From 28f3aa0a8e86ea3ecd2e2699fa20fd08c6c22763 Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Tue, 17 Feb 2009 06:52:05 +0000
Subject:         * generic/tclStringObj.c:       Revise buffer growth
 implementation         in ExtendStringRepWithUnicode.  Use cheap checks to
 determine that         no reallocation is necessary without cost of computing
 the precise         number of bytes needed.  Also make use of the string
 growth algortihm         in the case of repeated appends.

---
 ChangeLog              | 22 ++++++++++++++--------
 generic/tclStringObj.c | 45 ++++++++++++++++++++++++++++++++-------------
 2 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b896f98..a51a52c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,15 +1,21 @@
-2009-02-16  Jan Nijtmans  <nijtmans@users.sf.net>
+2009-02-17  Don Porter  <dgp@users.sourceforge.net>
 
-    * generic/tclZlib.c      hack needed for official zlib1.dll build. 
-	* win/configure.in       fix [Feature Request 2605263] use official
-	* win/Makefile.in        zlib build.
-	* win/configure          (regenerated)
-	* compat/zlib/zdll.lib   new files
-	* compat/zlib/zlib1.dll
+	* generic/tclStringObj.c:	Revise buffer growth implementation
+	in ExtendStringRepWithUnicode.  Use cheap checks to determine that
+	no reallocation is necessary without cost of computing the precise
+	number of bytes needed.  Also make use of the string growth algortihm
+	in the case of repeated appends.
 
 2009-02-16  Jan Nijtmans  <nijtmans@users.sf.net>
 
-	* win/Makefile.in  fix [Bug 2605232] tdbc doesn't build when
+	* generic/tclZlib.c:	hack needed for official zlib1.dll build. 
+	* win/configure.in:	fix [Feature Request 2605263] use official
+	* win/Makefile.in:	zlib build.
+	* win/configure:	(regenerated)
+	* compat/zlib/zdll.lib:	new files
+	* compat/zlib/zlib1.dll:
+
+	* win/Makefile.in:  fix [Bug 2605232] tdbc doesn't build when
 	Tcl is compiled with --disable-shared.
 
 2009-02-15  Don Porter  <dgp@users.sourceforge.net>
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index ecea7be..52e6019 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -33,7 +33,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclStringObj.c,v 1.109 2009/02/16 04:06:07 dgp Exp $ */
+ * RCS: @(#) $Id: tclStringObj.c,v 1.110 2009/02/17 06:52:05 dgp Exp $ */
 
 #include "tclInt.h"
 #include "tommath.h"
@@ -2897,7 +2897,7 @@ ExtendStringRepWithUnicode(
     const Tcl_UniChar *unicode,
     int numChars)
 {
-    int i, size = 0;	
+    int i, origLength, size = 0;	
     char *dst, buf[TCL_UTF_MAX];
 
     /* Pre-condition: this is the "string" Tcl_ObjType */
@@ -2918,12 +2918,13 @@ ExtendStringRepWithUnicode(
     } else {
 	objPtr->length = 0;
     }
+    origLength = objPtr->length;
     
-    /*
-     * TODO: Consider fast overallocation of numChars*TCL_UTF_MAX bytes.
-     * Then we could make one pass instead of two.  Trade away memory
-     * efficiency for speed.
-     */
+    /* Quick cheap check in case we have more than enough room. */
+    if (numChars <= (INT_MAX - size)/TCL_UTF_MAX 
+	    && stringPtr->allocated >= size + numChars * TCL_UTF_MAX) {
+	goto copyBytes;
+    }
 
     for (i = 0; i < numChars && size >= 0; i++) {
 	size += Tcl_UniCharToUtf((int) unicode[i], buf);
@@ -2934,16 +2935,34 @@ ExtendStringRepWithUnicode(
 
     /* Grow space if needed */
     if (size > stringPtr->allocated) {
-	/* TODO: Growth algorithm for appends ? */
-	objPtr->bytes = ckrealloc(objPtr->bytes, (unsigned) size+1);
-	stringPtr->allocated = size;
+	if (stringPtr->allocated == 0) {
+	    /* First allocation - just big enough */
+	    objPtr->bytes = ckrealloc(objPtr->bytes, (unsigned) size+1);
+	    stringPtr->allocated = size;
+	} else {
+	    /* Subsequent appends - apply the growth algorithm. */
+	    if (Tcl_AttemptSetObjLength(objPtr, 2 * size) == 0) {
+		/*
+		 * Take care computing the amount of modest growth to avoid
+		 * overflow into invalid argument values for Tcl_SetObjLength.
+		 */
+		unsigned int limit = INT_MAX - size;
+		unsigned int extra = size - objPtr->length
+			+ TCL_GROWTH_MIN_ALLOC;
+		int growth = (int) ((extra > limit) ? limit : extra);
+
+		Tcl_SetObjLength(objPtr, size + growth);
+	    }
+	}
     }
-    dst = objPtr->bytes + objPtr->length;
+
+    copyBytes:
+    dst = objPtr->bytes + origLength;
     for (i = 0; i < numChars; i++) {
 	dst += Tcl_UniCharToUtf((int) unicode[i], dst);
     }
-    objPtr->length = size;
-    objPtr->bytes[size] = '\0';
+    *dst = '\0';
+    objPtr->length = dst - objPtr->bytes;
     return numChars;
 }
 
-- 
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