add readPtr and writePtr to SkReader32 and SkWriter32

add template helper SkSWriter32, which allocates initial storage buffer
Review URL: https://codereview.appspot.com/6299075

git-svn-id: http://skia.googlecode.com/svn/trunk@4237 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 42 insertions, 1 deletions

diff --git a/include/core/SkReader32.h b/include/core/SkReader32.h
index 9e25e84a55..c127d8988c 100644
--- a/include/core/SkReader32.h
+++ b/include/core/SkReader32.h
@@ -58,7 +58,19 @@ public:
         SkASSERT(fCurr <= fStop);
         return value;
     }
-    
+
+    void* readPtr() {
+        void* ptr;
+        // we presume this "if" is resolved at compile-time
+        if (4 == sizeof(void*)) {
+            ptr = *(void**)fCurr;
+        } else {
+            memcpy(&ptr, fCurr, sizeof(void*));
+        }
+        fCurr += sizeof(void*);
+        return ptr;
+    }
+
     SkScalar readScalar() {
         SkASSERT(ptr_align_4(fCurr));
         SkScalar value = *(const SkScalar*)fCurr;
diff --git a/include/core/SkWriter32.h b/include/core/SkWriter32.h
index 9abaa467d2..793e815b3d 100644
--- a/include/core/SkWriter32.h
+++ b/include/core/SkWriter32.h
@@ -77,6 +77,17 @@ public:
         *(int32_t*)this->reserve(sizeof(value)) = value;
     }
     
+    void writePtr(void* ptr) {
+        // Since we "know" that we're always 4-byte aligned, we can tell the
+        // compiler that here, by assigning to an int32 ptr.
+        int32_t* addr = (int32_t*)this->reserve(sizeof(void*));
+        if (4 == sizeof(void*)) {
+            *(void**)addr = ptr;
+        } else {
+            memcpy(addr, &ptr, sizeof(void*));
+        }
+    }
+
     void writeScalar(SkScalar value) {
         *(SkScalar*)this->reserve(sizeof(value)) = value;
     }
@@ -176,4 +187,22 @@ private:
     Block* newBlock(size_t bytes);
 };
 
+/**
+ *  Helper class to allocated SIZE bytes as part of the writer, and to provide
+ *  that storage to the constructor as its initial storage buffer.
+ *
+ *  This wrapper ensures proper alignment rules are met for the storage.
+ */
+template <size_t SIZE> class SkSWriter32 : public SkWriter32 {
+public:
+    SkSWriter32(size_t minSize) : SkWriter32(minSize, fData.fStorage, SIZE) {}
+    
+private:
+    union {
+        void*   fPtrAlignment;
+        double  fDoubleAlignment;
+        char    fStorage[SIZE];
+    } fData;
+};
+
 #endif