* bignum.c (LOG2_KARATSUBA_BIG2STR_DIGITS): Removed.
  (KARATSUBA_BIG2STR_DIGITS): Removed.
  (big2str_numdigits_cache): New variable.
  (power_cache_get_power): Merged with power_cache_get_power0.
  This function returns maxpow_in_bdigit_dbl(base)**(2**power_level).
  (rb_big2str1): use power_cache_get_power.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42295 b2dd03c8-39d4-4d8f-98ff-823fe69b080e