Improve efficiency of Tcl_AppendObjToObj's bytearray handling.

2 files changed, 37 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 9136545..65a4067 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2009-02-05  Donal K. Fellows  <dkf@users.sf.net>
+
+	* generic/tclStringObj.c (Tcl_AppendObjToObj): Special-case the
+	appending of one bytearray to another, which can be extremely rapid.
+	Part of scheme to address [Bug 1665628] by making the basic string
+	operations more efficient on byte arrays.
+
 2009-02-04  Don Porter  <dgp@users.sourceforge.net>
 
 	* generic/tclStringObj.c: Added overflow protections to the
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index fc19ce6..b7961b8 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 1.84 2009/02/04 21:45:19 dgp Exp $ */
+ * RCS: @(#) $Id: tclStringObj.c,v 1.85 2009/02/05 01:21:59 dkf Exp $ */
 
 #include "tclInt.h"
 #include "tommath.h"
@@ -1216,6 +1216,35 @@ Tcl_AppendObjToObj(
     int length, numChars, allOneByteChars;
     char *bytes;
 
+    /*
+     * Handle append of one bytearray object to another as a special case.
+     * Note that we only do this when the object being written doesn't have a
+     * string rep; if it did, then appending the byte arrays together could
+     * well lose information; this is a special-case optimization only.
+     */
+
+    if (objPtr->typePtr == &tclByteArrayType && objPtr->bytes == NULL
+	    && appendObjPtr->typePtr == &tclByteArrayType) {
+	unsigned char *bytesDst, *bytesSrc;
+	int lengthSrc, lengthTotal;
+
+	/*
+	 * Note that we do not assume that objPtr and appendObjPtr must be
+	 * distinct!
+	 */
+
+	(void) Tcl_GetByteArrayFromObj(objPtr, &length);
+	(void) Tcl_GetByteArrayFromObj(appendObjPtr, &lengthSrc);
+	lengthTotal = length + lengthSrc;
+	if (((length > lengthSrc) ? length : lengthSrc) > lengthTotal) {
+	    Tcl_Panic("overflow when calculating byte array size");
+	}
+	bytesDst = Tcl_SetByteArrayLength(objPtr, lengthTotal);
+	bytesSrc = Tcl_GetByteArrayFromObj(appendObjPtr, NULL);
+	memcpy(bytesDst + length, bytesSrc, lengthSrc);
+	return;
+    }
+
     SetStringFromAny(NULL, objPtr);
 
     /*