phpjs/functions/bc/bcround.js

php.js offers community built php functions in javascript

function bcround(val, precision) {
  //  discuss at: http://phpjs.org/functions/bcround/
  // original by: lmeyrick (https://sourceforge.net/projects/bcmath-js/)
  //  depends on: _phpjs_shared_bc
  //   example 1: bcround(1, 2);
  //   returns 1: 3
  //        todo: implement these testcases

  var libbcmath = this._phpjs_shared_bc();

  var temp, result, digit;
  var right_operand;

  // create number
  temp = libbcmath.bc_init_num();
  temp = libbcmath.php_str2num(val.toString());

  // check if any rounding needs
  if (precision >= temp.n_scale) {
    // nothing to round, just add the zeros.
    while (temp.n_scale < precision) {
      temp.n_value[temp.n_len + temp.n_scale] = 0;
      temp.n_scale++;
    }
    return temp.toString();
  }

  // get the digit we are checking (1 after the precision)
  // loop through digits after the precision marker
  digit = temp.n_value[temp.n_len + precision];

  right_operand = libbcmath.bc_init_num();
  right_operand = libbcmath.bc_new_num(1, precision);

  if (digit >= 5) {
    //round away from zero by adding 1 (or -1) at the "precision".. ie 1.44999 @ 3dp = (1.44999 + 0.001).toString().substr(0,5)
    right_operand.n_value[right_operand.n_len + right_operand.n_scale - 1] = 1;
    if (temp.n_sign == libbcmath.MINUS) {
      // round down
      right_operand.n_sign = libbcmath.MINUS;
    }
    result = libbcmath.bc_add(temp, right_operand, precision);
  } else {
    // leave-as-is.. just truncate it.
    result = temp;
  }

  if (result.n_scale > precision) {
    result.n_scale = precision;
  }
  return result.toString();
}