# File bigdecimal/lib/bigdecimal/math.rb, line 156 def log(x, prec) raise ArgumentError, "Zero or negative argument for log" if x <= 0 || prec <= 0 return x if x.infinite? || x.nan? one = BigDecimal("1") two = BigDecimal("2") n = prec + BigDecimal.double_fig x = (x - one).div(x + one,n) x2 = x.mult(x,n) y = x d = y i = one while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0) m = BigDecimal.double_fig if m < BigDecimal.double_fig x = x2.mult(x,n) i += two d = x.div(i,m) y += d end y*two end