Minimize memory usage of font-related arrays.

This patch replaces some vanilla arrays with typed arrays, and avoids
some array copying.

It reduces the peak RSS when viewing
http://www.dynacw.co.jp/Portals/3/fontsamplepdf/sample_4942546800828.pdf
from ~940 MiB to ~750 MiB, and reduces its load time from 83 to 76 ms.

src/core/fonts.js

@@ -2433,17 +2433,43 @@ var Font = (function FontClosure() {
     // length
     var length = data.length;
 
-    // Per spec tables must be 4-bytes align so add padding as needed
+    // Per spec tables must be 4-bytes align so add padding as needed.
-    while (data.length & 3) {
+    var paddedLength = length;
-      data.push(0x00);
+    while (paddedLength & 3) {
+      paddedLength++;
     }
+    var i;
+    var padding = paddedLength - length;
+    if (padding !== 0) {
+      // Padding is required. |data| can be an Array, Uint8Array, or
+      // Uint16Array. In the latter two cases we need to create slightly larger
+      // typed arrays and copy the old contents in. Fortunately that's not a
+      // common case.
+      var data2;
+      if (data instanceof Array) {
+        for (i = 0; i < padding; i++) {
+          data.push(0);
+        }
+      } else if (data instanceof Uint8Array) {
+        data2 = new Uint8Array(paddedLength);
+        data2.set(data);
+        data = data2;
+      } else if (data instanceof Uint16Array) {
+        data2 = new Uint16Array(paddedLength);
+        data2.set(data);
+        data = data2;
+      } else {
+        error('bad array kind in createTableEntry');
+      }
+    }
+
     while (file.virtualOffset & 3) {
       file.virtualOffset++;
     }
 
     // checksum
     var checksum = 0, n = data.length;
-    for (var i = 0; i < n; i += 4) {
+    for (i = 0; i < n; i += 4) {
       checksum = (checksum + int32(data[i], data[i + 1], data[i + 2],
                                    data[i + 3])) | 0;
     }
@@ -2452,6 +2478,8 @@ var Font = (function FontClosure() {
                       string32(offset) + string32(length));
     file.file += tableEntry;
     file.virtualOffset += data.length;
+
+    return data;
   }
 
   function isTrueTypeFile(file) {
@@ -4066,13 +4094,7 @@ var Font = (function FontClosure() {
       // rewrite the tables but tweak offsets
       for (i = 0; i < numTables; i++) {
         table = tables[tablesNames[i]];
-        var data = [];
+        table.data = createTableEntry(ttf, table.tag, table.data);
-
-        tableData = table.data;
-        for (var j = 0, jj = tableData.length; j < jj; j++) {
-          data.push(tableData[j]);
-        }
-        createTableEntry(ttf, table.tag, data);
       }
 
       // Add the table datas
@@ -4254,7 +4276,7 @@ var Font = (function FontClosure() {
 
       var field;
       for (field in fields) {
-        createTableEntry(otf, field, fields[field]);
+        fields[field] = createTableEntry(otf, field, fields[field]);
       }
       for (field in fields) {
         var table = fields[field];

src/shared/util.js

@@ -436,7 +436,7 @@ function bytesToString(bytes) {
 
 function stringToArray(str) {
   var length = str.length;
-  var array = [];
+  var array = new Uint16Array(length);
   for (var i = 0; i < length; ++i) {
     array[i] = str.charCodeAt(i);
   }