Add get_br_count_mag()

This will speed up lv_map encoder time by 1.5%

Change-Id: Ia9f7634bae221d2fb8fb7dc6f3202c6bacdd5b32

av1/common/txb_common.h

diff --git a/av1/common/txb_common.h b/av1/common/txb_common.h
index 562b9fb..6dde2a0 100644
--- a/av1/common/txb_common.h
+++ b/av1/common/txb_common.h
@@ -179,6 +179,33 @@
 #define BR_MAG_OFFSET 1
 // TODO(angiebird): optimize this function by using a table to map from
 // count/mag to ctx
+
+static INLINE int get_br_count_mag(int *mag, const tran_low_t *tcoeffs, int bwl,
+                                   int height, int row, int col, int level) {
+  mag[0] = 0;
+  mag[1] = 0;
+  int count = 0;
+  for (int idx = 0; idx < BR_CONTEXT_POSITION_NUM; ++idx) {
+    const int ref_row = row + br_ref_offset[idx][0];
+    const int ref_col = col + br_ref_offset[idx][1];
+    if (ref_row < 0 || ref_col < 0 || ref_row >= height ||
+        ref_col >= (1 << bwl))
+      continue;
+    const int pos = (ref_row << bwl) + ref_col;
+    tran_low_t abs_coeff = abs(tcoeffs[pos]);
+    count += abs_coeff > level;
+    if (br_ref_offset[idx][0] >= 0 && br_ref_offset[idx][1] >= 0) {
+      if (abs_coeff > mag[0]) {
+        mag[0] = abs_coeff;
+        mag[1] = 1;
+      } else if (abs_coeff == mag[0]) {
+        ++mag[1];
+      }
+    }
+  }
+  return count;
+}
+
 static INLINE int get_br_ctx_from_count_mag(int row, int col, int count,
                                             int mag) {
   int offset = 0;

av1/encoder/encodetxb.c

diff --git a/av1/encoder/encodetxb.c b/av1/encoder/encodetxb.c
index f152b43..35edbec 100644
--- a/av1/encoder/encodetxb.c
+++ b/av1/encoder/encodetxb.c
@@ -476,10 +476,8 @@
     if (!has_br(qcoeff[coeff_idx])) continue;
     int *br_count = txb_cache->br_count_arr + coeff_idx;
     int *br_mag = txb_cache->br_mag_arr[coeff_idx];
-    *br_count = get_level_count(qcoeff, bwl, height, row, col, NUM_BASE_LEVELS,
-                                br_ref_offset, BR_CONTEXT_POSITION_NUM);
-    get_mag(br_mag, qcoeff, bwl, height, row, col, br_ref_offset,
-            BR_CONTEXT_POSITION_NUM);
+    *br_count = get_br_count_mag(br_mag, qcoeff, bwl, height, row, col,
+                                 NUM_BASE_LEVELS);
     txb_cache->br_ctx_arr[coeff_idx] =
         get_br_ctx_from_count_mag(row, col, *br_count, br_mag[0]);
   }