Templetized SkWriter32 readTAt() & overwriteTAt()

src/core/SkWriter32.cpp

Index: src/core/SkWriter32.cpp
diff --git a/src/core/SkWriter32.cpp b/src/core/SkWriter32.cpp
index 5e89ed655b70e5d83da4df2588704689898b52e6..cb8506882780a7df172f6af71cc01ba2c0c7115a 100644
--- a/src/core/SkWriter32.cpp
+++ b/src/core/SkWriter32.cpp
@@ -44,15 +44,19 @@ void SkWriter32::writeString(const char str[], size_t len) {
     if ((long)len < 0) {
         len = strlen(str);
     }
-    this->write32(len);
+
     // add 1 since we also write a terminating 0

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

Hmm, maybe we can make this clearer?  Does this work?

// [ 4 byte len ] [ str ... ] [1-4 \0s]
uint32_t* ptr = this->reservePad(sizeof(uint32_t) + len + 1);
ptr[0] = len;
memcpy(ptr+1, str, len);

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

Ah, reservePad takes care of padding, doesn't it. Except its padding doesn't
look quite as efficient as the one-write trick below, but we can fix that.

     size_t alignedLen = SkAlign4(len + 1);
-    char* ptr = (char*)this->reserve(alignedLen);
+    // reserve an additional 4 bytes for len storage
+    uint32_t* lenPtr = this->reserve(alignedLen + sizeof(uint32_t));
+    char* ptr = (char*)(lenPtr + 1);
     {
         // Write the terminating 0 and fill in the rest with zeroes
         uint32_t* padding = (uint32_t*)(ptr + (alignedLen - 4));
         *padding = 0;
     }
+
+    *lenPtr = len;
     // Copy the string itself.
     memcpy(ptr, str, len);
 }