbers.
  */
 int64_t av_rescale_q(int64_t a, AVRational bq, AVRational cq) av_const;
 
 #endif /* AVUTIL_MATHEMATICS_H */