Simplify the for loop of reading lower levels

Move tcoeff reconstruction from the for loop of reading lower
levels to the loop of reading signs

This is to facilitate the potential simd optimization of
reading lower levels

Change-Id: I61e41ea95d30a948243fb13e3d708dd9860a058a

av1/decoder/decodetxb.c

diff --git a/av1/decoder/decodetxb.c b/av1/decoder/decodetxb.c
index f9d2f72..e976999 100644
--- a/av1/decoder/decodetxb.c
+++ b/av1/decoder/decodetxb.c
@@ -10,8 +10,8 @@
  */
 
 #include "aom_ports/mem.h"
-#include "av1/common/scan.h"
 #include "av1/common/idct.h"
+#include "av1/common/scan.h"
 #include "av1/common/txb_common.h"
 #include "av1/decoder/decodemv.h"
 #include "av1/decoder/decodetxb.h"
@@ -233,16 +233,24 @@
     }
     const int level =
         aom_read_symbol(r, cdf, nsymbs, ACCT_STR) + (c == *eob - 1);
+    levels[get_padded_idx(pos, bwl)] = level;
+  }
 
-    // printf("base_cdf: %d %d %2d\n", txs_ctx, plane_type, coeff_ctx);
-    // printf("base_cdf: %d %d %2d : %3d %3d %3d\n", txs_ctx, plane_type,
-    // coeff_ctx,
-    //            ec_ctx->coeff_base_cdf[txs_ctx][plane_type][coeff_ctx][0]>>7,
-    //            ec_ctx->coeff_base_cdf[txs_ctx][plane_type][coeff_ctx][1]>>7,
-    //            ec_ctx->coeff_base_cdf[txs_ctx][plane_type][coeff_ctx][2]>>7);
+  // Loop to decode all signs in the transform block,
+  // starting with the sign of the DC (if applicable)
+  for (c = 0; c < *eob; ++c) {
+    const int pos = scan[c];
+    int8_t *const sign = &signs[pos];
+    const int level = levels[get_padded_idx(pos, bwl)];
     if (level) {
-      levels[get_padded_idx(pos, bwl)] = level;
       *max_scan_line = AOMMAX(*max_scan_line, pos);
+      if (c == 0) {
+        const int dc_sign_ctx = txb_ctx->dc_sign_ctx;
+        *sign = aom_read_symbol(r, ec_ctx->dc_sign_cdf[plane_type][dc_sign_ctx],
+                                2, ACCT_STR);
+      } else {
+        *sign = aom_read_bit(r, ACCT_STR);
+      }
       if (level < 3) {
         cul_level += level;
 #if CONFIG_NEW_QUANT
@@ -257,31 +265,19 @@
         v = level * get_dqv(dequant, scan[c], iqmatrix);
         v = v >> shift;
 #endif  // CONFIG_NEW_QUANT
-        tcoeffs[pos] = v;
+        if (*sign) {
+          tcoeffs[pos] = -v;
+        } else {
+          tcoeffs[pos] = v;
+        }
       } else {
         update_pos[num_updates++] = pos;
       }
     }
   }
 
-  // Loop to decode all signs in the transform block,
-  // starting with the sign of the DC (if applicable)
-  for (c = 0; c < *eob; ++c) {
-    const int pos = scan[c];
-    int8_t *const sign = &signs[pos];
-    if (levels[get_padded_idx(pos, bwl)] == 0) continue;
-    if (c == 0) {
-      const int dc_sign_ctx = txb_ctx->dc_sign_ctx;
-      *sign = aom_read_symbol(r, ec_ctx->dc_sign_cdf[plane_type][dc_sign_ctx],
-                              2, ACCT_STR);
-    } else {
-      *sign = aom_read_bit(r, ACCT_STR);
-    }
-    if (*sign) tcoeffs[pos] = -tcoeffs[pos];
-  }
-
   if (num_updates) {
-    for (c = 0; c < num_updates; ++c) {
+    for (c = num_updates - 1; c >= 0; --c) {
       const int pos = update_pos[c];
       uint8_t *const level = &levels[get_padded_idx(pos, bwl)];
       int idx = 0;