optimize quantizaton (about 3x faster)

further opt is easily possible but could lead to overflows depening upon coefficient range, so this wont be done yet as it would make the code somewhat less flexible

Originally committed as revision 3354 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/snow.c

@@ -1801,29 +1801,33 @@ static void quantize(SnowContext *s, SubBand *b, DWTELEM *src, int stride, int b
     const int h= b->height;
     const int qlog= clip(s->qlog + b->qlog, 0, 128);
     const int qmul= qexp[qlog&7]<<(qlog>>3);
-    int x,y;
+    int x,y, thres1, thres2;
+    START_TIMER
 
     assert(QROOT==8);
 
     bias= bias ? 0 : (3*qmul)>>3;
+    thres1= ((qmul - bias)>>QEXPSHIFT) - 1;
+    thres2= 2*thres1;
     
     if(!bias){
         for(y=0; y<h; y++){
             for(x=0; x<w; x++){
-                int i= src[x + y*stride]; 
-                //FIXME use threshold
-                //FIXME optimize
-                //FIXME bias
-                if(i>=0){
-                    i<<= QEXPSHIFT;
-                    i/= qmul;
-                    src[x + y*stride]=  i;
-                }else{
-                    i= -i;
-                    i<<= QEXPSHIFT;
-                    i/= qmul;
-                    src[x + y*stride]= -i;
-                }
+                int i= src[x + y*stride];
+                
+                if((unsigned)(i+thres1) > thres2){
+                    if(i>=0){
+                        i<<= QEXPSHIFT;
+                        i/= qmul; //FIXME optimize
+                        src[x + y*stride]=  i;
+                    }else{
+                        i= -i;
+                        i<<= QEXPSHIFT;
+                        i/= qmul; //FIXME optimize
+                        src[x + y*stride]= -i;
+                    }
+                }else
+                    src[x + y*stride]= 0;
             }
         }
     }else{
@@ -1831,22 +1835,25 @@ static void quantize(SnowContext *s, SubBand *b, DWTELEM *src, int stride, int b
             for(x=0; x<w; x++){
                 int i= src[x + y*stride]; 
                 
-                //FIXME use threshold
-                //FIXME optimize
-                //FIXME bias
-                if(i>=0){
-                    i<<= QEXPSHIFT;
-                    i= (i + bias) / qmul;
-                    src[x + y*stride]=  i;
-                }else{
-                    i= -i;
-                    i<<= QEXPSHIFT;
-                    i= (i + bias) / qmul;
-                    src[x + y*stride]= -i;
-                }
+                if((unsigned)(i+thres1) > thres2){
+                    if(i>=0){
+                        i<<= QEXPSHIFT;
+                        i= (i + bias) / qmul; //FIXME optimize
+                        src[x + y*stride]=  i;
+                    }else{
+                        i= -i;
+                        i<<= QEXPSHIFT;
+                        i= (i + bias) / qmul; //FIXME optimize
+                        src[x + y*stride]= -i;
+                    }
+                }else
+                    src[x + y*stride]= 0;
             }
         }
     }
+    if(level+1 == s->spatial_decomposition_count){
+//        STOP_TIMER("quantize")
+    }
 }
 
 static void dequantize(SnowContext *s, SubBand *b, DWTELEM *src, int stride){