Use standard rounding in intra filters.

Use the same rounding method that is used throughout the codebase,
where the halfway value is rounded up rather than down.

Change-Id: Ie969ed7eb9fcc88a93a90c7e274fd82f336c7e4d

vp10/common/reconintra.c

@@ -391,7 +391,6 @@ static void vp10_init_intra_predictors_internal(void) {
 
 #if CONFIG_EXT_INTRA
 #define FILTER_INTRA_PREC_BITS 10
-#define FILTER_INTRA_ROUND_VAL 511
 
 static const uint8_t ext_intra_extend_modes[FILTER_INTRA_MODES] = {
   NEED_LEFT | NEED_ABOVE,      // FILTER_DC
@@ -774,9 +773,7 @@ static void filter_intra_predictors_4tap(uint8_t *dst, ptrdiff_t stride, int bs,
     for (c = 1; c < 2 * bs + 1 - r; ++c) {
       ipred = c0 * pred[r - 1][c] + c1 * pred[r][c - 1] +
           c2 * pred[r - 1][c - 1] + c3 * pred[r - 1][c + 1];
-      pred[r][c] = ipred < 0 ?
-          -((-ipred + FILTER_INTRA_ROUND_VAL) >> FILTER_INTRA_PREC_BITS) :
-          ((ipred + FILTER_INTRA_ROUND_VAL) >> FILTER_INTRA_PREC_BITS);
+      pred[r][c] = ROUND_POWER_OF_TWO_SIGNED(ipred, FILTER_INTRA_PREC_BITS);
     }
 
   for (r = 0; r < bs; ++r) {
@@ -1050,9 +1047,7 @@ static void highbd_filter_intra_predictors_4tap(uint16_t *dst, ptrdiff_t stride,
     for (c = 1; c < 2 * bs + 1 - r; ++c) {
       ipred = c0 * pred[r - 1][c] + c1 * pred[r][c - 1] +
           c2 * pred[r - 1][c - 1] + c3 * pred[r - 1][c + 1];
-      pred[r][c] = ipred < 0 ?
-          -((-ipred + FILTER_INTRA_ROUND_VAL) >> FILTER_INTRA_PREC_BITS) :
-          ((ipred + FILTER_INTRA_ROUND_VAL) >> FILTER_INTRA_PREC_BITS);
+      pred[r][c] = ROUND_POWER_OF_TWO_SIGNED(ipred, FILTER_INTRA_PREC_BITS);
     }
 
   for (r = 0; r < bs; ++r) {

vpx_ports/mem.h

@@ -46,6 +46,11 @@
 #define ROUNDZ_POWER_OF_TWO(value, n) \
     ((n) ? (((value) + (1 << ((n) - 1))) >> (n)) : (value))
 
+/* Shift down with rounding for signed integers, for use when n > 0 */
+#define ROUND_POWER_OF_TWO_SIGNED(value, n) \
+    (((value) < 0) ? -ROUND_POWER_OF_TWO(-(value), (n)) \
+                   : ROUND_POWER_OF_TWO((value), (n)))
+
 #define ALIGN_POWER_OF_TWO(value, n) \
     (((value) + ((1 << (n)) - 1)) & ~((1 << (n)) - 1))