Avoid an allocation in readCharCode().

readCharCode() returns two values, and currently allocates a length-2
array on every call to do so. This change makes it instead us a
passed-in object which can be reused.

This tiny change reduces the total JS allocations done for the document
in Mozilla bug 992125 by 4.2%.

src/core/cmap.js

@@ -281,7 +281,7 @@ var CMap = (function CMapClosure() {
       return this._map;
     },
 
-    readCharCode: function(str, offset) {
+    readCharCode: function(str, offset, out) {
       var c = 0;
       var codespaceRanges = this.codespaceRanges;
       var codespaceRangesLen = this.codespaceRanges.length;
@@ -295,12 +295,14 @@ var CMap = (function CMapClosure() {
           var low = codespaceRange[k++];
           var high = codespaceRange[k++];
           if (c >= low && c <= high) {
-            return [c, n + 1];
+            out.charcode = c;
+            out.length = n + 1;
+            return;
           }
         }
       }
-
+      out.charcode = 0;
-      return [0, 1];
+      out.length = 1;
     }
   };
   return CMap;

src/core/fonts.js

@@ -4574,10 +4574,11 @@ var Font = (function FontClosure() {
       if (this.cMap) {
         // composite fonts have multi-byte strings convert the string from
         // single-byte to multi-byte
+        var c = {};
         while (i < chars.length) {
-          var c = this.cMap.readCharCode(chars, i);
+          this.cMap.readCharCode(chars, i, c);
-          charcode = c[0];
+          charcode = c.charcode;
-          var length = c[1];
+          var length = c.length;
           i += length;
           glyph = this.charToGlyph(charcode);
           glyphs.push(glyph);

test/unit/cmap_spec.js

@@ -65,12 +65,13 @@ describe('cmap', function() {
               'endcodespacerange\n';
     var stream = new StringStream(str);
     var cmap = CMapFactory.create(stream);
-    var c = cmap.readCharCode(String.fromCharCode(1), 0);
+    var c = {};
-    expect(c[0]).toEqual(1);
+    cmap.readCharCode(String.fromCharCode(1), 0, c);
-    expect(c[1]).toEqual(1);
+    expect(c.charcode).toEqual(1);
-    c = cmap.readCharCode(String.fromCharCode(0, 0, 0, 3), 0);
+    expect(c.length).toEqual(1);
-    expect(c[0]).toEqual(3);
+    cmap.readCharCode(String.fromCharCode(0, 0, 0, 3), 0, c);
-    expect(c[1]).toEqual(4);
+    expect(c.charcode).toEqual(3);
+    expect(c.length).toEqual(4);
   });
   it('decodes 4 byte codespace ranges', function() {
     var str = '1 begincodespacerange\n' +
@@ -78,9 +79,10 @@ describe('cmap', function() {
               'endcodespacerange\n';
     var stream = new StringStream(str);
     var cmap = CMapFactory.create(stream);
-    var c = cmap.readCharCode(String.fromCharCode(0x8E, 0xA1, 0xA1, 0xA1), 0);
+    var c = {};
-    expect(c[0]).toEqual(0x8EA1A1A1);
+    cmap.readCharCode(String.fromCharCode(0x8E, 0xA1, 0xA1, 0xA1), 0, c);
-    expect(c[1]).toEqual(4);
+    expect(c.charcode).toEqual(0x8EA1A1A1);
+    expect(c.length).toEqual(4);
   });
   it('read usecmap', function() {
     var str = '/Adobe-Japan1-1 usecmap\n';