swscale/output: Fix integer overflows in yuv2rgba64_X_c_template

Fixes: signed integer overflow: -1082982400 + -1068681048 cannot be represented in type 'int'
Fixes: 69995/clusterfuzz-testcase-minimized-ffmpeg_SWS_fuzzer-6285740271534080

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/output.c

@@ -1059,8 +1059,8 @@ yuv2rgba64_X_c_template(SwsContext *c, const int16_t *lumFilter,
 
     for (i = 0; i < ((dstW + 1) >> 1); i++) {
         int j;
-        int Y1 = -0x40000000;
-        int Y2 = -0x40000000;
+        unsigned Y1 = -0x40000000;
+        unsigned Y2 = -0x40000000;
         int U  = -(128 << 23); // 19
         int V  = -(128 << 23);
         int R, G, B;
@@ -1088,9 +1088,9 @@ yuv2rgba64_X_c_template(SwsContext *c, const int16_t *lumFilter,
         }
 
         // 8 bits: 12+15=27; 16 bits: 12+19=31
-        Y1 >>= 14; // 10
+        Y1 = (int)Y1 >> 14; // 10
         Y1 += 0x10000;
-        Y2 >>= 14;
+        Y2 = (int)Y2 >> 14;
         Y2 += 0x10000;
         U  >>= 14;
         V  >>= 14;
@@ -1109,20 +1109,20 @@ yuv2rgba64_X_c_template(SwsContext *c, const int16_t *lumFilter,
         B =                            U * c->yuv2rgb_u2b_coeff;
 
         // 8 bits: 30 - 22 = 8 bits, 16 bits: 30 bits - 14 = 16 bits
-        output_pixel(&dest[0], av_clip_uintp2(((R_B + Y1) >> 14) + (1<<15), 16));
-        output_pixel(&dest[1], av_clip_uintp2(((  G + Y1) >> 14) + (1<<15), 16));
-        output_pixel(&dest[2], av_clip_uintp2(((B_R + Y1) >> 14) + (1<<15), 16));
+        output_pixel(&dest[0], av_clip_uintp2(((int)(R_B + Y1) >> 14) + (1<<15), 16));
+        output_pixel(&dest[1], av_clip_uintp2(((int)(  G + Y1) >> 14) + (1<<15), 16));
+        output_pixel(&dest[2], av_clip_uintp2(((int)(B_R + Y1) >> 14) + (1<<15), 16));
         if (eightbytes) {
             output_pixel(&dest[3], av_clip_uintp2(A1      , 30) >> 14);
-            output_pixel(&dest[4], av_clip_uintp2(((R_B + Y2) >> 14) + (1<<15), 16));
-            output_pixel(&dest[5], av_clip_uintp2(((  G + Y2) >> 14) + (1<<15), 16));
-            output_pixel(&dest[6], av_clip_uintp2(((B_R + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[4], av_clip_uintp2(((int)(R_B + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[5], av_clip_uintp2(((int)(  G + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[6], av_clip_uintp2(((int)(B_R + Y2) >> 14) + (1<<15), 16));
             output_pixel(&dest[7], av_clip_uintp2(A2      , 30) >> 14);
             dest += 8;
         } else {
-            output_pixel(&dest[3], av_clip_uintp2(((R_B + Y2) >> 14) + (1<<15), 16));
-            output_pixel(&dest[4], av_clip_uintp2(((  G + Y2) >> 14) + (1<<15), 16));
-            output_pixel(&dest[5], av_clip_uintp2(((B_R + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[3], av_clip_uintp2(((int)(R_B + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[4], av_clip_uintp2(((int)(  G + Y2) >> 14) + (1<<15), 16));
+            output_pixel(&dest[5], av_clip_uintp2(((int)(B_R + Y2) >> 14) + (1<<15), 16));
             dest += 6;
         }
     }