FAQ 4.5 How do I convert between numeric representations/bases/radixes?


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PerlFAQ Server

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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4.5: How do I convert between numeric representations/bases/radixes?

As always with Perl there is more than one way to do it. Below are a few
examples of approaches to making common conversions between number
representations. This is intended to be representational rather than
exhaustive.

Some of the examples later in perlfaq4 use the "Bit::Vector" module from
CPAN. The reason you might choose "Bit::Vector" over the perl built in
functions is that it works with numbers of ANY size, that it is
optimized for speed on some operations, and for at least some
programmers the notation might be familiar.

How do I convert hexadecimal into decimal
Using perl's built in conversion of "0x" notation:

$dec = 0xDEADBEEF;

Using the "hex" function:

$dec = hex("DEADBEEF");

Using "pack":

$dec = unpack("N", pack("H8", substr("0" x 8 . "DEADBEEF", -8)));

Using the CPAN module "Bit::Vector":

use Bit::Vector;
$vec = Bit::Vector->new_Hex(32, "DEADBEEF");
$dec = $vec->to_Dec();

How do I convert from decimal to hexadecimal
Using "sprintf":

$hex = sprintf("%X", 3735928559); # upper case A-F
$hex = sprintf("%x", 3735928559); # lower case a-f

Using "unpack":

$hex = unpack("H*", pack("N", 3735928559));

Using "Bit::Vector":

use Bit::Vector;
$vec = Bit::Vector->new_Dec(32, -559038737);
$hex = $vec->to_Hex();

And "Bit::Vector" supports odd bit counts:

use Bit::Vector;
$vec = Bit::Vector->new_Dec(33, 3735928559);
$vec->Resize(32); # suppress leading 0 if unwanted
$hex = $vec->to_Hex();

How do I convert from octal to decimal
Using Perl's built in conversion of numbers with leading zeros:

$dec = 033653337357; # note the leading 0!

Using the "oct" function:

$dec = oct("33653337357");

Using "Bit::Vector":

use Bit::Vector;
$vec = Bit::Vector->new(32);
$vec->Chunk_List_Store(3, split(//, reverse "33653337357"));
$dec = $vec->to_Dec();

How do I convert from decimal to octal
Using "sprintf":

$oct = sprintf("%o", 3735928559);

Using "Bit::Vector":

use Bit::Vector;
$vec = Bit::Vector->new_Dec(32, -559038737);
$oct = reverse join('', $vec->Chunk_List_Read(3));

How do I convert from binary to decimal
Perl 5.6 lets you write binary numbers directly with the "0b"
notation:

$number = 0b10110110;

Using "oct":

my $input = "10110110";
$decimal = oct( "0b$input" );

Using "pack" and "ord":

$decimal = ord(pack('B8', '10110110'));

Using "pack" and "unpack" for larger strings:

$int = unpack("N", pack("B32",
substr("0" x 32 . "11110101011011011111011101111", -32)));
$dec = sprintf("%d", $int);

# substr() is used to left pad a 32 character string with zeros.

Using "Bit::Vector":

$vec = Bit::Vector->new_Bin(32, "11011110101011011011111011101111");
$dec = $vec->to_Dec();

How do I convert from decimal to binary
Using "sprintf" (perl 5.6+):

$bin = sprintf("%b", 3735928559);

Using "unpack":

$bin = unpack("B*", pack("N", 3735928559));

Using "Bit::Vector":

use Bit::Vector;
$vec = Bit::Vector->new_Dec(32, -559038737);
$bin = $vec->to_Bin();

The remaining transformations (e.g. hex -> oct, bin -> hex, etc.)
are left as an exercise to the inclined reader.



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The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.
 
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