Index: TODO
===================================================================
diff -u -rcd557a4c6f4d0b3c408a48b6059b5a9a9c20296f -r760d5e6aa44c07331fea3c109385c309d906779c
--- TODO	(.../TODO)	(revision cd557a4c6f4d0b3c408a48b6059b5a9a9c20296f)
+++ TODO	(.../TODO)	(revision 760d5e6aa44c07331fea3c109385c309d906779c)
@@ -5767,6 +5767,8 @@
   triggering creation attempts in ttrace via 
       ::nsf::object::alloc SOMECLASS SOMEOBJ
 
+- added Tcl_HashKeyType cmdPtrHashKeyType for command pointers
+
 ========================================================================
 TODO:
 
Index: generic/nsfCmdDefinitions.c
===================================================================
diff -u -r16a02881bff0a0d626d0045dfd96660338d0c314 -r760d5e6aa44c07331fea3c109385c309d906779c
--- generic/nsfCmdDefinitions.c	(.../nsfCmdDefinitions.c)	(revision 16a02881bff0a0d626d0045dfd96660338d0c314)
+++ generic/nsfCmdDefinitions.c	(.../nsfCmdDefinitions.c)	(revision 760d5e6aa44c07331fea3c109385c309d906779c)
@@ -4,7 +4,7 @@
  *      Provide API for registering method definitions
  *      and obtaining this data for introspection
  *
- * Copyright (C) 2014 Gustaf Neumann
+ * Copyright (C) 2014-2016 Gustaf Neumann
  *
  * Vienna University of Economics and Business
  * Institute of Information Systems and New Media
@@ -43,8 +43,153 @@
 
 static int Register(Tcl_Interp *interp, Nsf_methodDefinition *methodDefinition);
 
+
 /*
+ * Defintions for HashType cmdPtr.
+ *
+ * Background: since it is not guaranteed that sizeof(function pointer) ==
+ * sizeof(data pointer) (or sizeof(function pointer) <= sizeof(data pointer)),
+ * passing function pointers via data pointers - which is the default tcl hash
+ * types do - is dangerous. So we define our own type that allows to hash on
+ * function pointers safely.
+ *
+ */
+static unsigned int CmdPtrKey(Tcl_HashTable *tablePtr, VOID *keyPtr);
+static int CompareCmdPtrKeys(VOID *keyPtr, Tcl_HashEntry *hPtr);
+static Tcl_HashEntry *AllocCmdPtrEntry(Tcl_HashTable *tablePtr, VOID *keyPtr);
+
+typedef struct cmdPtrEntry_t {
+  Tcl_ObjCmdProc *proc;
+} cmdPtrEntry_t;
+
+static Tcl_HashKeyType cmdPtrHashKeyType = {
+  1,                 /* version*/
+  0,                 /* flags */
+  CmdPtrKey,         /* hashKeyProc*/
+  CompareCmdPtrKeys, /* compareKeysProc */
+  AllocCmdPtrEntry,  /* allocEntryProc */
+  NULL,              /* freeEntryProc */
+};
+
+/*
  *----------------------------------------------------------------------
+ *
+ * CmdPtrKey --
+ *
+ *	Compute a unsigned int hash value from a function pointer.
+ *
+ * Results:
+ *	Hash value.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static unsigned int
+CmdPtrKey(
+          Tcl_HashTable *tablePtr, /* Hash table. */
+          VOID *keyPtr)		   /* Key from which to compute hash value. */
+{
+  cmdPtrEntry_t  *cmdEntryPtr = (cmdPtrEntry_t *)keyPtr;
+  Tcl_ObjCmdProc *value  = cmdEntryPtr->proc;
+
+  //fprintf(stderr, "=== hash from %p = %u // 0x%x\n", (void *)value, PTR2UINT(value), PTR2UINT(value));
+  /*
+   * This is a very simple approach for obtaining a hash value. Maybe one
+   * needs a more sophisticated approach with wierd endians machines.
+   */
+  return PTR2UINT(value);
+
+  /*
+    as a reference: tcl's string hash functions
+
+    register unsigned int result;
+    register int c;
+    result = 0;
+
+    for (c=*string++ ; c ; c=*string++) {
+    result += (result<<3) + c;
+    }
+    return result;
+  */
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * CompareCmdPtrKeys --
+ *
+ *	Compares two cmd ptr keys.
+ *
+ * Results:
+ *	The return value is 0 if they are different and 1 if they are the
+ *	same.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+CompareCmdPtrKeys(
+                  VOID *keyPtr,		/* New key to compare. */
+                  Tcl_HashEntry *hPtr)	/* Existing key to compare. */
+{
+  cmdPtrEntry_t  *cmdEntryPtr = (cmdPtrEntry_t *)keyPtr;
+  Tcl_ObjCmdProc *existingValue;
+
+  memcpy(&existingValue, &hPtr->key.oneWordValue, sizeof(Tcl_ObjCmdProc *));
+
+  //fprintf(stderr, "=== compare new %p existing %p\n", (void *)cmdPtr->proc, (void *)existingValue);
+
+  return cmdEntryPtr->proc == existingValue;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * AllocCmdPtrEntry --
+ *
+ *	Allocate space for a Tcl_HashEntry containing the cmd ptr
+ *
+ * Results:
+ *	The return value is a pointer to the created entry.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+static Tcl_HashEntry *
+AllocCmdPtrEntry(
+                 Tcl_HashTable *tablePtr,   /* Hash table. */
+                 VOID *keyPtr)		    /* Key to store in the hash table entry. */
+{
+  cmdPtrEntry_t   *cmdEntryPtr = (cmdPtrEntry_t *)keyPtr;
+  Tcl_HashEntry   *hPtr;
+  unsigned int     size;
+  Tcl_ObjCmdProc  *value = cmdEntryPtr->proc;
+
+  size = sizeof(Tcl_HashEntry) + (sizeof(Tcl_ObjCmdProc *)) - sizeof(hPtr->key);
+  if (size < sizeof(Tcl_HashEntry)) {
+    size = sizeof(Tcl_HashEntry);
+  }
+  //fprintf(stderr, "=== alloc entry %p\n", (void *)value);
+  hPtr = (Tcl_HashEntry *) ckalloc(size);
+
+  //fprintf(stderr, "=== trying to copy %ld bytes from %p to %p\n", sizeof(Tcl_ObjCmdProc *), (void *)value, &hPtr->key.oneWordValue);
+  memcpy(&hPtr->key.oneWordValue, &value, sizeof(Tcl_ObjCmdProc *));
+
+  hPtr->clientData = 0;
+
+  return hPtr;
+}
+
+/*
+ *----------------------------------------------------------------------
  * Nsf_CmdDefinitionInit --
  *
  *    Initialize cmd definition structures
@@ -65,13 +210,15 @@
   NsfMutexLock(&cmdDefinitonMutex);
 
   if (cmdDefinitonRefCount == 0) {
-    Tcl_InitHashTable(cmdDefinitonHashTablePtr, TCL_ONE_WORD_KEYS);
+    // Tcl_InitHashTable(cmdDefinitonHashTablePtr, TCL_ONE_WORD_KEYS);
+    Tcl_InitCustomHashTable(cmdDefinitonHashTablePtr, TCL_CUSTOM_PTR_KEYS, &cmdPtrHashKeyType);
   }
   cmdDefinitonRefCount++;
 
   NsfMutexUnlock(&cmdDefinitonMutex);
 }
 
+
 /*
  *----------------------------------------------------------------------
  * Nsf_CmdDefinitionRegister --
@@ -117,11 +264,15 @@
 Nsf_methodDefinition *
 Nsf_CmdDefinitionGet(Tcl_ObjCmdProc *proc) {
   Tcl_HashEntry *hPtr;
+  cmdPtrEntry_t cmdEntry;
 
   nonnull_assert(proc != NULL);
 
+  //fprintf(stderr, "=== Lookup proc %p\n", proc);
+  cmdEntry.proc = proc;
+
   NsfMutexLock(&cmdDefinitonMutex);
-  hPtr = Tcl_FindHashEntry(cmdDefinitonHashTablePtr, (char *)proc);
+  hPtr = Tcl_FindHashEntry(cmdDefinitonHashTablePtr, (const char *)&cmdEntry);
   NsfMutexUnlock(&cmdDefinitonMutex);
 
   if (hPtr != NULL) {
@@ -151,12 +302,15 @@
 Register(Tcl_Interp *interp, Nsf_methodDefinition *methodDefinition) {
   Tcl_HashEntry *hPtr;
   int isNew;
+  cmdPtrEntry_t cmdEntry;
 
   nonnull_assert(interp != NULL);
   nonnull_assert(methodDefinition != NULL);
 
+  //fprintf(stderr, "=== Register proc %p with name %s\n", methodDefinition->proc, methodDefinition->methodName);
+  cmdEntry.proc = methodDefinition->proc;
   NsfMutexLock(&cmdDefinitonMutex);
-  hPtr = Tcl_CreateHashEntry(cmdDefinitonHashTablePtr, (char *)methodDefinition->proc, &isNew);
+  hPtr = Tcl_CreateHashEntry(cmdDefinitonHashTablePtr, (const char *)&cmdEntry, &isNew);
   NsfMutexUnlock(&cmdDefinitonMutex);
 
   if (isNew != 0) {