* hbytes overwrite VAR START VALUE
* hbytes trimleft VAR removes any leading 0 octets
* hbytes repeat VALUE COUNT => COUNT copies of VALUE
+ * hbytes zeroes COUNT => COUNT zero bytes
+ * hbytes random COUNT => COUNT random bytes
+ * hbytes xor VAR VALUE $VAR (+)= VALUE
*
* hbytes ushort2h LONG => LONG must be <2^16, returns as hex
* hbytes h2ushort HEX => |HEX| must be 2 bytes, returns as ulong
* 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
*/