lavfi/rotate: Avoid undefined behaviour.

Fixes the following integer overflows:
libavfilter/vf_rotate.c:273:13: runtime error: signed integer overflow: 92951468 + 2058533568 cannot be represented in type 'int'
libavfilter/vf_rotate.c:273:37: runtime error: signed integer overflow: 39684 * 54149 cannot be represented in type 'int'
libavfilter/vf_rotate.c:272:13: runtime error: signed integer overflow: 247587320 + 1900985032 cannot be represented in type 'int'
libavfilter/vf_rotate.c:272:37: runtime error: signed integer overflow: 42584 * 50430 cannot be represented in type 'int'
libavfilter/vf_rotate.c:272:50: runtime error: signed integer overflow: 65083 * 52912 cannot be represented in type 'int'
libavfilter/vf_rotate.c:273:50: runtime error: signed integer overflow: 65286 * 38044 cannot be represented in type 'int'

Fixes ticket #9799, different output with different compilers.

libavfilter/vf_rotate.c

@@ -258,8 +258,8 @@ static uint8_t *interpolate_bilinear16(uint8_t *dst_color,
 {
     int int_x = av_clip(x>>16, 0, max_x);
     int int_y = av_clip(y>>16, 0, max_y);
-    int frac_x = x&0xFFFF;
-    int frac_y = y&0xFFFF;
+    int64_t frac_x = x&0xFFFF;
+    int64_t frac_y = y&0xFFFF;
     int i;
     int int_x1 = FFMIN(int_x+1, max_x);
     int int_y1 = FFMIN(int_y+1, max_y);
@@ -269,10 +269,10 @@ static uint8_t *interpolate_bilinear16(uint8_t *dst_color,
         int s01 = AV_RL16(&src[src_linestep * int_x1 + i + src_linesize * int_y ]);
         int s10 = AV_RL16(&src[src_linestep * int_x  + i + src_linesize * int_y1]);
         int s11 = AV_RL16(&src[src_linestep * int_x1 + i + src_linesize * int_y1]);
-        int s0 = (((1<<16) - frac_x)*s00 + frac_x*s01);
-        int s1 = (((1<<16) - frac_x)*s10 + frac_x*s11);
+        int64_t s0 = (((1<<16) - frac_x)*s00 + frac_x*s01);
+        int64_t s1 = (((1<<16) - frac_x)*s10 + frac_x*s11);
 
-        AV_WL16(&dst_color[i], ((int64_t)((1<<16) - frac_y)*s0 + (int64_t)frac_y*s1) >> 32);
+        AV_WL16(&dst_color[i], (((1<<16) - frac_y)*s0 + frac_y*s1) >> 32);
     }
 
     return dst_color;