diff --git a/ase/include/ase/cmn/sll.h b/ase/include/ase/cmn/sll.h
index c3532e38..b01f924c 100644
--- a/ase/include/ase/cmn/sll.h
+++ b/ase/include/ase/cmn/sll.h
@@ -22,10 +22,41 @@ typedef struct ase_sll_node_t ase_sll_node_t;
 typedef enum ase_sll_walk_t ase_sll_walk_t;
 
 /* data copier */
-typedef void* (*ase_sll_copier_t) (ase_sll_t* sll, void* dptr, ase_size_t dlen);
+typedef void* (*ase_sll_copier_t) (
+	ase_sll_t* sll,
+	void* dptr,
+	ase_size_t dlen
+);
 
 /* data freeer */
-typedef void (*ase_sll_freeer_t) (ase_sll_t* sll, void* dptr, ase_size_t dlen);
+typedef void (*ase_sll_freeer_t) (
+	ase_sll_t* sll,
+	void* dptr,
+	ase_size_t dlen
+);
+
+/****t* ase.cmn.sll/ase_sll_comper_t
+ * NAME
+ *  ase_sll_comper_t - define a data comparator
+ *
+ * DESCRIPTION
+ *  The ase_sll_comper_t type defines a key comparator that is called when
+ *  the list needs to compare data. A singly linked list is created with a
+ *  default comparator that performs bitwise comparison.
+ *
+ *  The comparator should return 0 if the data are the same and a non-zero
+ *  integer otherwise.
+ *
+ * SYNOPSIS
+ */
+typedef int (*ase_sll_comper_t) (
+	ase_sll_t* sll    /* a singly linked list */, 
+	const void* dptr1 /* a data pointer */,
+	ase_size_t dlen1  /* a data length */,
+	const void* dptr2 /* a data pointer */,
+	ase_size_t dlen2  /* a data length */
+);
+/******/
 
 /* node visitor */
 typedef ase_sll_walk_t (*ase_sll_walker_t) (
@@ -46,6 +77,7 @@ struct ase_sll_t
 
 	ase_sll_copier_t copier;
 	ase_sll_freeer_t freeer;
+	ase_sll_comper_t comper;
 	ase_byte_t scale;
 
 	ase_size_t size;
@@ -241,6 +273,15 @@ void ase_sll_setfreeer (
 );
 /******/
 
+ase_sll_comper_t ase_sll_getcomper (
+	ase_sll_t* sll
+);
+
+void ase_sll_setcomper (
+	ase_sll_t* sll          /* a singly linked list */,
+	ase_sll_comper_t comper /* a comparator */
+);
+
 /*
  * NAME: Gets the head(first) node 
  * RETURN: the tail node of a singly linked list
@@ -257,6 +298,22 @@ ase_sll_node_t* ase_sll_gettail (
 	ase_sll_t* sll /* a singly linked list */
 );
 
+/****f* ase.cmn.sll/ase_sll_search
+ * NAME
+ *  ase_sll_search - find a node
+ *
+ * DESCRIPTION
+ *  The ase_sll_search() function traverses the list to find a node containing
+ *  the same value as the the data pointer and length. 
+ *
+ * SYNOPSIS
+ */
+ase_sll_node_t* ase_sll_search (
+	ase_sll_t* sll    /* a singly linked list */,
+	const void* dptr  /* a data pointer */,
+	ase_size_t dlen   /* a data length */
+);
+
 /****f* ase.cmn.sll/ase_sll_insert
  * NAME
  *  ase_sll_insert - insert data before a positional node given 
diff --git a/ase/lib/cmn/sll.c b/ase/lib/cmn/sll.c
index 2b4ec598..71fe9692 100644
--- a/ase/lib/cmn/sll.c
+++ b/ase/lib/cmn/sll.c
@@ -11,6 +11,7 @@
 #define node_t   ase_sll_node_t
 #define copier_t ase_sll_copier_t
 #define freeer_t ase_sll_freeer_t
+#define comper_t ase_sll_comper_t
 #define walker_t ase_sll_walker_t
 
 #define HEAD(s) ASE_SLL_HEAD(s)
@@ -26,6 +27,15 @@
 #define size_t   ase_size_t
 #define mmgr_t   ase_mmgr_t
 
+static int comp_data (sll_t* sll, 
+	const void* dptr1, size_t dlen1, 
+	const void* dptr2, size_t dlen2)
+{
+	if (dlen1 == dlen2) return ASE_MEMCMP (dptr1, dptr2, TOB(sll,dlen1));
+	/* it just returns 1 to indicate that they are different. */
+	return 1;
+}
+
 sll_t* ase_sll_open (mmgr_t* mmgr, size_t ext)
 {
 	sll_t* sll;
@@ -59,6 +69,8 @@ sll_t* ase_sll_init (sll_t* sll, mmgr_t* mmgr)
 	sll->mmgr = mmgr;
 	sll->size = 0;
 	sll->scale = 1;
+
+	sll->comper = comp_data;
 	return sll;
 }
 
@@ -133,6 +145,16 @@ void ase_sll_setfreeer (sll_t* sll, freeer_t freeer)
 	sll->freeer = freeer;
 }
 
+comper_t ase_sll_getcomper (sll_t* sll)
+{
+	return sll->comper;
+}
+
+void ase_sll_setcomper (sll_t* sll, comper_t comper)
+{
+	sll->comper = comper;
+}
+
 static node_t* alloc_node (sll_t* sll, void* dptr, size_t dlen)
 {
 	node_t* n;