add error_table_name

git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@4835 ec53bebd-3082-4978-b11e-865c3cabbd6b

lib/com_err/com_err.c

@@ -135,3 +135,33 @@ reset_com_err_hook (void)
 {
     return set_com_err_hook(NULL);
 }
+
+#define ERRCODE_RANGE   8       /* # of bits to shift table number */
+#define BITS_PER_CHAR   6       /* # bits to shift per character in name */
+
+static const char char_set[] =
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_";
+
+static char buf[6];
+
+const char *
+error_table_name(int num)
+{
+    int ch;
+    int i;
+    char *p;
+
+    /* num = aa aaa abb bbb bcc ccc cdd ddd d?? ??? ??? */
+    p = buf;
+    num >>= ERRCODE_RANGE;
+    /* num = ?? ??? ??? aaa aaa bbb bbb ccc ccc ddd ddd */
+    num &= 077777777;
+    /* num = 00 000 000 aaa aaa bbb bbb ccc ccc ddd ddd */
+    for (i = 4; i >= 0; i--) {
+        ch = (num >> BITS_PER_CHAR * i) & ((1 << BITS_PER_CHAR) - 1);
+        if (ch != 0)
+            *p++ = char_set[ch-1];
+    }
+    *p = '\0';
+    return(buf);
+}