Fix bug in motion search

The maximum possible MV in 1/8 pel units is (1<<11), which could
cause mvcost out of its range that is 1023. Change maximum
possible MV in 1/8 pel units to (1<<11)-8 will fix this problem.

Change-Id: I5788ed1de773f66658c14f225fb4ab5b1679b74b

vp8/encoder/mcomp.h

diff --git a/vp8/encoder/mcomp.h b/vp8/encoder/mcomp.h
index 122debc..7600f87 100644
--- a/vp8/encoder/mcomp.h
+++ b/vp8/encoder/mcomp.h
@@ -24,7 +24,6 @@
 #define MAX_MVSEARCH_STEPS 8                                    // The maximum number of steps in a step search given the largest allowed initial step
 #define MAX_FULL_PEL_VAL ((1 << (MAX_MVSEARCH_STEPS+3)) - 8)    // Max full pel mv specified in 1/8 pel units
 #define MAX_FIRST_STEP (1 << (MAX_MVSEARCH_STEPS-1))            // Maximum size of the first step in full pel units
-#define MAX_POSSIBLE_MV (1 << 11)                               // Maximum MV in 1/8 pel units
 
 extern void print_mode_context(void);
 extern int vp8_mv_bit_cost(MV *mv, MV *ref, int *mvcost[2], int Weight);

vp8/encoder/rdopt.c

diff --git a/vp8/encoder/rdopt.c b/vp8/encoder/rdopt.c
index d694d39..366b875 100644
--- a/vp8/encoder/rdopt.c
+++ b/vp8/encoder/rdopt.c
@@ -1325,10 +1325,10 @@
 
         if (bsi.segment_rd < best_rd)
         {
-            int col_min = (best_ref_mv->col - MAX_POSSIBLE_MV) >>3;
-            int col_max = (best_ref_mv->col + MAX_POSSIBLE_MV) >>3;
-            int row_min = (best_ref_mv->row - MAX_POSSIBLE_MV) >>3;
-            int row_max = (best_ref_mv->row + MAX_POSSIBLE_MV) >>3;
+            int col_min = (best_ref_mv->col - MAX_FULL_PEL_VAL) >>3;
+            int col_max = (best_ref_mv->col + MAX_FULL_PEL_VAL) >>3;
+            int row_min = (best_ref_mv->row - MAX_FULL_PEL_VAL) >>3;
+            int row_max = (best_ref_mv->row + MAX_FULL_PEL_VAL) >>3;
 
             int tmp_col_min = x->mv_col_min;
             int tmp_col_max = x->mv_col_max;
@@ -1927,14 +1927,14 @@
                         x->e_mbd.mode_info_context->mbmi.ref_frame, cpi->common.ref_frame_sign_bias, &sr, &near_sadidx[0]);
 
             /* adjust mvp to make sure it is within MV range */
-            if(mvp.row > best_ref_mv.row + MAX_POSSIBLE_MV)
-                mvp.row = best_ref_mv.row + MAX_POSSIBLE_MV;
-            else if(mvp.row < best_ref_mv.row - MAX_POSSIBLE_MV)
-                mvp.row = best_ref_mv.row - MAX_POSSIBLE_MV;
-            if(mvp.col > best_ref_mv.col + MAX_POSSIBLE_MV)
-                mvp.col = best_ref_mv.col + MAX_POSSIBLE_MV;
-            else if(mvp.col < best_ref_mv.col - MAX_POSSIBLE_MV)
-                mvp.col = best_ref_mv.col - MAX_POSSIBLE_MV;
+            if(mvp.row > best_ref_mv.row + MAX_FULL_PEL_VAL)
+                mvp.row = best_ref_mv.row + MAX_FULL_PEL_VAL;
+            else if(mvp.row < best_ref_mv.row - MAX_FULL_PEL_VAL)
+                mvp.row = best_ref_mv.row - MAX_FULL_PEL_VAL;
+            if(mvp.col > best_ref_mv.col + MAX_FULL_PEL_VAL)
+                mvp.col = best_ref_mv.col + MAX_FULL_PEL_VAL;
+            else if(mvp.col < best_ref_mv.col - MAX_FULL_PEL_VAL)
+                mvp.col = best_ref_mv.col - MAX_FULL_PEL_VAL;
         }
 
         // Check to see if the testing frequency for this mode is at its max
@@ -2066,10 +2066,10 @@
                 int further_steps;
                 int n;
 
-                int col_min = (best_ref_mv.col - MAX_POSSIBLE_MV) >>3;
-                int col_max = (best_ref_mv.col + MAX_POSSIBLE_MV) >>3;
-                int row_min = (best_ref_mv.row - MAX_POSSIBLE_MV) >>3;
-                int row_max = (best_ref_mv.row + MAX_POSSIBLE_MV) >>3;
+                int col_min = (best_ref_mv.col - MAX_FULL_PEL_VAL) >>3;
+                int col_max = (best_ref_mv.col + MAX_FULL_PEL_VAL) >>3;
+                int row_min = (best_ref_mv.row - MAX_FULL_PEL_VAL) >>3;
+                int row_max = (best_ref_mv.row + MAX_FULL_PEL_VAL) >>3;
 
                 int tmp_col_min = x->mv_col_min;
                 int tmp_col_max = x->mv_col_max;