I have a large array of boolean values that I'd like to store efficiently in a binary file. The way I have been doing this is to arrange them in groups of 8 booleans (eg T,F,F,T,T,F,T,T), make them into a a string of ones and zeros (eg 10011011), then convert that to a decimal value (eg 155), then pack that into a byte. I repeat this process until I've converted all the boolean values to bytes.

The code I have looks something like this:

$binarydata=null;
$numbooleans=count($array_of_booleans);
for($i=0;$i<ceil($numbooleans/8);$i  ){
        $digits="";
        for($j=0;$j<8;$j  ){
            $counter=$i*8 $j;
            if($counter>=$numbooleans){
                $digits.="0";
            }else{
                if($array_of_booleans[$counter]){
                    $digits.="1";
                }else{
                    $digits.="0";
                }           
            }
        }
        $binarydata.=pack("C",bindec($digits)); 
}

I feel like this method is not efficient. Issues include:

• starting with boolean values, then changing them into the zeros and ones as text. This seems unnecessary
• eight lots of zeros and ones are temporarily stored as a string with 8 characters, is there a way to bypass this step?
• the string with 8 characters is then they are implicitly cast to a binary number in the bindec() function.
• my loop structure to join the values into groups of eight boolean values feels cumbersome

Ideally I'd like to construct the bytes in $binarydata as efficiently as possible. My $array_of_booleans contains tens of millions of values, so efficiency in this algorithm is important.

Can anyone suggest an alternate, more efficient method of converting $array_of_booleans to the $binarydata variable?