Pickle::Write* micro-optimizations

base/pickle.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_PICKLE_H__
 #define BASE_PICKLE_H__
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 198 matching lines @@
   }
 
   // Methods for adding to the payload of the Pickle.  These values are
   // appended to the end of the Pickle's payload.  When reading values from a
   // Pickle, it is important to read them in the order in which they were added
   // to the Pickle.
   bool WriteBool(bool value) {
     return WriteInt(value ? 1 : 0);
   }
   bool WriteInt(int value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   // WARNING: DO NOT USE THIS METHOD IF PICKLES ARE PERSISTED IN ANY WAY.
   // It will write whatever a "long" is on this architecture. On 32-bit
   // platforms, it is 32 bits. On 64-bit platforms, it is 64 bits. If persisted
   // pickles are still around after upgrading to 64-bit, or if they are copied
   // between dissimilar systems, YOUR PICKLES WILL HAVE GONE BAD.
   bool WriteLongUsingDangerousNonPortableLessPersistableForm(long value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteUInt16(uint16 value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteUInt32(uint32 value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteInt64(int64 value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteUInt64(uint64 value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteFloat(float value) {
-    return WriteBytes(&value, sizeof(value));
+    return WritePOD(value);
   }
   bool WriteString(const std::string& value);
   bool WriteWString(const std::wstring& value);
   bool WriteString16(const string16& value);
   // "Data" is a blob with a length. When you read it out you will be given the
   // length. See also WriteBytes.
   bool WriteData(const char* data, int length);
-  // "Bytes" is a blob with no length. The caller must specify the lenght both
+  // "Bytes" is a blob with no length. The caller must specify the length both
   // when reading and writing. It is normally used to serialize PoD types of a
   // known size. See also WriteData.
-  bool WriteBytes(const void* data, int data_len);
+  bool WriteBytes(const void* data, int length);
 
   // Reserves space for upcoming writes when multiple writes will be made and
   // their sizes are computed in advance. It can be significantly faster to call
   // Reserve() before calling WriteFoo() multiple times.
   void Reserve(size_t additional_capacity);
 
   // Payload follows after allocation of Header (header size is customizable).
   struct Header {
     uint32 payload_size;  // Specifies the size of the payload.
   };
@@ skipping 28 matching lines @@
 
  protected:
   char* mutable_payload() {
     return reinterpret_cast<char*>(header_) + header_size_;
   }
 
   size_t capacity() const {
     return capacity_;
   }
 
-  // Resizes the buffer for use when writing the specified amount of data. The
-  // location that the data should be written at is returned, or NULL if there
-  // was an error. Call EndWrite with the returned offset and the given length
-  // to pad out for the next write.
-  char* BeginWrite(size_t length);
-
-  // Completes the write operation by padding the data with NULL bytes until it
-  // is padded. Should be paired with BeginWrite, but it does not necessarily
-  // have to be called after the data is written.
-  void EndWrite(char* dest, int length);
-
-  // Resize the capacity, note that the input value should include the size of
-  // the header: new_capacity = sizeof(Header) + desired_payload_capacity.
-  // A realloc() failure will cause a Resize failure... and caller should check
-  // the return result for true (i.e., successful resizing).
-  bool Resize(size_t new_capacity);
+  // Resize the capacity, note that the input value should not include the size
+  // of the header.
+  void Resize(size_t new_capacity);
 
   // Aligns 'i' by rounding it up to the next multiple of 'alignment'
   static size_t AlignInt(size_t i, int alignment) {
     return i + (alignment - (i % alignment)) % alignment;
   }
 
   // Find the end of the pickled data that starts at range_start.  Returns NULL
   // if the entire Pickle is not found in the given data range.
   static const char* FindNext(size_t header_size,
                               const char* range_start,
                               const char* range_end);
 
   // The allocation granularity of the payload.
   static const int kPayloadUnit;
 
  private:
   friend class PickleIterator;
 
   Header* header_;
   size_t header_size_;  // Supports extra data between header and payload.
-  // Allocation size of payload (or -1 if allocation is const).
+  // Allocation size of payload (or -1 if allocation is const). Note: this
+  // doesn't count the header.
   size_t capacity_;

[jar (doing other things), 2013/10/29 16:50:48]

How about changing this name to:
capacity_after_header_

[piman, 2013/10/30 20:29:06]

Done.

+  // The offset at which we will write the next field. Note: this doesn't count
+  // the header.
+  size_t write_offset_;
+
+  // Just like WriteBytes, but with a compile-time size, for performance.
+  template<size_t length> void WriteBytesStatic(const void* data);
+
+  // Writes a POD by copying its bytes.
+  template <typename T> bool WritePOD(const T& data) {
+    WriteBytesStatic<sizeof(data)>(&data);
+    return true;
+  }
+  inline void WriteBytesCommon(const void* data, size_t length);
 
   FRIEND_TEST_ALL_PREFIXES(PickleTest, Resize);
   FRIEND_TEST_ALL_PREFIXES(PickleTest, FindNext);
   FRIEND_TEST_ALL_PREFIXES(PickleTest, FindNextWithIncompleteHeader);
 };
 
 #endif  // BASE_PICKLE_H__