Convert binary buffer object SID to string

sid.js

/*
# Convert binary encoded object SID to a string 
# (eg. S-1-5-21-1004336348-1177238915-682003330-512)
#
# SID format: https://technet.microsoft.com/en-us/library/cc962011.aspx 
#
# ldapjs `searchEntry` has attribute `raw` that holds the raw
# values, including the `objectSid` buffer when one exists. Pass that
# buffer to get the string representation that can then be easily
# used in LDAP search filters, for example.
#
*/

let pad = function(s) { if (s.length < 2) { return `0${s}`; } else { return s; } };

let sidBufferToString = function(buf) {
  let asc, end;
  let i;
  if (buf == null) { return null; }

  let version             = buf[0];
  let subAuthorityCount   = buf[1];
  let identifierAuthority = parseInt(((() => {
    let result = [];
    for (i = 2; i <= 7; i++) {
      result.push(buf[i].toString(16));
    }
    return result;
  })()).join(''), 16);

  let sidString = `S-${version}-${identifierAuthority}`;

  for (i = 0, end = subAuthorityCount-1, asc = 0 <= end; asc ? i <= end : i >= end; asc ? i++ : i--) {
    let subAuthOffset = i * 4;
    let tmp =
      pad(buf[11 + subAuthOffset].toString(16)) +
      pad(buf[10 + subAuthOffset].toString(16)) +
      pad(buf[9  + subAuthOffset].toString(16)) +
      pad(buf[8  + subAuthOffset].toString(16));
    sidString += `-${parseInt(tmp, 16)}`;
  }

  return sidString;
};