avcodec/mpegpicture: Use union for b_scratchpad and rd_scratchpad

These pointers point to the same buffers, so one can just
use a union for them and avoid synchronising one of them.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpegpicture.c

@@ -175,7 +175,6 @@ int ff_mpeg_framesize_alloc(AVCodecContext *avctx, MotionEstContext *me,
     sc->linesize = linesizeabs;
 
     me->temp            = me->scratchpad;
-    sc->rd_scratchpad   = me->scratchpad;
     sc->b_scratchpad    = me->scratchpad;
     sc->obmc_scratchpad = me->scratchpad + 16;
 

libavcodec/mpegpicture.h

@@ -33,9 +33,11 @@
 
 typedef struct ScratchpadContext {
     uint8_t *edge_emu_buffer;     ///< temporary buffer for if MVs point to out-of-frame data
-    uint8_t *rd_scratchpad;       ///< scratchpad for rate distortion mb decision
     uint8_t *obmc_scratchpad;
+    union {
         uint8_t *b_scratchpad;    ///< scratchpad used for writing into write only buffers
+        uint8_t *rd_scratchpad;   ///< scratchpad for rate distortion mb decision
+    };
     int      linesize;            ///< linesize that the buffers in this context have been allocated for
 } ScratchpadContext;
 

libavcodec/mpegvideo.c

@@ -440,7 +440,6 @@ static void free_duplicate_context(MpegEncContext *s)
     av_freep(&s->sc.edge_emu_buffer);
     av_freep(&s->me.scratchpad);
     s->me.temp =
-    s->sc.rd_scratchpad =
     s->sc.b_scratchpad =
     s->sc.obmc_scratchpad = NULL;
     s->sc.linesize = 0;