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

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This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
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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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