Implement pack option

Fixes #2.
Closes #21.

Squashed commit of the following:

commit 093212b
Author: Lee, SungUk <sulee@ea.com>
Date:   Wed Aug 3 10:33:09 2016 +0900

    Change Struct's second argument type to object

    Applied review comments;
    - Constructor arugments type change boolean to object
    - Assign of `StructType.isPacked` use ternary operator
    - Remove `usePack` method
    - `sizeof` and `alignof` calculation move to C++ code

commit a1e8f66
Author: Lee, SungUk <sulee@ea.com>
Date:   Tue Jan 5 15:11:11 2016 +0900

    Fix broken unittests of appveyor

commit d5415f3
Author: Lee, SungUk <sulee@ea.com>
Date:   Tue Jan 5 13:15:27 2016 +0900

    Resolve #2 Implement `usePack`

    - Apply [Alexander Seliverstov's method][1]
    - Now, `Struct` use 2nd arguments
    - `usePack()` switch padding mode

    [1]: https://groups.google.com/d/msg/nodejs/2wKCYmGPT5E/DLi4Pjt7j_4J

Author: d3m3vilurr

lib/struct.js

@@ -117,10 +117,12 @@ function Struct () {
   StructType.toString = toString
   StructType.fields = {}
 
+  var opt = (arguments.length > 0 && arguments[1]) ? arguments[1] : {};
   // Setup the ref "type" interface. The constructor doubles as the "type" object
   StructType.size = 0
   StructType.alignment = 0
   StructType.indirection = 1
+  StructType.isPacked = opt.packed ? Boolean(opt.packed) : false
   StructType.get = get
   StructType.set = set
 
@@ -245,7 +247,11 @@ function recalc (struct) {
     if (type.indirection > 1) {
       alignment = ref.alignof.pointer
     }
-    struct.alignment = Math.max(struct.alignment, alignment)
+    if (struct.isPacked) {
+      struct.alignment = Math.min(struct.alignment || alignment, alignment)
+    } else {
+      struct.alignment = Math.max(struct.alignment, alignment)
+    }
   })
 
   // second loop through sets the `offset` property on each "field"
@@ -270,12 +276,14 @@ function recalc (struct) {
   function addType (type) {
     var offset = struct.size
     var align = type.indirection === 1 ? type.alignment : ref.alignof.pointer
-    var padding = (align - (offset % align)) % align
+    var padding = struct.isPacked ? 0 : (align - (offset % align)) % align
     var size = type.indirection === 1 ? type.size : ref.sizeof.pointer
 
     offset += padding
 
-    assert.equal(offset % align, 0, "offset should align")
+    if (!struct.isPacked) {
+      assert.equal(offset % align, 0, "offset should align")
+    }
 
     // adjust the "size" of the struct type
     struct.size = offset + size

test/struct.js

@@ -379,4 +379,18 @@ describe('Struct', function () {
 
   })
 
+  describe('packed struct', function () {
+
+    it('with-padding/no-padding struct', function () {
+      var np = Struct({ a: 'char', p: ref.refType('void') }, {packed: true})
+      assert.equal(bindings['test20 sizeof'], np.size)
+      assert.equal(bindings['test20 alignof'], np.alignment)
+
+      var wp = Struct({ a: 'char', p: ref.refType('void') })
+      assert.equal(bindings['test21 sizeof'], wp.size)
+      assert.equal(bindings['test21 alignof'], wp.alignment)
+    })
+
+  })
+
 })

test/struct_tests.cc

@@ -145,6 +145,18 @@ typedef struct _test19 {
                           in an album or playlist struct */
 } test19;
 
+#pragma pack(1)
+typedef struct _test20 {
+  char a;
+  void *p;
+} test20;
+
+#pragma pack()
+typedef struct _test21 {
+  char a;
+  void *p;
+} test21;
+
 void Initialize(v8::Handle<v8::Object> target) {
   Nan::HandleScope scope;
 
@@ -275,6 +287,11 @@ void Initialize(v8::Handle<v8::Object> target) {
   target->Set(Nan::New<v8::String>("test19 offsetof popularity").ToLocalChecked(), Nan::New<v8::Number>(offsetof(test19, popularity)));
   target->Set(Nan::New<v8::String>("test19 offsetof next").ToLocalChecked(), Nan::New<v8::Number>(offsetof(test19, next)));
 
+  target->Set(Nan::New<v8::String>("test20 sizeof").ToLocalChecked(), Nan::New<v8::Number>(sizeof(test20)));
+  target->Set(Nan::New<v8::String>("test20 alignof").ToLocalChecked(), Nan::New<v8::Number>(__alignof__(test20)));
+
+  target->Set(Nan::New<v8::String>("test21 sizeof").ToLocalChecked(), Nan::New<v8::Number>(sizeof(test21)));
+  target->Set(Nan::New<v8::String>("test21 alignof").ToLocalChecked(), Nan::New<v8::Number>(__alignof__(test21)));
 }
 
 } // anonymous namespace