It seems like a vestige of ext/md5.

g -L frozen_string_literal ext/**/*.rb|xargs ruby -Ka -e'ARGV.each{|fn|puts
fn;open(fn,"r+"){|f|s=f.read.sub(/\A(#!.*\n)?(#.*coding.*\n)?/,"\\&#
frozen_string_literal: false\n");f.rewind;f.write s}}'

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53143 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

  includeing ext/digest/extconf.h. [Bug #3231]
  https://msdn.microsoft.com/library/36k2cdd4.aspx

* ext/digest/*/extconf.rb: remove ext/digest from include search path
  to avoid confusion of cl.exe.

* ext/digest/*/*.[ch]: explicitly specify def.h's path.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52694 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

  rb_ to avoid name clash in writing extensions.

* ext/digest: Introduce Digest::Class and Digest::Instance for
  ease of implementing subclasses and add-ons, inspried by
  gotoyuzo.

* ext/digest: The Digest::Instance module now requires and assumes
  that any instance be resettable and clonable, and add some
  convenient instance methods such as "new()", for creating a new
  copy, parameter taking "digest()" and "hexdigest()", for instant
  calculation.  These methods make digest instances work just like
  digest classes.

* ext/digest/sha2/lib/digest/sha2.rb:
  Add the Digest::SHA2 class to wrap up SHA2 variants: SHA256,
  SHA384 and SHA512, hoping this module would make a decent
  example of a digest subclass written in Ruby.

* ext/digest/lib/digest.rb: Adjust autoload entries for SHA2
  classes.

* ext/digest/lib/digest/hmac.rb: Follow the framework updates.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@11197 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

  support out of the base class and have a separate module named
  digest/bubblebabble.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@11152 b2dd03c8-39d4-4d8f-98ff-823fe69b080e