diff --git a/ChangeLog b/ChangeLog
index 77dcdee8..f34a6cff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -24,6 +24,11 @@
 
 	* src/SendMessageQueue.cc (cancelAllRequest): Fixed.
 
+	* src/Util.cc (isPowerOf): New function.
+	* src/Util.h (isPowerOf): New function.
+	* src/PeerMessageUtil.cc (checkLength): Added a check for length
+	whether or not it is power of 2.
+	
 2006-03-28  Tatsuhiro Tsujikawa  <tujikawa at rednoah dot com>
 
 	Added new class SendMessageQueue that includes PendingMessages and
diff --git a/src/CookieBox.cc b/src/CookieBox.cc
index 1371afb0..85e58613 100644
--- a/src/CookieBox.cc
+++ b/src/CookieBox.cc
@@ -30,13 +30,13 @@ void CookieBox::add(const Cookie& cookie) {
   cookies.push_back(cookie);
 }
 
-void CookieBox::add(string cookieStr) {
+void CookieBox::add(const string& cookieStr) {
   Cookie c;
   parse(c, cookieStr);
   cookies.push_back(c);
 }
 
-void CookieBox::setField(Cookie& cookie, string name, string value) const {
+void CookieBox::setField(Cookie& cookie, const string& name, const string& value) const {
   if(name.size() == string("secure").size() &&
      strcasecmp(name.c_str(), "secure") == 0) {
     cookie.secure = true;
@@ -52,7 +52,7 @@ void CookieBox::setField(Cookie& cookie, string name, string value) const {
   }
 }
 
-void CookieBox::parse(Cookie& cookie, string cookieStr) const {
+void CookieBox::parse(Cookie& cookie, const string& cookieStr) const {
   cookie.clear();
   Strings terms;
   Util::slice(terms, cookieStr, ';');
@@ -63,7 +63,7 @@ void CookieBox::parse(Cookie& cookie, string cookieStr) const {
   }
 }
 
-Cookies CookieBox::criteriaFind(string host, string dir, bool secure) const {
+Cookies CookieBox::criteriaFind(const string& host, const string& dir, bool secure) const {
   Cookies result;
   for(Cookies::const_iterator itr = cookies.begin(); itr != cookies.end(); itr++) {
     const Cookie& c = *itr;
diff --git a/src/CookieBox.h b/src/CookieBox.h
index 6892670a..f1d7770f 100644
--- a/src/CookieBox.h
+++ b/src/CookieBox.h
@@ -37,7 +37,7 @@ public:
   string domain;
   bool secure;
 public:
-  Cookie(string name, string value, string expires, string path, string domain, bool secure):name(name), value(value), expires(expires), path(path), domain(domain), secure(secure) {}
+  Cookie(const string& name, const string& value, const string& expires, const string& path, const string& domain, bool secure):name(name), value(value), expires(expires), path(path), domain(domain), secure(secure) {}
   Cookie():secure(false) {}
   ~Cookie() {}
   string toString() const {
@@ -54,15 +54,15 @@ typedef deque<Cookie> Cookies;
 class CookieBox {
 private:
   Cookies cookies;
-  void setField(Cookie& cookie, string name, string value) const;
+  void setField(Cookie& cookie, const string& name, const string& value) const;
 public:
   CookieBox();
   ~CookieBox();
   void clear();
   void add(const Cookie& cookie);
-  void add(string cookieStr);
-  void parse(Cookie& cookie, string cookieStr) const;
-  Cookies criteriaFind(string host, string dir, bool secure) const;
+  void add(const string& cookieStr);
+  void parse(Cookie& cookie, const string& cookieStr) const;
+  Cookies criteriaFind(const string& host, const string& dir, bool secure) const;
 };
 
 #endif // _D_COOKIE_BOX_H_
diff --git a/src/FtpConnection.cc b/src/FtpConnection.cc
index dac5a387..e265beb1 100644
--- a/src/FtpConnection.cc
+++ b/src/FtpConnection.cc
@@ -108,7 +108,7 @@ void FtpConnection::sendRetr() const {
   socket->writeData(request);
 }
 
-int FtpConnection::getStatus(string response) const {
+int FtpConnection::getStatus(const string& response) const {
   int status;
   // When the response is not like "%d %*s",
   // we return 0.
@@ -123,7 +123,7 @@ int FtpConnection::getStatus(string response) const {
   }
 }
 
-bool FtpConnection::isEndOfResponse(int status, string response) const {
+bool FtpConnection::isEndOfResponse(int status, const string& response) const {
   if(response.size() <= 4) {
     return false;
   }
diff --git a/src/FtpConnection.h b/src/FtpConnection.h
index 7b5ec17e..7e37506a 100644
--- a/src/FtpConnection.h
+++ b/src/FtpConnection.h
@@ -42,8 +42,8 @@ private:
 
   string strbuf;
 
-  int getStatus(string response) const;
-  bool isEndOfResponse(int status, string response) const;
+  int getStatus(const string& response) const;
+  bool isEndOfResponse(int status, const string& response) const;
   bool bulkReceiveResponse(pair<int, string>& response);
 public:
   FtpConnection(int cuid, const Socket* socket, const Request* req, const Option* op, const Logger* logger);
diff --git a/src/Peer.h b/src/Peer.h
index 41b323ac..ace51d38 100644
--- a/src/Peer.h
+++ b/src/Peer.h
@@ -45,9 +45,7 @@ public:
   int cuid;
 private:
   char peerId[PEER_ID_LENGTH];
-  //unsigned char* bitfield;
   BitfieldMan* bitfield;
-  //int bitfieldLength;
   long long int peerUpload;
   long long int peerDownload;
   int pieceLength;
@@ -58,7 +56,7 @@ public:
     amChocking(true), amInterested(false),
     peerChoking(true), peerInterested(false),
     tryCount(0), error(0), cuid(0),
-    bitfield(NULL),// bitfieldLength(0),
+    bitfield(NULL),
     peerUpload(0), peerDownload(0),
     pieceLength(pieceLength), totalLength(totalLength) {
     this->bitfield = new BitfieldMan(pieceLength, totalLength);
@@ -66,7 +64,7 @@ public:
 
   ~Peer() {
     if(bitfield != NULL) {
-      delete /*[]*/ bitfield;
+      delete bitfield;
     }
   }
 
@@ -77,22 +75,10 @@ public:
   
   void setBitfield(const unsigned char* bitfield, int bitfieldLength) {
     this->bitfield->setBitfield(bitfield, bitfieldLength);
-    /*
-    if(this->bitfield != NULL) {
-      delete [] this->bitfield;
-    }
-    this->bitfieldLength = bitfieldLength;
-    this->bitfield = new unsigned char[this->bitfieldLength];
-    memcpy(this->bitfield, bitfield, this->bitfieldLength);
-    */
   }
   const unsigned char* getBitfield() const { return bitfield->getBitfield(); }
   int getBitfieldLength() const { return bitfield->getBitfieldLength(); }
 
-  /*
-  void initBitfield(int pieces);
-  */
-
   /**
    * operation = 1: set index-th bit 1
    * operation = 0: set index-th bit 0
diff --git a/src/PeerMessageUtil.cc b/src/PeerMessageUtil.cc
index 0585866a..29b1768d 100644
--- a/src/PeerMessageUtil.cc
+++ b/src/PeerMessageUtil.cc
@@ -151,8 +151,13 @@ void PeerMessageUtil::checkPieceOffset(const PeerMessage* message, int pieceLeng
 }
 
 void PeerMessageUtil::checkLength(const PeerMessage* message) {
-  if(message->getLength() > 128*1024) {
-    throw new DlAbortEx("too large length %d > 128KB", message->getLength());
+  if(message->getLength() > MAX_BLOCK_LENGTH) {
+    throw new DlAbortEx("too large length %d > %dKB", message->getLength(),
+			MAX_BLOCK_LENGTH/1024);
+  }
+  if(!Util::isPowerOf(message->getLength(), 2)) {
+    throw new DlAbortEx("invalid length %d, which is not power of 2",
+			message->getLength());
   }
 }
 
diff --git a/src/PeerMessageUtil.h b/src/PeerMessageUtil.h
index 47e74049..ca8ae522 100644
--- a/src/PeerMessageUtil.h
+++ b/src/PeerMessageUtil.h
@@ -24,6 +24,8 @@
 
 #include "PeerConnection.h"
 
+#define MAX_BLOCK_LENGTH (128*1024)
+
 class PeerMessageUtil {
 private:
   PeerMessageUtil() {}
diff --git a/src/Piece.h b/src/Piece.h
index d8d7d95d..9d77576f 100644
--- a/src/Piece.h
+++ b/src/Piece.h
@@ -25,7 +25,7 @@
 #include "BitfieldMan.h"
 #include "common.h"
 
-#define BLOCK_LENGTH 16*1024
+#define BLOCK_LENGTH (16*1024)
 
 class Piece {
 private:
diff --git a/src/TorrentMan.h b/src/TorrentMan.h
index 866ffda7..a4f6cedd 100644
--- a/src/TorrentMan.h
+++ b/src/TorrentMan.h
@@ -35,18 +35,11 @@
 
 using namespace std;
 
-#define DEFAULT_BLOCK_LEN 16*1024;
-#define MAX_BLOCK_LEN 128*1024;
-
 #define INFO_HASH_LENGTH 20
-
-#define IS_NULL_PIECE(X) (X.index == 0 && X.length == 0)
-
 #define DEFAULT_ANNOUNCE_INTERVAL 300
 #define DEFAULT_ANNOUNCE_MIN_INTERVAL 300
 #define MAX_PEERS 55
 #define MAX_PEER_UPDATE 15
-
 #define MAX_PEER_LIST_SIZE 250
 #define END_GAME_PIECE_NUM 20
 #define MAX_PEER_ERROR 5
diff --git a/src/Util.cc b/src/Util.cc
index 5396d60c..ee7f5693 100644
--- a/src/Util.cc
+++ b/src/Util.cc
@@ -59,7 +59,7 @@ string Util::llitos(long long int value, bool comma)
   return str;
 }
 
-string Util::trim(string src) {
+string Util::trim(const string& src) {
   string::size_type sp = src.find_first_not_of(" ");
   string::size_type ep = src.find_last_not_of(" ");
   if(sp == string::npos || ep == string::npos) {
@@ -69,7 +69,7 @@ string Util::trim(string src) {
   }
 }
 
-void Util::split(pair<string, string>& hp, string src, char delim) {
+void Util::split(pair<string, string>& hp, const string& src, char delim) {
   hp.first = "";
   hp.second = "";
   string::size_type p = src.find(delim);
@@ -90,7 +90,7 @@ long long int Util::difftv(struct timeval tv1, struct timeval tv2) {
 	  tv1.tv_usec-tv2.tv_usec);
 }
 
-void Util::slice(Strings& result, string src, char delim) {
+void Util::slice(Strings& result, const string& src, char delim) {
   string::size_type p = 0;
   while(1) {
     string::size_type np = src.find(delim, p);
@@ -107,7 +107,7 @@ void Util::slice(Strings& result, string src, char delim) {
   } 
 }
 
-bool Util::startsWith(string target, string part) {
+bool Util::startsWith(const string& target, const string& part) {
   if(target.size() < part.size()) {
     return false;
   }
@@ -121,7 +121,7 @@ bool Util::startsWith(string target, string part) {
   }
 }
 
-bool Util::endsWith(string target, string part) {
+bool Util::endsWith(const string& target, const string& part) {
   if(target.size() < part.size()) {
     return false;
   }
@@ -135,7 +135,7 @@ bool Util::endsWith(string target, string part) {
   }
 }
 
-string Util::replace(string target, string oldstr, string newstr) {
+string Util::replace(const string& target, const string& oldstr, const string& newstr) {
   if(target == "" || oldstr == "" ) {
     return target;
   }
@@ -186,17 +186,17 @@ string Util::toHex(const unsigned char* src, int len) {
   return hex;
 }
 
-FILE* Util::openFile(string filename, string mode) {
+FILE* Util::openFile(const string& filename, const string& mode) {
   FILE* file = fopen(filename.c_str(), mode.c_str());
   return file;
 }
 
-void Util::fileCopy(string dest, string src) {
+void Util::fileCopy(const string& dest, const string& src) {
   File file(src);
   rangedFileCopy(dest, src, 0, file.size());
 }
 
-void Util::rangedFileCopy(string dest, string src, long long int srcOffset, long long int length) {
+void Util::rangedFileCopy(const string& dest, const string& src, long long int srcOffset, long long int length) {
   int bufSize = 4096;
   char buf[bufSize];
   int destFd = -1;
@@ -246,3 +246,15 @@ void Util::rangedFileCopy(string dest, string src, long long int srcOffset, long
   }
 }
 
+bool Util::isPowerOf(int num, int base) {
+  if(base <= 0) { return false; }
+  if(base == 1) { return true; }
+
+  while(num%base == 0) {
+    num /= base;
+    if(num == 1) {
+      return true;
+    }
+  }
+  return false;
+}
diff --git a/src/Util.h b/src/Util.h
index 6b96b6a1..8375c65b 100644
--- a/src/Util.h
+++ b/src/Util.h
@@ -34,7 +34,7 @@ using namespace std;
 
 class Util {
 public:
-  static void split(pair<string, string>& hp, string src, char delim);
+  static void split(pair<string, string>& hp, const string& src, char delim);
   static string llitos(long long int value, bool comma = false);
   static string itos(int value, bool comma = false);
   /**
@@ -47,26 +47,27 @@ public:
    * Take a string src which is a deliminated list and add its elements
    * into result. result is not cleared before conversion begins.
    */
-  static void slice(Strings& result, string src, char delim);
+  static void slice(Strings& result, const string& src, char delim);
   
-  static string trim(string src);
+  static string trim(const string& src);
 
-  static bool startsWith(string target, string part);
+  static bool startsWith(const string& target, const string& part);
 
-  static bool endsWith(string target, string part);
+  static bool endsWith(const string& target, const string& part);
 
-  static string replace(string target, string oldstr, string newstr);
+  static string replace(const string& target, const string& oldstr, const string& newstr);
 
   static string urlencode(const unsigned char* target, int len);
 
   static string toHex(const unsigned char* src, int len);
 
-  static FILE* openFile(string filename, string mode);
+  static FILE* openFile(const string& filename, const string& mode);
 
-  static void fileCopy(string destFile, string src);
+  static void fileCopy(const string& destFile, const string& src);
 
-  static void rangedFileCopy(string destFile, string src, long long int srcOffset, long long int length);
+  static void rangedFileCopy(const string& destFile, const string& src, long long int srcOffset, long long int length);
 
+  static bool isPowerOf(int num, int base);
 };
 
 #endif // _D_UTIL_H_