JBIG2 20% faster SimpleSegmentVisitor_drawBitmap

Moved the switch(combinationOperator) outside the width and height loops
Check bitmap[i][j] before applying the switch(combinationOperator)

src/core/jbig2.js

@@ -938,35 +938,43 @@ var Jbig2Image = (function Jbig2ImageClosure() {
       var combinationOperator = pageInfo.combinationOperatorOverride ?
         regionInfo.combinationOperator : pageInfo.combinationOperator;
       var buffer = this.buffer;
+      switch (combinationOperator) {
+        case 0: // OR
           for (var i = 0; i < height; i++) {
             var mask = 128 >> (regionInfo.x & 7);
             var offset = (i + regionInfo.y) * rowSize + (regionInfo.x >> 3);
-        switch (combinationOperator) {
-          case 0: // OR
             for (var j = 0; j < width; j++) {
-              buffer[offset] |= bitmap[i][j] ? mask : 0;
+              if (bitmap[i][j]) {
+                buffer[offset] |= mask;
+              }
               mask >>= 1;
               if (!mask) {
                 mask = 128;
                 offset++;
               }
             }
+          }
         break;
         case 2: // XOR
+          for (var i = 0; i < height; i++) {
+            var mask = 128 >> (regionInfo.x & 7);
+            var offset = (i + regionInfo.y) * rowSize + (regionInfo.x >> 3);
             for (var j = 0; j < width; j++) {
-              buffer[offset] ^= bitmap[i][j] ? mask : 0;
+              if (bitmap[i][j]) {
+                buffer[offset] ^= mask;
+              }
               mask >>= 1;
               if (!mask) {
                 mask = 128;
                 offset++;
               }
             }
+          }
           break;
         default:
           error('JBIG2 error: operator ' + combinationOperator +
                 ' is not supported');
       }
-      }
     },
     onImmediateGenericRegion:
       function SimpleSegmentVisitor_onImmediateGenericRegion(region, data,