DCT encoding improvement

gistfile1.txt

const NEW_CHARMAP = "\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x20!\"#$%&'{([])}*+-.\\/0123456789:;,<=>?@EeAaUuOoIiFfGgHhJjLl|WwMmNnBbDdTtPpQqRrKkCcSsZzVvXxYy^_`~";
function get_new_char_code(old_char_code){
	return NEW_CHARMAP.indexOf(String.fromCharCode(old_char_code));
}
function get_old_char_code(new_char_code){
  return NEW_CHARMAP.charCodeAt(new_char_code);
}


function recalculate() {

  var in_text = document.getElementById('in').value,
      in_len  = in_text.length;

  /* Convert text to an array of ASCII values. */

  var in_buf = [];
  for (var i = 0; i < in_len; i++) in_buf.push(get_new_char_code(in_text.charCodeAt(i)));

  /* Run DCT. */

  var dct_result = dct(in_buf, in_len);

  /* Update text under slider. */

  var q_div = document.getElementById('div').value / 10;
  document.getElementById('slider_pos').innerText = q_div;

  /* Reduce precision. */

  dct_result = quantize(dct_result, in_len, q_div);

  /* Run inverse DCT. */

  var idct_result = idct(dct_result, in_len);

  /* Substitute unprintables. */

  for (var i = 0; i < in_len; i++){
	  idct_result[i] = get_old_char_code(idct_result[i]);
    if (idct_result[i] < 32 && idct_result[i] != 10) idct_result[i] = 63 /* ? */;
	}

  /* Write result, converting ASCII values to a string. */

  var out_text = String.fromCharCode.apply(null, idct_result);
  document.getElementById('out').value = out_text;

}

https://lcamtuf.substack.com/p/afternoon-project-jpeg-dct-text-lossifizer

https://lcamtuf.coredump.cx/lossifizer/