Refactor JavaScript support for packed boolean arrays

mojo/public/js/bindings/codec.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 define("mojo/public/js/bindings/codec", [
   "mojo/public/js/bindings/unicode",
   "mojo/public/js/bindings/buffer"
   ], function(unicode, buffer) {
 
   var kErrorUnsigned = "Passing negative value to unsigned";
@@ skipping 117 matching lines @@
     var base = this.next;
     this.next += numberOfElements;
     return unicode.decodeUtf8String(
         new Uint8Array(this.buffer.arrayBuffer, base, numberOfElements));
   };
 
   Decoder.prototype.decodeArray = function(cls) {
     var numberOfBytes = this.readUint32();
     var numberOfElements = this.readUint32();
     var val = new Array(numberOfElements);
-    for (var i = 0; i < numberOfElements; ++i) {
-      val[i] = cls.decode(this);
+    if (cls.cls === PackedBool) {
+      var byte;
+      for (var i = 0; i < numberOfElements; ++i) {
+        if (i % 8 === 0)
+          byte = this.readUint8();
+        val[i] = (byte & (1 << i % 8)) ? true : false;
+      }
+    } else {
+      for (var i = 0; i < numberOfElements; ++i) {
+        val[i] = cls.decode(this);
+      }
     }
     return val;
   };
-
-  Decoder.prototype.decodeBoolArray = function() {
-    var numberOfBytes = this.readUint32();
-    var numberOfElements = this.readUint32();
-
-    var val = new Array(numberOfElements);
-    var byte;
-    for (var i = 0; i < numberOfElements; ++i) {
-        if (i % 8 === 0)
-            byte = this.readUint8();
-        val[i] = (byte & (1 << i % 8)) ? true : false;
-    }
-    return val;
-  };
 
   Decoder.prototype.decodeStruct = function(cls) {
     return cls.decode(this);
   };
 
   Decoder.prototype.decodeStructPointer = function(cls) {
     var pointer = this.decodePointer();
     if (!pointer) {
       return null;
     }
     return cls.decode(this.decodeAndCreateDecoder(pointer));
   };
 
   Decoder.prototype.decodeArrayPointer = function(cls) {
     var pointer = this.decodePointer();
     if (!pointer) {
       return null;
     }
     return this.decodeAndCreateDecoder(pointer).decodeArray(cls);
   };
 
-  Decoder.prototype.decodeBoolArrayPointer = function() {
-    var pointer = this.decodePointer();
-    if (!pointer) {
-      return null;
-    }
-    return this.decodeAndCreateDecoder(pointer).decodeBoolArray();
-  };
-
   Decoder.prototype.decodeStringPointer = function() {
     var pointer = this.decodePointer();
     if (!pointer) {
       return null;
     }
     return this.decodeAndCreateDecoder(pointer).decodeString();
   };
 
   // Encoder ------------------------------------------------------------------
 
@@ skipping 93 matching lines @@
   Encoder.prototype.encodeString = function(val) {
     var base = this.next + kArrayHeaderSize;
     var numberOfElements = unicode.encodeUtf8String(
         val, new Uint8Array(this.buffer.arrayBuffer, base));
     var numberOfBytes = kArrayHeaderSize + numberOfElements;
     this.writeUint32(numberOfBytes);
     this.writeUint32(numberOfElements);
     this.next += numberOfElements;
   };
 
-  Encoder.prototype.encodeArray = function(cls, val, numberOfElements) {
+  Encoder.prototype.encodeArray =
+      function(cls, val, numberOfElements, encodedSize) {
     if (numberOfElements === undefined)
       numberOfElements = val.length;
-    var numberOfBytes = kArrayHeaderSize + cls.encodedSize * val.length;
-    this.writeUint32(numberOfBytes);
+    if (encodedSize === undefined)
+      encodedSize = kArrayHeaderSize + cls.encodedSize * numberOfElements;
+
+    this.writeUint32(encodedSize);
     this.writeUint32(numberOfElements);
-    for (var i = 0; i < val.length; ++i) {
-      cls.encode(this, val[i]);
+
+    if (cls.cls === PackedBool) {
+      var byte = 0;
+      var i = 0;
+      for (; i < numberOfElements; ++i) {
+        if (i > 0 && i % 8 === 0) {

[Matt Perry, 2014/08/11 21:24:32]

alternative: move this if to the end of the for statement, change it to

if (i % 8 === 7 || i == numberOfElements-1)

and remove the post-for if statement below?

[hansmuller, 2014/08/11 21:43:48]

Excellent suggestion, that's much simpler.

+          Uint8.encode(this, byte);
+          byte = 0;
+        }
+        if (val[i])
+          byte |= (1 << i % 8);
+      }
+      if (i > 0 && (i - 1) % 8 != 0)
+        Uint8.encode(this, byte);
+    } else {
+      for (var i = 0; i < numberOfElements; ++i)
+        cls.encode(this, val[i]);
     }
   };
 
   Encoder.prototype.encodeStruct = function(cls, val) {
     return cls.encode(this, val);
   };
 
   Encoder.prototype.encodeStructPointer = function(cls, val) {
     if (!val) {
       this.encodePointer(val);
       return;
     }
     var encoder = this.createAndEncodeEncoder(cls.encodedSize);
     cls.encode(encoder, val);
   };
 
   Encoder.prototype.encodeArrayPointer = function(cls, val) {
     if (!val) {
       this.encodePointer(val);
       return;
     }
-    var encodedSize = kArrayHeaderSize + cls.encodedSize * val.length;
-    var encoder = this.createAndEncodeEncoder(encodedSize);
-    encoder.encodeArray(cls, val);
-  };
-
-  Encoder.prototype.encodeBoolArrayPointer = function(val) {
-    if (!val) {
-      this.encodePointer(val);
-      return;
-    }
     var numberOfElements = val.length;
-    var encodedSize = kArrayHeaderSize + Math.ceil(numberOfElements / 8);
+    var encodedSize = kArrayHeaderSize + ((cls.cls === PackedBool) ?
+        Math.ceil(numberOfElements / 8) : cls.encodedSize * numberOfElements);
     var encoder = this.createAndEncodeEncoder(encodedSize);
-
-    var bits = new Uint8Array(Math.ceil(numberOfElements / 8));
-    for (var i = 0; i < numberOfElements; i++) {
-        if (val[i])
-            bits[Math.floor(i / 8)] |= (1 << i % 8);
-    }
-    encoder.encodeArray(Uint8, bits, numberOfElements);
+    encoder.encodeArray(cls, val, numberOfElements, encodedSize);
   };
 
   Encoder.prototype.encodeStringPointer = function(val) {
     if (!val) {
       this.encodePointer(val);
       return;
     }
     var encodedSize = kArrayHeaderSize + unicode.utf8Length(val);
     var encoder = this.createAndEncodeEncoder(encodedSize);
     encoder.encodeString(val);
@@ skipping 110 matching lines @@
       this.requestID = this.decoder.readUint64();
     this.decoder.skip(messageHeaderSize - this.decoder.next);
   }
 
   MessageReader.prototype.decodeStruct = function(cls) {
     return cls.decode(this.decoder);
   };
 
   // Built-in types -----------------------------------------------------------
 
+  // This type is only used with ArrayOf(PackedBool).
+  function PackedBool() {
+  }
+
   function Int8() {
   }
 
   Int8.encodedSize = 1;
 
   Int8.decode = function(decoder) {
     return decoder.readInt8();
   };
 
   Int8.encode = function(encoder, val) {
@@ skipping 165 matching lines @@
   ArrayOf.prototype.encodedSize = 8;
 
   ArrayOf.prototype.decode = function(decoder) {
     return decoder.decodeArrayPointer(this.cls);
   };
 
   ArrayOf.prototype.encode = function(encoder, val) {
     encoder.encodeArrayPointer(this.cls, val);
   };
 
-  function ArrayOfBoolArrayPointers() {
-  }
-
-  ArrayOfBoolArrayPointers.prototype.encodedSize = 8;
-
-  ArrayOfBoolArrayPointers.prototype.decode = function(decoder) {
-    return decoder.decodeBoolArrayPointer();
-  };
-
-  ArrayOfBoolArrayPointers.prototype.encode = function(encoder, val) {
-    encoder.encodeBoolArrayPointer(val);
-  };
-
   function Handle() {
   }
 
   Handle.encodedSize = 4;
 
   Handle.decode = function(decoder) {
     return decoder.decodeHandle();
   };
 
   Handle.encode = function(encoder, val) {
@@ skipping 19 matching lines @@
   exports.Uint16 = Uint16;
   exports.Int32 = Int32;
   exports.Uint32 = Uint32;
   exports.Int64 = Int64;
   exports.Uint64 = Uint64;
   exports.Float = Float;
   exports.Double = Double;
   exports.String = String;
   exports.PointerTo = PointerTo;
   exports.ArrayOf = ArrayOf;
-  exports.ArrayOfBoolArrayPointers = ArrayOfBoolArrayPointers;
+  exports.PackedBool = PackedBool;
   exports.Handle = Handle;
   return exports;
 });