avcodec/vc1_block: Optimize vc1_decode_ac_coeff()

Avoid branches in sign handling
Move local variables to where they are used
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vc1_block.c

@@ -487,17 +487,16 @@ static void vc1_decode_ac_coeff(VC1Context *v, int *last, int *skip,
                                 int *value, int codingset)
 {
     GetBitContext *gb = &v->s.gb;
-    int index, escape, run = 0, level = 0, lst = 0;
+    int index, run, level, lst, sign;
 
     index = get_vlc2(gb, ff_vc1_ac_coeff_table[codingset].table, AC_VLC_BITS, 3);
     if (index != ff_vc1_ac_sizes[codingset] - 1) {
         run   = vc1_index_decode_table[codingset][index][0];
         level = vc1_index_decode_table[codingset][index][1];
         lst   = index >= vc1_last_decode_table[codingset] || get_bits_left(gb) < 0;
-        if (get_bits1(gb))
-            level = -level;
+        sign  = get_bits1(gb);
     } else {
-        escape = decode210(gb);
+        int escape = decode210(gb);
         if (escape != 2) {
             index = get_vlc2(gb, ff_vc1_ac_coeff_table[codingset].table, AC_VLC_BITS, 3);
             run   = vc1_index_decode_table[codingset][index][0];
@@ -514,10 +513,8 @@ static void vc1_decode_ac_coeff(VC1Context *v, int *last, int *skip,
                 else
                     run += vc1_delta_run_table[codingset][level] + 1;
             }
-            if (get_bits1(gb))
-                level = -level;
+            sign = get_bits1(gb);
         } else {
-            int sign;
             lst = get_bits1(gb);
             if (v->s.esc3_level_length == 0) {
                 if (v->pq < 8 || v->dquantfrm) { // table 59
@@ -532,14 +529,12 @@ static void vc1_decode_ac_coeff(VC1Context *v, int *last, int *skip,
             run   = get_bits(gb, v->s.esc3_run_length);
             sign  = get_bits1(gb);
             level = get_bits(gb, v->s.esc3_level_length);
-            if (sign)
-                level = -level;
         }
     }
 
     *last  = lst;
     *skip  = run;
-    *value = level;
+    *value = (level ^ -sign) + sign;
 }
 
 /** Decode intra block in intra frames - should be faster than decode_intra_block