string.pod

SinFP是一种新的识别对方计算机操作系统类型的工具

=head1 NAME

Bit::Vector::String - Generic string import/export for Bit::Vector

=head1 SYNOPSIS

  use Bit::Vector::String;

  to_Oct
      $string = $vector->to_Oct();

  from_Oct
      $vector->from_Oct($string);

  new_Oct
      $vector = Bit::Vector->new_Oct($bits,$string);

  String_Export
      $string = $vector->String_Export($type);

  String_Import
      $type = $vector->String_Import($string);

  new_String
      $vector = Bit::Vector->new_String($bits,$string);
      ($vector,$type) = Bit::Vector->new_String($bits,$string);

=head1 DESCRIPTION

=over 2

=item *

C<$string = $vector-E<gt>to_Oct();>

Returns an octal string representing the given bit vector.

Note that this method is not particularly efficient, since it
is almost completely realized in Perl, and moreover internally
operates on a Perl list of individual octal digits which it
concatenates into the final string using "C<join('', ...)>".

A benchmark reveals that this method is about 40 times slower
than the method "C<to_Bin()>" (which is realized in C):

 Benchmark: timing 10000 iterations of to_Bin, to_Hex, to_Oct...
     to_Bin:  1 wallclock secs ( 1.09 usr +  0.00 sys =  1.09 CPU)
     to_Hex:  1 wallclock secs ( 0.53 usr +  0.00 sys =  0.53 CPU)
     to_Oct: 40 wallclock secs (40.16 usr +  0.05 sys = 40.21 CPU)

Note that since an octal digit is always worth three bits,
the length of the resulting string is always a multiple of
three bits, regardless of the true length (in bits) of the
given bit vector.

Also note that the B<LEAST> significant octal digit is
located at the B<RIGHT> end of the resulting string, and
the B<MOST> significant digit at the B<LEFT> end.

Finally, note that this method does B<NOT> prepend any uniquely
identifying format prefix (such as "0o") to the resulting string
(which means that the result of this method only contains valid
octal digits, i.e., [0-7]).

However, this can of course most easily be done as needed,
as follows:

  $string = '0o' . $vector->to_Oct();

=item *

C<$vector-E<gt>from_Oct($string);>

Allows to read in the contents of a bit vector from an octal string,
such as returned by the method "C<to_Oct()>" (see above).

Note that this method is not particularly efficient, since it is
almost completely realized in Perl, and moreover chops the input
string into individual characters using "C<split(//, $string)>".

Remember also that the least significant bits are always to the
right of an octal string, and the most significant bits to the left.
Therefore, the string is actually reversed internally before storing
it in the given bit vector using the method "C<Chunk_List_Store()>",
which expects the least significant chunks of data at the beginning
of a list.

A benchmark reveals that this method is about 40 times slower than
the method "C<from_Bin()>" (which is realized in C):

 Benchmark: timing 10000 iterations of from_Bin, from_Hex, from_Oct...
   from_Bin:  1 wallclock secs ( 1.13 usr +  0.00 sys =  1.13 CPU)
   from_Hex:  1 wallclock secs ( 0.80 usr +  0.00 sys =  0.80 CPU)
   from_Oct: 46 wallclock secs (44.95 usr +  0.00 sys = 44.95 CPU)

If the given string contains any character which is not an octal digit
(i.e., [0-7]), a fatal syntax error ensues ("unknown string type").

Note especially that this method does B<NOT> accept any uniquely
identifying format prefix (such as "0o") in the given string; the
presence of such a prefix will also lead to the fatal "unknown
string type" error.

If the given string contains less octal digits than are needed to
completely fill the given bit vector, the remaining (most significant)
bits all remain cleared (i.e., set to zero).

This also means that, even if the given string does not contain
enough digits to completely fill the given bit vector, the previous
contents of the bit vector are erased completely.

If the given string is longer than it needs to fill the given bit
vector, the superfluous characters are simply ignored.

This behaviour is intentional so that you may read in the string
representing one bit vector into another bit vector of different
size, i.e., as much of it as will fit.

=item *

C<$vector = Bit::Vector-E<gt>new_Oct($bits,$string);>

This method is an alternative constructor which allows you to create
a new bit vector object (with "C<$bits>" bits) and to initialize it
all in one go.

The method internally first calls the bit vector constructor method
"C<new()>" and then stores the given string in the newly created
bit vector using the same approach as the method "C<from_Oct()>"
(described above).

Note that this approach is not particularly efficient, since it
is almost completely realized in Perl, and moreover chops the input
string into individual characters using "C<split(//, $string)>".

An exception will be raised if the necessary memory cannot be allocated
(see the description of the method "C<new()>" in L<Bit::Vector(3)> for
possible causes) or if the given string cannot be converted successfully
(see the description of the method "C<from_Oct()>" above for details).

Note especially that this method does B<NOT> accept any uniquely
identifying format prefix (such as "0o") in the given string and that
such a prefix will lead to a fatal "unknown string type" error.

In case of an error, the memory occupied by the new bit vector is
released again before the exception is actually thrown.

If the number of bits "C<$bits>" given has the value "C<undef>",
the method will automatically allocate a bit vector with a size
(i.e., number of bits) of three times the length of the given string
(since every octal digit is worth three bits).

Note that this behaviour is different from that of the methods
"C<new_Hex()>", "C<new_Bin()>", "C<new_Dec()>" and "C<new_Enum()>"
(which are realized in C, internally); these methods will silently
assume a value of 0 bits if "C<undef>" is given (and may warn
about the "Use of uninitialized value" if warnings are enabled).

=item *

C<$string = $vector-E<gt>String_Export($type);>

Returns a string representing the given bit vector in the
format specified by "C<$type>":

  1 | b | bin      =>  binary        (using "to_Bin()")
  2 | o | oct      =>  octal         (using "to_Oct()")
  3 | d | dec      =>  decimal       (using "to_Dec()")
  4 | h | hex | x  =>  hexadecimal   (using "to_Hex()")
  5 | e | enum     =>  enumeration   (using "to_Enum()")
  6 | p | pack     =>  packed binary (using "Block_Read()")

The case (lower/upper/mixed case) of "C<$type>" is ignored.

If "C<$type>" is omitted or "C<undef>" or false ("0"
or the empty string), a hexadecimal string is returned
as the default format.

If "C<$type>" does not have any of the values described
above, a fatal "unknown string type" will occur.

Beware that in order to guarantee that the strings can
be correctly parsed and read in by the methods
"C<String_Import()>" and "C<new_String()>" (described
below), the method "C<String_Export()>" provides
uniquely identifying prefixes (and, in one case,
a suffix) as follows:

  1 | b | bin      =>  '0b' . $vector->to_Bin();
  2 | o | oct      =>  '0o' . $vector->to_Oct();
  3 | d | dec      =>         $vector->to_Dec(); # prefix is [+-]
  4 | h | hex | x  =>  '0x' . $vector->to_Hex();
  5 | e | enum     =>  '{'  . $vector->to_Enum() . '}';
  6 | p | pack     =>  ':'  . $vector->Size() .
                       ':'  . $vector->Block_Read();

This is necessary because certain strings can be valid
representations in more than one format.

All strings in binary format, i.e., which only contain "0"
and "1", are also valid number representations (of a different
value, of course) in octal, decimal and hexadecimal.

Likewise, a string in octal format is also valid in decimal
and hexadecimal, and a string in decimal format is also valid
in hexadecimal.

Moreover, if the enumeration of set bits (as returned by
"C<to_Enum()>") only contains one element, this element could
be mistaken for a representation of the entire bit vector
(instead of just one bit) in decimal.

Beware also that the string returned by format "6" ("packed
binary") will in general B<NOT BE PRINTABLE>, because it will
usually consist of many unprintable characters!

=item *

C<$type = $vector-E<gt>String_Import($string);>

Allows to read in the contents of a bit vector from a string
which has previously been produced by "C<String_Export()>",
"C<to_Bin()>", "C<to_Oct()>", "C<to_Dec()>", "C<to_Hex()>",
"C<to_Enum()>", "C<Block_Read()>" or manually or by another
program.

Beware however that the string must have the correct format;
otherwise a fatal "unknown string type" error will occur.

The correct format is the one returned by "C<String_Export()>"
(see immediately above).

The method will also try to automatically recognize formats
without identifying prefix such as returned by the methods
"C<to_Bin()>", "C<to_Oct()>", "C<to_Dec()>", "C<to_Hex()>"
and "C<to_Enum()>".

However, as explained above for the method "C<String_Export()>",
due to the fact that a string may be a valid representation in
more than one format, this may lead to unwanted results.

The method will try to match the format of the given string
in the following order:

If the string consists only of [01], it will be considered
to be in binary format (although it could be in octal, decimal
or hexadecimal format or even be an enumeration with only
one element as well).

If the string consists only of [0-7], it will be considered
to be in octal format (although it could be in decimal or
hexadecimal format or even be an enumeration with only
one element as well).

If the string consists only of [0-9], it will be considered
to be in decimal format (although it could be in hexadecimal
format or even be an enumeration with only one element as well).

If the string consists only of [0-9A-Fa-f], it will be considered
to be in hexadecimal format.

If the string only contains numbers in decimal format, separated
by commas (",") or dashes ("-"), it is considered to be an
enumeration (a single decimal number also qualifies).

And if the string starts with ":[0-9]:", the remainder of the
string is read in with "C<Block_Store()>".

To avoid misinterpretations, it is therefore recommendable to
always either use the method "C<String_Export()>" or to provide
some uniquely identifying prefix (and suffix, in one case)
yourself:

  binary         =>  '0b' . $string;
  octal          =>  '0o' . $string;
  decimal        =>  '+'  . $string; # in case "$string"
                 =>  '-'  . $string; # has no sign yet
  hexadecimal    =>  '0x' . $string;
                 =>  '0h' . $string;
  enumeration    =>  '{'  . $string . '}';
                 =>  '['  . $string . ']';
                 =>  '<'  . $string . '>';
                 =>  '('  . $string . ')';
  packed binary  =>  ':'  . $vector->Size() .
                     ':'  . $vector->Block_Read();

Note that case (lower/upper/mixed case) is not important
and will be ignored by this method.

Internally, the method uses the methods "C<from_Bin()>",
"C<from_Oct()>", "C<from_Dec()>", "C<from_Hex()>",
"C<from_Enum()>" and "C<Block_Store()>" for actually
importing the contents of the string into the given
bit vector. See their descriptions here in this document
and in L<Bit::Vector(3)> for any further conditions that
must be met and corresponding possible fatal error messages.

The method returns the number of the format that has been
recognized:

                1    =>    binary
                2    =>    octal
                3    =>    decimal
                4    =>    hexadecimal
                5    =>    enumeration
                6    =>    packed binary

=item *

C<$vector = Bit::Vector-E<gt>new_String($bits,$string);>

C<($vector,$type) = Bit::Vector-E<gt>new_String($bits,$string);>

This method is an alternative constructor which allows you to create
a new bit vector object (with "C<$bits>" bits) and to initialize it
all in one go.

The method internally first calls the bit vector constructor method
"C<new()>" and then stores the given string in the newly created
bit vector using the same approach as the method "C<String_Import()>"
(described immediately above).

An exception will be raised if the necessary memory cannot be allocated
(see the description of the method "C<new()>" in L<Bit::Vector(3)> for
possible causes) or if the given string cannot be converted successfully
(see the description of the method "C<String_Import()>" above for details).

In case of an error, the memory occupied by the new bit vector is
released again before the exception is actually thrown.

If the number of bits "C<$bits>" given has the value "C<undef>", the
method will automatically determine this value for you and allocate
a bit vector of the calculated size.

Note that this behaviour is different from that of the methods
"C<new_Hex()>", "C<new_Bin()>", "C<new_Dec()>" and "C<new_Enum()>"
(which are realized in C, internally); these methods will silently
assume a value of 0 bits if "C<undef>" is given (and may warn
about the "Use of uninitialized value" if warnings are enabled).

The necessary number of bits is calculated as follows:

  binary         =>       length($string);
  octal          =>   3 * length($string);
  decimal        =>  int( length($string) * log(10) / log(2) + 1 );
  hexadecimal    =>   4 * length($string);
  enumeration    =>  maximum of values found in $string + 1
  packed binary  =>  $string =~ /^:(\d+):/;

If called in scalar context, the method returns the newly created
bit vector object.

If called in list context, the method additionally returns the
number of the format which has been recognized, as explained
above for the method "C<String_Import()>".

=back

=head1 SEE ALSO

Bit::Vector(3), Bit::Vector::Overload(3).

=head1 VERSION

This man page documents "Bit::Vector::String" version 6.4.

=head1 AUTHOR

  Steffen Beyer
  mailto:[e-mail]
  http://www.engelschall.com/u/sb/download/

=head1 COPYRIGHT

Copyright (c) 2004 by Steffen Beyer. All rights reserved.

=head1 LICENSE

This package is free software; you can redistribute it and/or
modify it under the same terms as Perl itself, i.e., under the
terms of the "Artistic License" or the "GNU General Public License".

The C library at the core of this Perl module can additionally
be redistributed and/or modified under the terms of the "GNU
Library General Public License".

Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
"GNU_LGPL.txt" in this distribution for details!

=head1 DISCLAIMER

This package is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the "GNU General Public License" for more details.