Simplify stereo rematrixing by only using one temporary variable. It is also

about 1.8% faster on my system.

Originally committed as revision 20090 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -604,7 +604,6 @@ static void do_rematrixing(AC3DecodeContext *s)
 {
     int bnd, i;
     int end, bndend;
-    int tmp0, tmp1;
 
     end = FFMIN(s->end_freq[1], s->end_freq[2]);
 
@@ -613,10 +612,9 @@ static void do_rematrixing(AC3DecodeContext *s)
         if(s->rematrixing_flags[bnd]) {
             bndend = FFMIN(end, ff_ac3_rematrix_band_tab[bnd+1]);
             for(; i<bndend; i++) {
-                tmp0 = s->fixed_coeffs[1][i];
-                tmp1 = s->fixed_coeffs[2][i];
-                s->fixed_coeffs[1][i] = tmp0 + tmp1;
-                s->fixed_coeffs[2][i] = tmp0 - tmp1;
+                int tmp0 = s->fixed_coeffs[1][i];
+                s->fixed_coeffs[1][i] -= s->fixed_coeffs[2][i];
+                s->fixed_coeffs[2][i]  = tmp0 - s->fixed_coeffs[2][i];
             }
         }
     }