Templetized SkWriter32 readTAt() & overwriteTAt()

include/core/SkWriter32.h

Index: include/core/SkWriter32.h
diff --git a/include/core/SkWriter32.h b/include/core/SkWriter32.h
index b193cbe7c407663f7a82a613b8a65b5e1e637a47..cb541749dbacded9ef80bc2279dcb3705172aa9d 100644
--- a/include/core/SkWriter32.h
+++ b/include/core/SkWriter32.h
@@ -79,9 +79,17 @@ public:
         return p;
     }
 
-    // Read or write 4 bytes at offset, which must be a multiple of 4 <= size().
-    uint32_t read32At(size_t offset) { return this->atOffset(offset); }
-    void write32At(size_t offset, uint32_t val) { this->atOffset(offset) = val; }
+    // Read/overwrite a record at offset, which must be a multiple of 4.
+    // These calls are valid only when the record was written atomically
+    // using the write* methods below.
+    template<typename T>
+    const T& readTAt(size_t offset) const {
+        return this->atOffset<T>(offset);
+    }
+    template<typename T>
+    void overwriteTAt(const T& value, size_t offset) {

[mtklein, 2014/02/10 22:37:34]

I have a slight preference for it to go back the other way, to
overwriteTAt(offset, value), just so the "At" makes a little more sense in
there.  Any reason to swap it as you have?

[f(malita), 2014/02/11 03:30:56]

Seemed more natural to follow the name hints ("overwrite <T> <at>"), but I can
see why changing the order may be confusing. I'll switch back.

+        this->atOffset<T>(offset) = value;
+    }
 
     bool writeBool(bool value) {
         this->write32(value);
@@ -238,18 +246,20 @@ public:
     }
 
 private:
-    uint32_t& atOffset(size_t offset) {
+    template<typename T>
+    T& atOffset(size_t offset) const {
         SkASSERT(SkAlign4(offset) == offset);
-        const int count = SkToInt(offset/4);
-        SkASSERT(count < fCount);
+        const int count = SkToInt(offset / 4);
+        SkASSERT(offset + sizeof(T) <= (unsigned)fCount * 4);
 
         if (count < this->externalCount()) {
-            return fExternal[count];
+            // A record should not span fExternal->fInternal.
+            SkASSERT(offset + sizeof(T) <= (unsigned)this->externalCount() * 4);
+            return *(T*)&fExternal[count];
         }
-        return fInternal[count - this->externalCount()];
+        return *(T*)&fInternal[count - this->externalCount()];
     }
 
-
     // Number of uint32_t written into fExternal.  <= fExternalLimit.
     int externalCount() const { return fCount - fInternal.count(); }