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### Answer: How do I convert a very long bit string into a number?

by jdporter (Canon)
 on Jan 15, 2009 at 21:46 UTC Need Help??

Q&A > math > How do I convert a very long bit string into a number? - Answer contributed by jdporter

Combine unpack with Math::BigInt:
```use Math::BigInt;
use bigint;
use strict;
use warnings;

sub convert_bitstring_to_number
{
my \$bitstring = shift;
my \$h = unpack( 'H*', \$bitstring );
my \$bh = new Math::BigInt '0x'.\$h;
\$bh->as_int;
}

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Re: Answer: How do I convert a very long bit string into a number?
by gone2015 (Deacon) on Jan 16, 2009 at 02:00 UTC

This can be generalised for other orderings of the bytes, and of the bits in each byte, of the bitstring. Four types of bitstring can be identified:

1. big-endian: ms-bit of first byte is the ms-bit of the multi-byte number. This is handled as shown, ie:

```  my \$h = unpack( 'H*', \$bitstring ) ;

2. little-endian: ls-bit of first byte is the ls-bit of the multi-byte number. This is handled:

```  my \$h = unpack( 'H*', scalar reverse \$bitstring ) ;
Note that this is the same order as vec(\$v, \$b, 1)

3. big-endian reversed bytes: ls-bit of first byte is the ms-bit of the multi-byte number. This is handled:

```  my \$h = unpack( 'H*', pack('b*', unpack('B*', \$bitstring)) ) ;

4. little-endian reversed bytes: ms-bit of first byte is the ls-bit of the multi-byte number. This is handled:

```  my \$h = unpack( 'H*', pack('b*', unpack('B*', scalar reverse \$bitstr
+ing)) ) ;

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