SkBlockMemoryStream implements peek()

src/core/SkStream.cpp

Index: src/core/SkStream.cpp
diff --git a/src/core/SkStream.cpp b/src/core/SkStream.cpp
index ad67a0ba7db43759c8c6f9e03ff2f25bc0ac43ca..ff96db7500a255d3c35405ad30a549c78a17c5b4 100644
--- a/src/core/SkStream.cpp
+++ b/src/core/SkStream.cpp
@@ -724,6 +724,30 @@ public:
         return fOffset == fSize;
     }
 
+    bool peek(void* buff, size_t size) const override {
+        SkASSERT(buff != NULL);
+        if (fOffset + size > fSize) {
+            return false;
+        }
+        char* buffer = static_cast<char*>(buff);
+        const SkDynamicMemoryWStream::Block* current = fCurrent;

[scroggo, 2015/05/21 14:13:18]

Patch set 2 separates out the code for dealing with the current block from the
code that deals with the rest. AFAICT, this means we skip the following
(unnecessary) calculations for all loop iterations but the first (which
technically is no longer an iteration of the loop):

- subtract 0
- add 0
- assign 0 to a variable (this is removed from the first as well)

On the other hand, we have some mostly duplicated code. Unless the original code
is noticeably slower, I'd prefer less duplication.

[hal.canary, 2015/05/21 14:35:47]

reverted

+        size_t bytesFromCurrent =
+            SkTMin(current->written() - fCurrentOffset, size);
+        memcpy(buffer, current->start() + fCurrentOffset, bytesFromCurrent);
+        size -= bytesFromCurrent;
+        buffer += bytesFromCurrent;
+        current = current->fNext;
+        while (size) {
+            SkASSERT(current);
+            bytesFromCurrent = SkTMin(current->written(), size);
+            memcpy(buffer, current->start(), bytesFromCurrent);
+            size -= bytesFromCurrent;
+            buffer += bytesFromCurrent;
+            current = current->fNext;
+        }
+        return true;
+    }
+
     bool rewind() override {
         fCurrent = fBlockMemory->fHead;
         fOffset = 0;