Replace mult by left shift in get_level_count_mag()

Change-Id: I58cdf4d1260759f085e12e871d48f59a89a346c4

av1/common/txb_common.h

diff --git a/av1/common/txb_common.h b/av1/common/txb_common.h
index 5620a70..cbecacb 100644
--- a/av1/common/txb_common.h
+++ b/av1/common/txb_common.h
@@ -75,15 +75,16 @@
   }
 }
 static INLINE int get_level_count_mag(int *mag, const tran_low_t *tcoeffs,
-                                      int stride, int height, int row, int col,
+                                      int bwl, int height, int row, int col,
                                       int level, int (*nb_offset)[2],
                                       int nb_num) {
+  const int stride = 1 << bwl;
   int count = 0;
   *mag = 0;
   for (int idx = 0; idx < nb_num; ++idx) {
     const int ref_row = row + nb_offset[idx][0];
     const int ref_col = col + nb_offset[idx][1];
-    const int pos = ref_row * stride + ref_col;
+    const int pos = (ref_row << bwl) + ref_col;
     if (ref_row < 0 || ref_col < 0 || ref_row >= height || ref_col >= stride)
       continue;
     tran_low_t abs_coeff = abs(tcoeffs[pos]);
@@ -119,14 +120,13 @@
                                int c,  // raster order
                                const int bwl, const int height,
                                const int level) {
-  const int stride = 1 << bwl;
   const int row = c >> bwl;
   const int col = c - (row << bwl);
   const int level_minus_1 = level - 1;
   int mag;
-  int count = get_level_count_mag(&mag, tcoeffs, stride, height, row, col,
-                                  level_minus_1, base_ref_offset,
-                                  BASE_CONTEXT_POSITION_NUM);
+  int count =
+      get_level_count_mag(&mag, tcoeffs, bwl, height, row, col, level_minus_1,
+                          base_ref_offset, BASE_CONTEXT_POSITION_NUM);
   int ctx_idx = get_base_ctx_from_count_mag(row, col, count, mag, level);
   return ctx_idx;
 }
@@ -177,14 +177,13 @@
 static INLINE int get_br_ctx(const tran_low_t *tcoeffs,
                              const int c,  // raster order
                              const int bwl, const int height) {
-  const int stride = 1 << bwl;
   const int row = c >> bwl;
   const int col = c - (row << bwl);
   const int level_minus_1 = NUM_BASE_LEVELS;
   int mag;
-  const int count = get_level_count_mag(&mag, tcoeffs, stride, height, row, col,
-                                        level_minus_1, br_ref_offset,
-                                        BR_CONTEXT_POSITION_NUM);
+  const int count =
+      get_level_count_mag(&mag, tcoeffs, bwl, height, row, col, level_minus_1,
+                          br_ref_offset, BR_CONTEXT_POSITION_NUM);
   const int ctx = get_br_ctx_from_count_mag(row, col, count, mag);
   return ctx;
 }