* generic/tclExecute.c: added comments to the alignment macros

	used in GrowEvaluationStack() and friends.

2 files changed, 23 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 0adcdde..6c30da3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-04-08  Miguel Sofer  <msofer@users.sf.net>
+
+	* generic/tclExecute.c: added comments to the alignment macros
+	used in GrowEvaluationStack() and friends.
+	
 2008-04-08  Daniel Steffen  <das@users.sourceforge.net>
 
 	* tools/genStubs.tcl:	revert erroneous 2008-04-02 change marking
diff --git a/generic/tclExecute.c b/generic/tclExecute.c
index 1677a78..c7e3e08 100644
--- a/generic/tclExecute.c
+++ b/generic/tclExecute.c
@@ -13,7 +13,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclExecute.c,v 1.369 2008/03/18 18:52:07 msofer Exp $
+ * RCS: @(#) $Id: tclExecute.c,v 1.370 2008/04/08 15:11:30 msofer Exp $
  */
 
 #include "tclInt.h"
@@ -851,23 +851,36 @@ TclFinalizeExecution(void)
 
 /*
  * Auxiliary code to insure that GrowEvaluationStack always returns correctly 
- * aligned memory. This assumes that TCL_ALLOCALIGN is a multiple of the
- * wordsize 'sizeof(Tcl_Obj *)'. 
+ * aligned memory.
+ *
+ * WALLOCALIGN represents the alignment reqs in words, just as TCL_ALLOCALIGN
+ * represents the reqs in bytes. This assumes that TCL_ALLOCALIGN is a
+ * multiple of the wordsize 'sizeof(Tcl_Obj *)'. 
  */
 
 #define WALLOCALIGN \
     (TCL_ALLOCALIGN/sizeof(Tcl_Obj *))
 
+/*
+ * OFFSET computes how many words have to be skipped until the next aligned
+ * word. Note that we are only interested in the low order bits of ptr, so
+ * that any possible information loss in PTR2INT is of no consequence.
+ */
+
 static inline int
 OFFSET(
     void *ptr)
 {
     int mask = TCL_ALLOCALIGN-1;
     int base = PTR2INT(ptr) & mask;
-    return (TCL_ALLOCALIGN - base)/sizeof(Tcl_Obj**);
+    return (TCL_ALLOCALIGN - base)/sizeof(Tcl_Obj *);
 }
 
-#define MEMSTART(markerPtr) \
+/*
+ * Given a marker, compute where the following aligned memory starts. 
+ */
+
+#define MEMSTART(markerPtr)			\
     ((markerPtr) + OFFSET(markerPtr))