PHP Classes

PHP Bit String: Manipulate strings of sequences of binary digits

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This class can manipulate strings of sequences of binary digits.

It can take a string of data or binary digits and create an internal array of data.

The class can convert the bits to hexadecimal, to binary data, or a string of binary digits.

It also provide an iterator interface so it can be treated as an array of bits using the regular array manipulation functions.

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        This example demonstrates the use of the BitString and BitStringIterator classes on a
        simple example string, "ABCDEF", which will be considered as a string of bits.


require_once ( 'BitString.phpclass' ) ;

    if (
php_sapi_name ( ) != 'cli' )
'<pre>' ;

// getbits -
    // This function simply outputs bits from the specified value, up to $count.
function getbits ( $value, $count )
$result = '' ;

        for (
$i = 0 ; $i < $count ; $i ++, $value >>= 1 )
$result .= ( $value & 1 ) ? '1' : '0' ;

        return (
$result ) ;

// Our example string
$data = "ABCDEF" ;

// Create a bit string from it
$bs = new BitString ( $data ) ;

// Try the ToHex() and ToBin() functions. Note that ToBin (0) will print the bits in exactly the same order
    // as they are stored (least significant bit first), while ToBin(1) will print them in the order they are
    // printed by ToHex()
echo "ToHex() : " ; print_r ( $bs -> ToHex ( ) ) ; echo "\n" ;
"ToBin(1) : " ; print_r ( $bs -> ToBin ( 1 ) ) ; echo "\n" ;
"ToBin(0) : " ; print_r ( $bs -> ToBin ( 0 ) ) ; echo "\n" ;

// Use the ArrayAccess interface to retrieve and display each individual bit
echo "Bit per bit (for) : " ;

    for (
$i = 0 ; $i < count ( $bs ) ; $i ++ )
$bs [$i] ;

// Use the Iterator interface to display each individual bit
echo "\nBit per bit (foreach) : " ;

    foreach (
$bs as $bit )
$bit ;

// Now, use the BitString::GetBits() function to display bits by group of x bits, from 1 to 32.
    // Note that the getbits() function defined here will add trailing zeroes for bit counts that are
    // not a denominator of the machine's word size - this is not a bug, this inconvenience was aimed
    // at making this example simpler
for ( $bit_count = 1 ; $bit_count <= 32 ; $bit_count ++ )
sprintf ( "\nTaking by %2d bits : ", $bit_count ) ;
        for (
$i = 0 ; $i < count ( $bs ) ; $i += $bit_count )
$value = $bs -> GetBits ( $i, $bit_count ) ;

            if (
$value === false )
output ( "FALSE for offset $i, count $bit_count" ) ;

getbits ( $value, $bit_count ) ;

// Now use a BitStringIterator object : extract bits from the bit string by groups of
    // 3 components having 8 bits each. It should display the hexadecimal translation of
    // "ABCDEF" which is : "414243444546"
echo "\nBitStringIterator(8,3) : " ;

    foreach ( new
BitStringIterator ( $bs, 8, 3 ) as $values )
        foreach (
$values as $value )
            echo (
sprintf ( "%02X", $value ) ) ;



This package introduces two classes : BitString and BitStringIterator.

A bit string can take as input a string or another bit string. The least significant bit in the string will be the least significant bit of the first byte of the string ; the most significant bit will be the most significant bit of the last byte of the string.

This may seem counter-natural, as we would expect the reverse situation. However, the string is internally converted to an array of little-endian integers (4 bytes on 32 bits systems, 8 bytes on 64-bits ones).

The original intent of this class was to retrieve color values from a stream of bytes ; each color having a number of bits per components, and a number of components per color (for example, 24-bits RGB colors have a number of bits per components of 8, and a number of components per color of 3, one for each of the red, green, blue components).

Anyway, it can be used to retrieve any portion of bits within a bit string using the BitString::GetBits method. The BitStringIterator class has been designed to retrieve things like colors values, but can be used for other purposes.


These classes have been designed with performance in mind ; for this reason, no more than 32 bits can be retrieved at once by the GetBits() method on 32-bits platforms, and no more than 64 on 64-bits platforms. This is not a design issue, but rather a design choice.


In its current state, the BitString class acts as a read-only class : it only extracts bits from a bit string flow.

More features will be added in the future, such as setting bits or performing bitwise operations with other bit strings.


BitString class



$bitstring	=  new BitString ( $data, $data_size_in_bits = false, $filler = 0 ) ;

Creates a bit string based on the supplied string data. The data can be later accessed through one of the following methods :

  • By calling the GetBits() method to retrieve a group of bits
  • By using the array access operator to retrieve an individual bit
  • By using the iterator interface to retrieve individual bits

The parameters are the following :

  • $data (string or BitString) : Data to be used to build the BitString. It can either be : - A string, which will be converted to integer values of size PHP\_INT_\SIZE, in little-endian order. - An existing BitString object, which will be duplicated.
  • $data\_size\_in\_bits (integer) : If not specified, the total number of bits will be the length of $data 8. If specified, indicates the exact number of bits to consider ;$datawill be truncated if this parameter is shorter thatstrlen($data)*, and expanded with the filler value if greater.
  • $filler (byte) : Filler value, for unset bits, specified as a byte. This value is used when the total number of bits does not fit on a byte boundary, or when $data needs to be expanded because $data\_size\_in\_bits is greater than strlen($data) 8. A value offalse,null* or empty string will be interpreted as 0x00.


public function  GetBits ( $offset, $bit_count )

Returns $bit\_count bits starting at the specified offset in the BitString.



The count() function, when applied to a BitString object, will return the actual number of bits.


Allows to access a BitString object as an array, and retrieve each bit. The following example prints out all the bits in a BitString :

$bs 	=  new BiString ( "ABCDEF" ) ;

for  ( $i = 0 ; $i  <  count ( $bs ) ; $i ++ )
	echo $bs [$i] ;


Allows to loop through each bit of a BiString object using a foreach() construct. The following example prints out all the bits in a BitString :

$bs 	=  new BiString ( "ABCDEF" ) ;

foreach  ( $bs  as  $bit )
	echo $bit ;

BitStringIterator class

Allows to iterate through a BitString object and retrieve groups of bits as array.

This class was originally implemented to read a stream of values representing colors, with a specific number of bits per color component, and a number of components per color, but it can be used for many other purposes.


$iterator	=  new BitStringIterator ( $data, $bits_per_component, $component_count = 1 ) ;

The BitStringIterator class allows to iterate through a BitString by groups of $bits\_per\_component bits.

An array of $component\_count elements will be returned upon each iteration.

The parameters are the following :

  • $data (string or BitString) : BitString to be iterated. If a simple string is specified, it will be internally converted to a BitString object.
  • $bits\_per\_component (integer) : Number of bits per component.

$component\_count (integer) : Number of components having $bits\_per\_component bits to be returned upon each iteration.

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