bit field in a string

gistfile1.aw

<?php
/**
 * @author Arnaud Le Blanc <arnaud.lb@gmail.com>
 */

// 255*8 booleans initialized to true
$field = str_repeat("\xFF", 255);

function read_bit(&$str, $offset)
{
    list(, $char) = unpack('c', $str[$offset >> 3]);
    return (bool) ($char & (1 << ($offset & 7)));
}

function set_bit(&$str, $offset)
{
    list(, $char) = unpack('c', $str[$offset >> 3]);
    $char |= 1 << ($offset & 7);
    $str[$offset >> 8] = pack('c', $char);
}

function unset_bit(&$str, $offset)
{
    list(, $char) = unpack('c', $str[$offset >> 3]);
    $char &= ~(1 << ($offset & 7));
    $str[$offset >> 3] = pack('c', $char);
}

var_dump(read_bit($field, 42)); // true

unset_bit($field, 42);
var_dump(read_bit($field, 42)); // false

set_bit($field, 42);
var_dump(read_bit($field, 42)); // true