diff --git a/src/util.c b/src/util.c
index b7ab0a4..803fcd4 100644
--- a/src/util.c
+++ b/src/util.c
@@ -15,6 +15,7 @@
 #include <iconv.h>
 #include <string.h>
 #include <errno.h>
+#include <ctype.h>
 
 int div_up(int n, int div)
 {
@@ -176,3 +177,103 @@ int str2ascii(const char *icharset, const char *input, char **output)
     return ISO_SUCCESS;
 }
 
+static int valid_d_char(char c)
+{
+    return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c == '_');
+}
+
+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';
+}
diff --git a/src/util.h b/src/util.h
index 9c77a71..93dc390 100644
--- a/src/util.h
+++ b/src/util.h
@@ -13,6 +13,49 @@ extern inline int div_up(int n, int div);
 
 extern inline int round_up(int n, int mul);
 
+/**
+ * Convert a given string from any input charset to ASCII
+ * 
+ * @param icharset
+ *      Input charset. Must be supported by iconv
+ * @param input
+ *      Input string
+ * @param ouput
+ *      Location where the pointer to the ouput string will be stored
+ * @return
+ *      1 on success, < 0 on error
+ */
 int str2ascii(const char *icharset, const char *input, char **output);
 
+/**
+ * Ensure a given string is a valid ISO directory identifier, modifying
+ * it if needed.
+ * 
+ * @param src
+ *      The identifier, in ASCII encoding. It may be modified by the function.
+ * @param maxlen
+ *      Maximum length supported by current iso level.
+ */
+void iso_dirid(char *src, int maxlen);
+
+/**
+ * Ensure a given string is a valid ISO level 1 file identifier, in 8.3 
+ * format, modifying it if needed.
+ * 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.
+ */
+void iso_1_fileid(char *src);
+
+/**
+ * Ensure a given string is a valid ISO level 2 file identifier, modifying it
+ * if needed.
+ * 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.
+ */
+void iso_2_fileid(char *src);
+
 #endif /*LIBISO_UTIL_H_*/