fix 4xm yuv->rgb565 transform

Originally committed as revision 1925 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/4xm.c

@@ -417,31 +417,37 @@ static inline void idct_put(FourXContext *f, int x, int y){
     int i;
     uint16_t *dst = ((uint16_t*)f->current_picture.data[0]) + y * stride + x;
     
-    for(i=0; i<6; i++) idct(block[i]);
+    for(i=0; i<4; i++){
+        block[i][0] += 0x80*8*8;
+        idct(block[i]);
+    }
+
+    if(!(f->avctx->flags&CODEC_FLAG_GRAY)){
+        for(i=4; i<6; i++) idct(block[i]);
+    }
 
     for(y=0; y<8; y++){
         for(x=0; x<8; x++){
             DCTELEM *temp= block[(x>>2) + 2*(y>>2)] + 2*(x&3) + 2*8*(y&3); //FIXME optimize
-            int cb= block[4][x + 8*y] + 0x80;
-            int cr= block[5][x + 8*y] + 0x80;
+            int cb= block[4][x + 8*y];
+            int cr= block[5][x + 8*y];
             int cg= (cb + cr)>>1;
             int y;
             
-            cb+=cb - 0x80;
+            cb+=cb;
             
             y = temp[0];
-            dst[0       ]= ((y+cb)>>3) + (((y+cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
+            dst[0       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
             y = temp[1];
-            dst[1       ]= ((y+cb)>>3) + (((y+cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
+            dst[1       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
             y = temp[8];
-            dst[  stride]= ((y+cb)>>3) + (((y+cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
+            dst[  stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
             y = temp[9];
-            dst[1+stride]= ((y+cb)>>3) + (((y+cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
+            dst[1+stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
             dst += 2;
         }
         dst += 2*stride - 2*8;
     }
-//    if(!(f->avctx->flags&CODEC_FLAG_GRAY)){
 }
 
 static int decode_i_mb(FourXContext *f){