function hex2b64(h) {
  var i;
  var c;
  var ret = "";
  for(i = 0; i+3 <= h.length; i+=3) {
    c = parseInt(h.substring(i,i+3),16);
    ret += b64map.charAt(c >> 6) + b64map.charAt(c & 63);
  }
  if(i+1 == h.length) {
    c = parseInt(h.substring(i,i+1),16);
    ret += b64map.charAt(c << 2);
  }
  else if(i+2 == h.length) {
    c = parseInt(h.substring(i,i+2),16);
    ret += b64map.charAt(c >> 2) + b64map.charAt((c & 3) << 4);
  }
  while((ret.length & 3) > 0) ret += b64pad;
  return ret;
}
set value by an ASN1Object
@name setString
@memberOf KJUR.asn1.DERTaggedObject
@function
@param {Boolean} isExplicitFlag flag for explicit/implicit tag
@param {Integer} tagNoHex hexadecimal string of ASN.1 tag
@param {ASN1Object} asn1Object ASN.1 to encapsulate