diff --git a/src/ecma119.c b/src/ecma119.c
index 7bd5579..c1f672b 100644
--- a/src/ecma119.c
+++ b/src/ecma119.c
@@ -136,10 +136,12 @@ int ecma119_writer_compute_data_blocks(IsoImageWriter *writer)
     target = writer->target;
     
     /* compute position of directories */
+    iso_msg_debug(target->image, "Computing position of dir structure");
     target->ndirs = 0;
     calc_dir_pos(target, target->root);
     
     /* compute length of pathlist */
+    iso_msg_debug(target->image, "Computing length of pathlist");
     path_table_size = calc_path_table_size(target->root);
     
     /* compute location for path tables */
@@ -529,6 +531,7 @@ int ecma119_writer_create(Ecma119Image *target)
     /* add this writer to image */
     target->writers[target->nwriters++] = writer;
     
+    iso_msg_debug(target->image, "Creating low level ECMA-119 tree...");
     ret = ecma119_tree_create(target);
     if (ret < 0) {
         return ret;
diff --git a/src/ecma119_tree.c b/src/ecma119_tree.c
index ea479e5..bab27ee 100644
--- a/src/ecma119_tree.c
+++ b/src/ecma119_tree.c
@@ -25,6 +25,7 @@ int get_iso_name(Ecma119Image *img, IsoNode *iso, char **name)
 {
     int ret;
     char *ascii_name;
+    char *isoname = NULL;
 
     if (iso->name == NULL) {
         /* it is not necessarily an error, it can be the root */
@@ -41,19 +42,28 @@ int get_iso_name(Ecma119Image *img, IsoNode *iso, char **name)
     // TODO add support for relaxed constraints
     if (iso->type == LIBISO_DIR) {
         if (img->iso_level == 1) {
-            iso_dirid(ascii_name, 8);
+            isoname = iso_1_dirid(ascii_name);
         } else {
-            iso_dirid(ascii_name, 31);
+            isoname = iso_2_dirid(ascii_name);
         }
     } else {
         if (img->iso_level == 1) {
-            iso_1_fileid(ascii_name);
+            isoname = iso_1_fileid(ascii_name);
         } else {
-            iso_2_fileid(ascii_name);
+            isoname = iso_2_fileid(ascii_name);
         }
     }
-    *name = ascii_name;
-    return ISO_SUCCESS;
+    free(ascii_name);
+    if (isoname != NULL) {
+        *name = isoname;
+        return ISO_SUCCESS;
+    } else {
+        /* 
+         * only possible if mem error, as check for empty names is done
+         * in public tree
+         */
+        return ISO_MEM_ERROR;   
+    }
 }
 
 static
diff --git a/src/util.c b/src/util.c
index 1d8b96c..e850388 100644
--- a/src/util.c
+++ b/src/util.c
@@ -202,62 +202,87 @@ static int valid_a_char(char c)
            || (c >= 'A' && c <= 'Z') || (c == '_');
 }
 
-void iso_dirid(char *src, int maxlen)
+static 
+char *iso_dirid(const char *src, int size)
 {
     size_t len, i;
-
+    char name[32];
+    
     len = strlen(src);
-    if (len > maxlen) {
-        src[maxlen] = '\0';
-        len = maxlen;
+    if (len > size) {
+        len = size;
     }
     for (i = 0; i < len; i++) {
         char c = toupper(src[i]);
-        src[i] = valid_d_char(c) ? c : '_';
+        name[i] = valid_d_char(c) ? c : '_';
     }
+    
+    name[len] = '\0';
+    return strdup(name);
 }
 
-void iso_1_fileid(char *src)
+char *iso_1_dirid(const char *src)
 {
-    char *dot; /* Position of the last dot in the filename, will be used to 
-                  calculate lname and lext. */
-    int lname, lext, pos, i;
+    return iso_dirid(src, 8);
+}
 
+char *iso_2_dirid(const char *src)
+{
+    return iso_dirid(src, 31);
+}
+
+char *iso_1_fileid(const char *src)
+{
+    char *dot; /* Position of the last dot in the filename, will be used 
+                  to calculate lname and lext. */
+    int lname, lext, pos, i;
+    char dest[13]; /*  13 = 8 (name) + 1 (.) + 3 (ext) + 1 (\0) */
+
+    if (src == NULL) {
+        return NULL;
+    }
     dot = strrchr(src, '.');
 
     lext = dot ? strlen(dot + 1) : 0;
     lname = strlen(src) - lext - (dot ? 1 : 0);
 
-    /* If we can't build a filename, return. */
+    /* If we can't build a filename, return NULL. */
     if (lname == 0 && lext == 0) {
-        return;
+        return NULL;
     }
 
     pos = 0;
+    
     /* Convert up to 8 characters of the filename. */
     for (i = 0; i < lname && i < 8; i++) {
         char c = toupper(src[i]);
-        src[pos++] = valid_d_char(c) ? c : '_';
+
+        dest[pos++] = valid_d_char(c) ? c : '_';
     }
     
     /* This dot is mandatory, even if there is no extension. */
-    src[pos++] = '.';
+    dest[pos++] = '.';
     
     /* Convert up to 3 characters of the extension, if any. */
     for (i = 0; i < lext && i < 3; i++) {
         char c = toupper(src[lname + 1 + i]);
-        src[pos++] = valid_d_char(c) ? c : '_';
+
+        dest[pos++] = valid_d_char(c) ? c : '_';
     }
-    src[pos] = '\0';
+    
+    dest[pos] = '\0';
+    return strdup(dest);
 }
 
-void iso_2_fileid(char *src)
+char *iso_2_fileid(const char *src)
 {
     char *dot;
     int lname, lext, lnname, lnext, pos, i;
+    char dest[32]; /* 32 = 30 (name + ext) + 1 (.) + 1 (\0) */
 
-    if (!src)
-        return;
+    if (src == NULL) {
+        return NULL;
+    }
 
     dot = strrchr(src, '.');
 
@@ -280,23 +305,124 @@ void iso_2_fileid(char *src)
     }
 
     if (lnname == 0 && lnext == 0) {
-        return;
+        return NULL;
     }
 
     pos = 0;
+    
     /* Convert up to lnname characters of the filename. */
     for (i = 0; i < lnname; i++) {
         char c = toupper(src[i]);
-        src[pos++] = valid_d_char(c) ? c : '_';
+
+        dest[pos++] = valid_d_char(c) ? c : '_';
     }
-    src[pos++] = '.';
+    dest[pos++] = '.';
+    
     /* Convert up to lnext characters of the extension, if any. */
     for (i = 0; i < lnext; i++) {
         char c = toupper(src[lname + 1 + i]);
-        src[pos++] = valid_d_char(c) ? c : '_';
+
+        dest[pos++] = valid_d_char(c) ? c : '_';
     }
-    src[pos] = '\0';
+    dest[pos] = '\0';
+    return strdup(dest);
 }
+
+//void iso_dirid(char *src, int maxlen)
+//{
+//    size_t len, i;
+//
+//    len = strlen(src);
+//    if (len > maxlen) {
+//        src[maxlen] = '\0';
+//        len = maxlen;
+//    }
+//    for (i = 0; i < len; i++) {
+//        char c = toupper(src[i]);
+//        src[i] = valid_d_char(c) ? c : '_';
+//    }
+//}
+
+//void iso_1_fileid(char *src)
+//{
+//    char *dot; /* Position of the last dot in the filename, will be used to 
+//                  calculate lname and lext. */
+//    int lname, lext, pos, i;
+//
+//    dot = strrchr(src, '.');
+//
+//    lext = dot ? strlen(dot + 1) : 0;
+//    lname = strlen(src) - lext - (dot ? 1 : 0);
+//
+//    /* If we can't build a filename, return. */
+//    if (lname == 0 && lext == 0) {
+//        return;
+//    }
+//
+//    pos = 0;
+//    /* Convert up to 8 characters of the filename. */
+//    for (i = 0; i < lname && i < 8; i++) {
+//        char c = toupper(src[i]);
+//        src[pos++] = valid_d_char(c) ? c : '_';
+//    }
+//    
+//    /* This dot is mandatory, even if there is no extension. */
+//    src[pos++] = '.';
+//    
+//    /* Convert up to 3 characters of the extension, if any. */
+//    for (i = 0; i < lext && i < 3; i++) {
+//        char c = toupper(src[lname + 1 + i]);
+//        src[pos++] = valid_d_char(c) ? c : '_';
+//    }
+//    src[pos] = '\0';
+//}
+//
+//void iso_2_fileid(char *src)
+//{
+//    char *dot;
+//    int lname, lext, lnname, lnext, pos, i;
+//
+//    if (!src)
+//        return;
+//
+//    dot = strrchr(src, '.');
+//
+//    /* 
+//     * Since the maximum length can be divided freely over the name and
+//     * extension, we need to calculate their new lengths (lnname and
+//     * lnext). If the original filename is too long, we start by trimming
+//     * the extension, but keep a minimum extension length of 3. 
+//     */
+//    if (dot == NULL || *(dot + 1) == '\0') {
+//        lname = strlen(src);
+//        lnname = (lname > 30) ? 30 : lname;
+//        lext = lnext = 0;
+//    } else {
+//        lext = strlen(dot + 1);
+//        lname = strlen(src) - lext - 1;
+//        lnext = (strlen(src) > 31 && lext > 3)
+//            ? (lname < 27 ? 30 - lname : 3) : lext;
+//        lnname = (strlen(src) > 31) ? 30 - lnext : lname;
+//    }
+//
+//    if (lnname == 0 && lnext == 0) {
+//        return;
+//    }
+//
+//    pos = 0;
+//    /* Convert up to lnname characters of the filename. */
+//    for (i = 0; i < lnname; i++) {
+//        char c = toupper(src[i]);
+//        src[pos++] = valid_d_char(c) ? c : '_';
+//    }
+//    src[pos++] = '.';
+//    /* Convert up to lnext characters of the extension, if any. */
+//    for (i = 0; i < lnext; i++) {
+//        char c = toupper(src[lname + 1 + i]);
+//        src[pos++] = valid_d_char(c) ? c : '_';
+//    }
+//    src[pos] = '\0';
+//}
     
 int str2d_char(const char *icharset, const char *input, char **output)
 {
diff --git a/src/util.h b/src/util.h
index 700ce9a..a766f9b 100644
--- a/src/util.h
+++ b/src/util.h
@@ -47,35 +47,39 @@ int int_pow(int base, int power);
 int str2ascii(const char *icharset, const char *input, char **output);
 
 /**
- * Ensure a given string is a valid ISO directory identifier, modifying
- * it if needed.
+ * Create a level 1 directory identifier.
  * 
  * @param src
- *      The identifier, in ASCII encoding. It may be modified by the function.
- * @param maxlen
- *      Maximum length supported by current iso level.
+ *      The identifier, in ASCII encoding.
  */
-void iso_dirid(char *src, int maxlen);
+char *iso_1_dirid(const char *src);
 
 /**
- * Ensure a given string is a valid ISO level 1 file identifier, in 8.3 
- * format, modifying it if needed.
+ * Create a level 2 directory identifier.
+ * 
+ * @param src
+ *      The identifier, in ASCII encoding.
+ */
+char *iso_2_dirid(const char *src);
+
+/**
+ * Create a level 1 file identifier that consists of a name, in 8.3 
+ * format.
  * Note that version number is not added to the file name
  * 
  * @param src
- *      The identifier, in ASCII encoding. It may be modified by the function.
+ *      The identifier, in ASCII encoding.
  */
-void iso_1_fileid(char *src);
+char *iso_1_fileid(const char *src);
 
 /**
- * Ensure a given string is a valid ISO level 2 file identifier, modifying it
- * if needed.
+ * Create a level 2 file identifier.
  * Note that version number is not added to the file name
  * 
  * @param src
- *      The identifier, in ASCII encoding. It may be modified by the function.
+ *      The identifier, in ASCII encoding.
  */
-void iso_2_fileid(char *src);
+char *iso_2_fileid(const char *src);
 
 /**
  * Convert a given input string to d-chars.
diff --git a/test/test_util.c b/test/test_util.c
index 1e68c10..3d10f0d 100644
--- a/test/test_util.c
+++ b/test/test_util.c
@@ -29,6 +29,105 @@ static void test_round_up()
 	CU_ASSERT_EQUAL( round_up(14, 7), 14 );
 }
 
+static void test_iso_bb()
+{
+    uint8_t buf[8];
+    uint32_t num;
+    
+    num = 0x01020304;
+    iso_bb(buf, num, 4);
+    CU_ASSERT_EQUAL( buf[0], 0x04 );
+    CU_ASSERT_EQUAL( buf[1], 0x03 );
+    CU_ASSERT_EQUAL( buf[2], 0x02 );
+    CU_ASSERT_EQUAL( buf[3], 0x01 );
+    CU_ASSERT_EQUAL( buf[4], 0x01 );
+    CU_ASSERT_EQUAL( buf[5], 0x02 );
+    CU_ASSERT_EQUAL( buf[6], 0x03 );
+    CU_ASSERT_EQUAL( buf[7], 0x04 );
+            
+    iso_bb(buf, num, 2);
+    CU_ASSERT_EQUAL( buf[0], 0x04 );
+    CU_ASSERT_EQUAL( buf[1], 0x03 );
+    CU_ASSERT_EQUAL( buf[2], 0x03 );
+    CU_ASSERT_EQUAL( buf[3], 0x04 );
+}
+
+static void test_iso_1_dirid()
+{
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("dir1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("dIR1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("DIR1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("dirwithbigname"), "DIRWITHB");
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("dirwith8"), "DIRWITH8");
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("dir.1"), "DIR_1");
+    CU_ASSERT_STRING_EQUAL( iso_1_dirid("4f<0KmM::xcvf"), "4F_0KMM_");
+}
+
+static void test_iso_2_dirid()
+{
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("dir1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("dIR1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("DIR1"), "DIR1" );
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("dirwithbigname"), "DIRWITHBIGNAME");
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("dirwith8"), "DIRWITH8");
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("dir.1"), "DIR_1");
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("4f<0KmM::xcvf"), "4F_0KMM__XCVF");
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("directory with 31 characters ok"), "DIRECTORY_WITH_31_CHARACTERS_OK");
+    CU_ASSERT_STRING_EQUAL( iso_2_dirid("directory with more than 31 characters"), "DIRECTORY_WITH_MORE_THAN_31_CHA");
+}
+
+static void test_iso_1_fileid()
+{
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("fILe1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("FILE1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid(".EXT"), ".EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.ext"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("fiLE.ext"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.EXt"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("FILE.EXT"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("bigfilename"), "BIGFILEN.");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("bigfilename.ext"), "BIGFILEN.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("bigfilename.e"), "BIGFILEN.E");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.bigext"), "FILE.BIG");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid(".bigext"), ".BIG");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("bigfilename.bigext"), "BIGFILEN.BIG");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file<:a.ext"), "FILE__A.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.<:a"), "FILE.__A");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file<:a.--a"), "FILE__A.__A");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.ex1.ex2"), "FILE_EX1.EX2");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("file.ex1.ex2.ex3"), "FILE_EX1.EX3");
+    CU_ASSERT_STRING_EQUAL( iso_1_fileid("fil.ex1.ex2.ex3"), "FIL_EX1_.EX3");
+}
+
+static void test_iso_2_fileid()
+{
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("fILe1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("FILE1"), "FILE1.");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid(".EXT"), ".EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.ext"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("fiLE.ext"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.EXt"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("FILE.EXT"), "FILE.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("bigfilename"), "BIGFILENAME.");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("bigfilename.ext"), "BIGFILENAME.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("bigfilename.e"), "BIGFILENAME.E");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("31 characters filename.extensio"), "31_CHARACTERS_FILENAME.EXTENSIO");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("32 characters filename.extension"), "32_CHARACTERS_FILENAME.EXTENSIO");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("more than 30 characters filename.extension"), "MORE_THAN_30_CHARACTERS_FIL.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.bigext"), "FILE.BIGEXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid(".bigext"), ".BIGEXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("bigfilename.bigext"), "BIGFILENAME.BIGEXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file<:a.ext"), "FILE__A.EXT");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.<:a"), "FILE.__A");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file<:a.--a"), "FILE__A.__A");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.ex1.ex2"), "FILE_EX1.EX2");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("file.ex1.ex2.ex3"), "FILE_EX1_EX2.EX3");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid("fil.ex1.ex2.ex3"), "FIL_EX1_EX2.EX3");
+    CU_ASSERT_STRING_EQUAL( iso_2_fileid(".file.bigext"), "_FILE.BIGEXT");
+}
+
 static void test_iso_rbtree_insert()
 {
     int res;
@@ -86,5 +185,10 @@ void add_util_suite()
 	
 	CU_add_test(pSuite, "div_up()", test_div_up);
 	CU_add_test(pSuite, "round_up()", test_round_up);
+    CU_add_test(pSuite, "iso_bb()", test_iso_bb);
+    CU_add_test(pSuite, "iso_1_dirid()", test_iso_1_dirid);
+    CU_add_test(pSuite, "iso_2_dirid()", test_iso_2_dirid);
+    CU_add_test(pSuite, "iso_1_fileid()", test_iso_1_fileid);
+    CU_add_test(pSuite, "iso_2_fileid()", test_iso_2_fileid);
     CU_add_test(pSuite, "iso_rbtree_insert()", test_iso_rbtree_insert);
 }