function quoted_printable_decode (str) {
  // http://kevin.vanzonneveld.net
  // +   original by: Ole Vrijenhoek
  // +   bugfixed by: Brett Zamir (http://brett-zamir.me)
  // +   reimplemented by: Theriault
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Theriault
  // *     example 1: quoted_printable_decode('a=3Db=3Dc');
  // *     returns 1: 'a=b=c'
  // *     example 2: quoted_printable_decode('abc  =20\r\n123  =20\r\n');
  // *     returns 2: 'abc   \r\n123   \r\n'
  // *     example 3: quoted_printable_decode('012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n56789');
  // *     returns 3: '01234567890123456789012345678901234567890123456789012345678901234567890123456789'
  // *    example 4: quoted_printable_decode("Lorem ipsum dolor sit amet=23, consectetur adipisicing elit");
  // *    returns 4: Lorem ipsum dolor sit amet#, consectetur adipisicing elit
  // Removes softline breaks
  var RFC2045Decode1 = /=\r\n/gm,
    // Decodes all equal signs followed by two hex digits
    RFC2045Decode2IN = /=([0-9A-F]{2})/gim,
    // the RFC states against decoding lower case encodings, but following apparent PHP behavior
    // RFC2045Decode2IN = /=([0-9A-F]{2})/gm,
    RFC2045Decode2OUT = function (sMatch, sHex) {
      return String.fromCharCode(parseInt(sHex, 16));
    };
  return str.replace(RFC2045Decode1, '').replace(RFC2045Decode2IN, RFC2045Decode2OUT);
}

quoted_printable_decode('a=3Db=3Dc');

'a=b=c'

quoted_printable_decode('abc  =20\r\n123  =20\r\n');

'abc   \r\n123   \r\n'

quoted_printable_decode('012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n56789');

'01234567890123456789012345678901234567890123456789012345678901234567890123456789'