code: func (e *Encoding) DecodeToBigInt(s string) *big.Int {
  	var (
  		n = new(big.Int)
  
  		c     = new(big.Int)
  		idx   = new(big.Int)
  		power = new(big.Int)
  		exp   = new(big.Int)
  		bse   = new(big.Int)
  	)
  	bse.SetInt64(base)
  
  	// Run through each character to decode
  	for i, v := range s {
  		// Get index/position of the rune as a big int
  		idx.SetInt64(int64(strings.IndexRune(e.encode, v)))
  
  		// Work downwards through exponents
  		exp.SetInt64(int64(len(s) - (i + 1)))
  
  		// Calculate power for this exponent
  		power.Exp(bse, exp, nil)
  
  		// Multiplied by our index, gives us the value for this character
  		c = c.Mul(idx, power)
  
  		// Finally add to running total
  		n.Add(n, c)
  	}
  
  	return n
  }
docs: // DecodeToBigInt returns an arbitrary precision integer from the base62 encoded string