+ * ulong ul2int ULONG => INT can fail if >INT_MAX
+ * ulong int2ul INT => ULONG can fail if <0
+ * ulong mask A B => A & B
+ * ulong add A B => A + B (mod 2^32)
+ * ulong subtract A B => A - B (mod 2^32)
+ * ulong compare A B => 0 -1 (A<B) +1 (A>B)
+ * ulong shift l|r ULONG BITS fails if BITS >32
+ *
+ * ulong ul2bitfields VALUE [SIZE TYPE [TYPE-ARG...] ...] => 0/1
+ * ulong bitfields2ul BASE [SIZE TYPE [TYPE-ARG...] ...] => ULONG
+ * goes from left (MSbit) to right (LSbit) where
+ * SIZE is size in bits
+ * TYPE [TYPE-ARGS...] is as below
+ * zero
+ * ignore
+ * fixed ULONG-VALUE
+ * uint VARNAME/VALUE (VARNAME if ul2bitfields;
+ * ulong VARNAME/VALUE VALUE if bitfields2ul)
+ *
+ * Address ranges (addrmap.c):
+ *
+ * An address range is a slightly efficient partial mapping from
+ * addresses to arbitrary data values. An address is a number of
+ * octets expressed as an hbytes. All the addresses covered by the
+ * same addrmap should have the same length.
+ *
+ * hbytes addr-map lookup MAP-VAR ADDRESS [DEFAULT] => DATA
+ * Error on missing default or if any prefix longer than ADDRESS.
+ *
+ * hbytes addr-map amend-range MAP-VAR START END DATA
+ * hbytes addr-map amend-mask MAP-VAR PREFIX PREFIX-LENGTH DATA
+ * Sets all of the addresses in PREFIX/PREFIX-LENGTH to the
+ * relevant value.
+ *
+ * Representation:
+ * An address map MAP is
+ * [list BIT-LENGTH \
+ * [list START END DATA-VALUE] \
+ * [list START' END' DATA-VALUE'] \
+ * ...
+ * ]
+ * The list is sorted by ascending START and entries do not overlap.
+ * START and END are both inclusive. BIT-LENGTH is in usual Tcl
+ * integer notation and must be a multiple of 8.
+ *
+ * Error codes
+ *
+ * HBYTES BLOCKCIPHER CRYPTFAIL CRYPT block cipher mode failed somehow (!)
+ * HBYTES BLOCKCIPHER CRYPTFAIL MAC HMAC failed somehow (!)
+ * HBYTES BLOCKCIPHER LENGTH block cipher input has unsuitable length
+ * HBYTES BLOCKCIPHER PARAMS key or iv not suitable
+ * HBYTES HMAC PARAMS key, input or output size not suitable
+ * HBYTES LENGTH OVERRUN block too long
+ * HBYTES LENGTH RANGE input length or offset is -ve or silly
+ * HBYTES LENGTH UNDERRUN block too short (or offset too big)
+ * HBYTES LENGTH MISMATCH when blocks must be exactly same length
+ * HBYTES SYNTAX supposed hex block had wrong syntax
+ * HBYTES VALUE OVERFLOW value to be conv'd to hex too big/long
+ * HBYTES ADDRMAP NOMATCH no addr/mask matches address for lookup
+ * HBYTES ADDRMAP UNDERRUN addr for lookup or amend is too short
+ * HBYTES ADDRMAP OVERRUN addr for lookup or amend is too long
+ * HBYTES ADDRMAP EXCLBITS amend-mask 1-bits outside prefix len
+ * HBYTES ADDRMAP BADRANGE amend-range start > end
+ * HBYTES ADDRMAP VALUE addr-map string value is erroneous
+ * SOCKADDR AFUNIX LENGTH path for AF_UNIX socket too long
+ * SOCKADDR SYNTAX IPV4 bad IPv4 socket address &/or port
+ * SOCKADDR SYNTAX OTHER bad socket addr, couldn't tell what kind
+ * ULONG BITCOUNT NEGATIVE -ve bitcount specified where not allowed
+ * ULONG BITCOUNT OVERRUN attempt to use more than 32 bits
+ * ULONG BITCOUNT UNDERRUN bitfields add up to less than 32
+ * ULONG VALUE NEGATIVE attempt convert -ve integers to ulong
+ * ULONG VALUE OVERFLOW converted value does not fit in result
+ * TUNTAP IFNAME LENGTH tun/tap interface name too long
+ * TUNTAP MTU OVERRUN tun/tap mtu limited to 2^16 bytes
+ *
+ * Refs: HMAC: RFC2104 */