Name 0.3010299956639812 as lg2

Co-authored-by: Kenta Murata <3959+mrkn@users.noreply.github.com>

Author: tompng

lib/bigdecimal.rb

@@ -193,7 +193,8 @@ def self.log(x, prec)
     # https://github.com/ruby/bigdecimal/pull/343
     sqrt_steps /= 10
 
-    prec2 = prec + [-x_minus_one_exponent, 0].max + (sqrt_steps * 0.3010299956639812).ceil
+    lg2 = 0.3010299956639812
+    prec2 = prec + [-x_minus_one_exponent, 0].max + (sqrt_steps * lg2).ceil
 
     sqrt_steps.times do
       x = x.sqrt(prec2)