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

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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 below 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:

Using the hex function:

Using pack:

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

Using the CPAN module Bit::Vector:

use Bit::Vector;
\$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);

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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