exp

# File ext/bigdecimal/lib/bigdecimal/math.rb, line 156
  def exp(x, prec)
    raise ArgumentError, "Zero or negative precision for exp" if prec <= 0
    return BigDecimal("NaN") if x.infinite? || x.nan?
    n    = prec + BigDecimal.double_fig
    one  = BigDecimal("1")
    x = -x if neg = x < 0
    x1 = one
    y  = one
    d  = y
    z  = one
    i  = 0
    while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
      m = BigDecimal.double_fig if m < BigDecimal.double_fig
      x1  = x1.mult(x,n)
      i += 1
      z *= i
      d  = x1.div(z,m)
      y += d
    end
    if neg
      one.div(y, prec)
    else
      y.round(prec - y.exponent)
    end
  end