avcodec/simple_idct_template: fix rounding of the special DC case for 10bit

MSE doesnt change for the test as the code only triggers
for very sparse matrixes
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/simple_idct_template.c

@@ -107,10 +107,10 @@ static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
 #define ROW0_MASK (0xffffLL << 48 * HAVE_BIGENDIAN)
     if (((((uint64_t *)row)[0] & ~ROW0_MASK) | ((uint64_t *)row)[1]) == 0) {
         uint64_t temp;
-        if (DC_SHIFT - extra_shift > 0) {
+        if (DC_SHIFT - extra_shift >= 0) {
             temp = (row[0] << (DC_SHIFT - extra_shift)) & 0xffff;
         } else {
-            temp = (row[0] >> (extra_shift - DC_SHIFT)) & 0xffff;
+            temp = ((row[0] + (1<<(extra_shift - DC_SHIFT-1))) >> (extra_shift - DC_SHIFT)) & 0xffff;
         }
         temp += temp << 16;
         temp += temp << 32;
@@ -124,10 +124,10 @@ static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
           ((uint32_t*)row)[3] |
           row[1])) {
         uint32_t temp;
-        if (DC_SHIFT - extra_shift > 0) {
+        if (DC_SHIFT - extra_shift >= 0) {
             temp = (row[0] << (DC_SHIFT - extra_shift)) & 0xffff;
         } else {
-            temp = (row[0] >> (extra_shift - DC_SHIFT)) & 0xffff;
+            temp = ((row[0] + (1<<(extra_shift - DC_SHIFT-1))) >> (extra_shift - DC_SHIFT)) & 0xffff;
         }
         temp += temp << 16;
         ((uint32_t*)row)[0]=((uint32_t*)row)[1] =

tests/ref/fate/prores-422_lt

 #tb 0: 100/2997
-0,          0,          0,        1,  8294400, 0xdaff4019
-0,          1,          1,        1,  8294400, 0xdaff4019
+0,          0,          0,        1,  8294400, 0x4ca110c7
+0,          1,          1,        1,  8294400, 0x4ca110c7

tests/ref/vsynth/vsynth2-prores

 af885572d77d28e5ede27932bd68cdde *tests/data/fate/vsynth2-prores.mov
 2844076 tests/data/fate/vsynth2-prores.mov
-387a3c23586c679b411c3eff2c9d9d06 *tests/data/fate/vsynth2-prores.out.rawvideo
+03fd29e3963716a09d232b6f817ecb57 *tests/data/fate/vsynth2-prores.out.rawvideo
 stddev:    1.31 PSNR: 45.77 MAXDIFF:   11 bytes:  7603200/  7603200