convert_ldaptime_to_unixepoch

# A shell conversion of
# https://gist.github.com/caseydunham/508e2994e1195e4cb8e4
convert_ldaptime_to_unixepoch() {
  local ldap_offset ldap_timestamp
  ldap_timestamp="${1:?No ldap timestamp supplied}"
  ldap_timestamp=$(( ldap_timestamp / 10000000 ))
  # Calculated as '( (1970-1601) * 365 -3 + ((1970-1601)/4) ) * 86400'
  ldap_offset=11644473600
  printf -- '%s\n' "$(( ldap_timestamp - ldap_offset ))"
}