hevc/mvs: simplifying derive_spatial_merge_candidates function

cherry picked from commit 99be11cf08a5628d0bb6ac7f4958bf9dd35cda62
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/hevc_mvs.c

@@ -329,8 +329,6 @@ static void derive_spatial_merge_candidates(HEVCContext *s, int x0, int y0,
 
     const int nb_refs = (s->sh.slice_type == P_SLICE) ?
                         s->sh.nb_refs[0] : FFMIN(s->sh.nb_refs[0], s->sh.nb_refs[1]);
-    int check_MER   = 1;
-    int check_MER_1 = 1;
 
     int zero_idx = 0;
 
@@ -343,8 +341,6 @@ static void derive_spatial_merge_candidates(HEVCContext *s, int x0, int y0,
     int is_available_b1;
     int is_available_b2;
 
-    //first left spatial merge candidate
-    is_available_a1 = AVAILABLE(cand_left, A1);
 
     if (!singleMCLFlag && part_idx == 1 &&
         (lc->cu.part_mode == PART_Nx2N ||
@@ -352,84 +348,65 @@ static void derive_spatial_merge_candidates(HEVCContext *s, int x0, int y0,
          lc->cu.part_mode == PART_nRx2N) ||
         isDiffMER(s, xA1, yA1, x0, y0)) {
         is_available_a1 = 0;
+    } else {
+        is_available_a1 = AVAILABLE(cand_left, A1);
+        if (is_available_a1) {
+            mergecandlist[nb_merge_cand] = TAB_MVF_PU(A1);
+            if (merge_idx == 0) return;
+            nb_merge_cand++;
+        }
     }
 
-    if (is_available_a1) {
-        mergecandlist[0] = TAB_MVF_PU(A1);
-        if (merge_idx == 0) return;
-        nb_merge_cand++;
-    }
-
-    // above spatial merge candidate
-    is_available_b1 = AVAILABLE(cand_up, B1);
-
     if (!singleMCLFlag && part_idx == 1 &&
         (lc->cu.part_mode == PART_2NxN ||
          lc->cu.part_mode == PART_2NxnU ||
          lc->cu.part_mode == PART_2NxnD) ||
         isDiffMER(s, xB1, yB1, x0, y0)) {
         is_available_b1 = 0;
+    } else {
+        is_available_b1 = AVAILABLE(cand_up, B1);
+        if (is_available_b1 &&
+            !(is_available_a1 && COMPARE_MV_REFIDX(B1, A1))) {
+            mergecandlist[nb_merge_cand] = TAB_MVF_PU(B1);
+            if (merge_idx == nb_merge_cand) return;
+            nb_merge_cand++;
+        }
     }
 
-    if (is_available_a1 && is_available_b1)
-        check_MER = !COMPARE_MV_REFIDX(B1, A1);
-
-    if (is_available_b1 && check_MER)
-        mergecandlist[nb_merge_cand++] = TAB_MVF_PU(B1);
-
     // above right spatial merge candidate
-    check_MER = 1;
-
     is_available_b0 = AVAILABLE(cand_up_right, B0) &&
                       xB0 < s->sps->width &&
-                      PRED_BLOCK_AVAILABLE(B0);
-
-    if (isDiffMER(s, xB0, yB0, x0, y0))
-        is_available_b0 = 0;
+                      PRED_BLOCK_AVAILABLE(B0) &&
+                      !isDiffMER(s, xB0, yB0, x0, y0);
 
-    if (is_available_b1 && is_available_b0)
-        check_MER = !COMPARE_MV_REFIDX(B0, B1);
-
-    if (is_available_b0 && check_MER) {
+    if (is_available_b0 &&
+        !(is_available_b1 && COMPARE_MV_REFIDX(B0, B1))) {
         mergecandlist[nb_merge_cand] = TAB_MVF_PU(B0);
         if (merge_idx == nb_merge_cand) return;
         nb_merge_cand++;
     }
 
     // left bottom spatial merge candidate
-    check_MER = 1;
-
     is_available_a0 = AVAILABLE(cand_bottom_left, A0) &&
                       yA0 < s->sps->height &&
-                      PRED_BLOCK_AVAILABLE(A0);
+                      PRED_BLOCK_AVAILABLE(A0) &&
+                      !isDiffMER(s, xA0, yA0, x0, y0);
 
-    if (isDiffMER(s, xA0, yA0, x0, y0))
-        is_available_a0 = 0;
-
-    if (is_available_a1 && is_available_a0)
-        check_MER = !COMPARE_MV_REFIDX(A0, A1);
-
-    if (is_available_a0 && check_MER) {
+    if (is_available_a0 &&
+        !(is_available_a1 && COMPARE_MV_REFIDX(A0, A1))) {
         mergecandlist[nb_merge_cand] = TAB_MVF_PU(A0);
         if (merge_idx == nb_merge_cand) return;
         nb_merge_cand++;
     }
 
     // above left spatial merge candidate
-    check_MER = 1;
-
-    is_available_b2 = AVAILABLE(cand_up_left, B2);
-
-    if (isDiffMER(s, xB2, yB2, x0, y0))
-        is_available_b2 = 0;
-
-    if (is_available_a1 && is_available_b2)
-        check_MER = !COMPARE_MV_REFIDX(B2, A1);
-
-    if (is_available_b1 && is_available_b2)
-        check_MER_1 = !COMPARE_MV_REFIDX(B2, B1);
+    is_available_b2 = AVAILABLE(cand_up_left, B2) &&
+                      !isDiffMER(s, xB2, yB2, x0, y0);
 
-    if (is_available_b2 && check_MER && check_MER_1 && nb_merge_cand != 4) {
+    if (is_available_b2 &&
+        !(is_available_a1 && COMPARE_MV_REFIDX(B2, A1)) &&
+        !(is_available_b1 && COMPARE_MV_REFIDX(B2, B1)) &&
+        nb_merge_cand != 4) {
         mergecandlist[nb_merge_cand] = TAB_MVF_PU(B2);
         if (merge_idx == nb_merge_cand) return;
         nb_merge_cand++;