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diff --git a/ext/digest/lib/digest/sha2.rb b/ext/digest/lib/digest/sha2.rb
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+++ b/ext/digest/lib/digest/sha2.rb
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+# frozen_string_literal: false
+#--
+# sha2.rb - defines Digest::SHA2 class which wraps up the SHA256,
+#           SHA384, and SHA512 classes.
+#++
+# Copyright (c) 2006 Akinori MUSHA <knu@iDaemons.org>
+#
+# All rights reserved.  You can redistribute and/or modify it under the same
+# terms as Ruby.
+#
+#   $Id$
+
+require 'digest'
+require 'digest/sha2/loader'
+
+module Digest
+  #
+  # A meta digest provider class for SHA256, SHA384 and SHA512.
+  #
+  # FIPS 180-2 describes SHA2 family of digest algorithms. It defines
+  # three algorithms:
+  # * one which works on chunks of 512 bits and returns a 256-bit
+  #   digest (SHA256),
+  # * one which works on chunks of 1024 bits and returns a 384-bit
+  #   digest (SHA384),
+  # * and one which works on chunks of 1024 bits and returns a 512-bit
+  #   digest (SHA512).
+  #
+  # ==Examples
+  #  require 'digest'
+  #
+  #  # Compute a complete digest
+  #  Digest::SHA2.hexdigest 'abc'          # => "ba7816bf8..."
+  #  Digest::SHA2.new(256).hexdigest 'abc' # => "ba7816bf8..."
+  #  Digest::SHA256.hexdigest 'abc'        # => "ba7816bf8..."
+  #
+  #  Digest::SHA2.new(384).hexdigest 'abc' # => "cb00753f4..."
+  #  Digest::SHA384.hexdigest 'abc'        # => "cb00753f4..."
+  #
+  #  Digest::SHA2.new(512).hexdigest 'abc' # => "ddaf35a19..."
+  #  Digest::SHA512.hexdigest 'abc'        # => "ddaf35a19..."
+  #
+  #  # Compute digest by chunks
+  #  sha2 = Digest::SHA2.new               # =>#<Digest::SHA2:256>
+  #  sha2.update "ab"
+  #  sha2 << "c"                           # alias for #update
+  #  sha2.hexdigest                        # => "ba7816bf8..."
+  #
+  #  # Use the same object to compute another digest
+  #  sha2.reset
+  #  sha2 << "message"
+  #  sha2.hexdigest                        # => "ab530a13e..."
+  #
+  class SHA2 < Digest::Class
+    # call-seq:
+    #   Digest::SHA2.new(bitlen = 256) -> digest_obj
+    #
+    # Create a new SHA2 hash object with a given bit length.
+    #
+    # Valid bit lengths are 256, 384 and 512.
+    def initialize(bitlen = 256)
+      case bitlen
+      when 256
+        @sha2 = Digest::SHA256.new
+      when 384
+        @sha2 = Digest::SHA384.new
+      when 512
+        @sha2 = Digest::SHA512.new
+      else
+        raise ArgumentError, "unsupported bit length: %s" % bitlen.inspect
+      end
+      @bitlen = bitlen
+    end
+
+    # call-seq:
+    #   digest_obj.reset -> digest_obj
+    #
+    # Reset the digest to the initial state and return self.
+    def reset
+      @sha2.reset
+      self
+    end
+
+    # call-seq:
+    #   digest_obj.update(string) -> digest_obj
+    #   digest_obj << string -> digest_obj
+    #
+    # Update the digest using a given _string_ and return self.
+    def update(str)
+      @sha2.update(str)
+      self
+    end
+    alias << update
+
+    def finish # :nodoc:
+      @sha2.digest!
+    end
+    private :finish
+
+
+    # call-seq:
+    #   digest_obj.block_length -> Integer
+    #
+    # Return the block length of the digest in bytes.
+    #
+    #   Digest::SHA256.new.block_length * 8
+    #   # => 512
+    #   Digest::SHA384.new.block_length * 8
+    #   # => 1024
+    #   Digest::SHA512.new.block_length * 8
+    #   # => 1024
+    def block_length
+      @sha2.block_length
+    end
+
+    # call-seq:
+    #   digest_obj.digest_length -> Integer
+    #
+    # Return the length of the hash value (the digest) in bytes.
+    #
+    #   Digest::SHA256.new.digest_length * 8
+    #   # => 256
+    #   Digest::SHA384.new.digest_length * 8
+    #   # => 384
+    #   Digest::SHA512.new.digest_length * 8
+    #   # => 512
+    #
+    # For example, digests produced by Digest::SHA256 will always be 32 bytes
+    # (256 bits) in size.
+    def digest_length
+      @sha2.digest_length
+    end
+
+    def initialize_copy(other) # :nodoc:
+      @sha2 = other.instance_eval { @sha2.clone }
+    end
+
+    def inspect # :nodoc:
+      "#<%s:%d %s>" % [self.class.name, @bitlen, hexdigest]
+    end
+  end
+end