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

3 files changed, 74 insertions, 5 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
diff --git a/tests/Writer32Test.cpp b/tests/Writer32Test.cpp
index 35fb29f38e..311f37d8fb 100644
--- a/tests/Writer32Test.cpp
+++ b/tests/Writer32Test.cpp
@@ -12,6 +12,34 @@
 #include "SkWriter32.h"
 #include "Test.h"
 
+static void test_ptr(skiatest::Reporter* reporter) {
+    SkSWriter32<32> writer(32);
+    
+    void* p0 = reporter;
+    void* p1 = &writer;
+
+    // try writing ptrs where at least one of them may be at a non-multiple of
+    // 8 boundary, to confirm this works on 64bit machines.
+
+    writer.writePtr(p0);
+    writer.write8(0x33);
+    writer.writePtr(p1);
+    writer.write8(0x66);
+
+    size_t size = writer.size();
+    REPORTER_ASSERT(reporter, 2 * sizeof(void*) + 2 * sizeof(int32_t));
+
+    char buffer[32];
+    SkASSERT(sizeof(buffer) >= size);
+    writer.flatten(buffer);
+
+    SkReader32 reader(buffer, size);
+    REPORTER_ASSERT(reporter, reader.readPtr() == p0);
+    REPORTER_ASSERT(reporter, reader.readInt() == 0x33);
+    REPORTER_ASSERT(reporter, reader.readPtr() == p1);
+    REPORTER_ASSERT(reporter, reader.readInt() == 0x66);
+}
+
 static void test1(skiatest::Reporter* reporter, SkWriter32* writer) {
     const uint32_t data[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
     for (size_t i = 0; i < SK_ARRAY_COUNT(data); ++i) {
@@ -79,8 +107,7 @@ static void Tests(skiatest::Reporter* reporter) {
     
     // small storage
     {
-        intptr_t storage[8];
-        SkWriter32 writer(100, storage, sizeof(storage));
+        SkSWriter32<8 * sizeof(intptr_t)> writer(100);
         test1(reporter, &writer);
         writer.reset(); // should just rewind our storage
         test2(reporter, &writer);
@@ -88,12 +115,13 @@ static void Tests(skiatest::Reporter* reporter) {
     
     // large storage
     {
-        intptr_t storage[1024];
-        SkWriter32 writer(100, storage, sizeof(storage));
+        SkSWriter32<1024 * sizeof(intptr_t)> writer(100);
         test1(reporter, &writer);
         writer.reset(); // should just rewind our storage
         test2(reporter, &writer);
     }
+    
+    test_ptr(reporter);
 }
 
 #include "TestClassDef.h"