=over 8

=item I<binary>

This is the most compact form, but it is not well suited for printing
or embedding in places that can't handle arbitrary data.

=item I<hex>

A twice as long string of lowercase hexadecimal digits.

=item I<base64>

A string of portable printable characters.  This is the base64 encoded
representation of the digest with any trailing padding removed.  The
string will be about 30% longer than the binary version.
L<MIME::Base64> tells you more about this encoding.

=back


The functional interface is simply importable functions with the same
name as the algorithm.  The functions take the message as argument and
return the digest.  Example:

  use Digest::MD5 qw(md5);
  $digest = md5($message);

There are also versions of the functions with "_hex" or "_base64"
appended to the name, which returns the digest in the indicated form.

=head1 OO INTERFACE

The following methods are available for all C<Digest::> modules:

=over 4

=item $ctx = Digest->XXX($arg,...)

=item $ctx = Digest->new(XXX => $arg,...)

=item $ctx = Digest::XXX->new($arg,...)

The constructor returns some object that encapsulate the state of the
message-digest algorithm.  You can add data to the object and finally
ask for the digest.  The "XXX" should of course be replaced by the proper
name of the digest algorithm you want to use.

The two first forms are simply syntactic sugar which automatically
load the right module on first use.  The second form allow you to use
algorithm names which contains letters which are not legal perl
identifiers, e.g. "SHA-1".  If no implementation for the given algorithm
can be found, then an exception is raised.

If new() is called as an instance method (i.e. $ctx->new) it will just
reset the state the object to the state of a newly created object.  No
new object is created in this case, and the return value is the
reference to the object (i.e. $ctx).

=item $other_ctx = $ctx->clone

The clone method creates a copy of the digest state object and returns
a reference to the copy.

=item $ctx->reset

This is just an alias for $ctx->new.

=item $ctx->add( $data, ... )

The $data provided as argument are appended to the message we
calculate the digest for.  The return value is the $ctx object itself.

=item $ctx->addfile( $io_handle )

The $io_handle is read until EOF and the content is appended to the
message we calculate the digest for.  The return value is the $ctx
object itself.

=item $ctx->add_bits( $data, $nbits )

=item $ctx->add_bits( $bitstring )

The bits provided are appended to the message we calculate the digest
for.  The return value is the $ctx object itself.

The two argument form of add_bits() will add the first $nbits bits
from data.  For the last potentially partial byte only the high order
C<< $nbits % 8 >> bits are used.  If $nbits is greater than C<<
length($data) * 8 >>, then this method would do the same as C<<
$ctx->add($data) >>, that is $nbits is silently ignored.

The one argument form of add_bits() takes a $bitstring of "1" and "0"
chars as argument.  It's a shorthand for C<< $ctx->add_bits(pack("B*",
$bitstring), length($bitstring)) >>.

This example shows two calls that should have the same effect:

   $ctx->add_bits("111100001010");