How to output an 8 charactor bit representation string as a single byte to a file?

Question

I got a file with 2880 characters having ONLY 1s and 0s.

Each of the characters occupy one byte in the file.

We want to move chunks of 8 characters, treat it as a bit representation and move it as one byte into a new file. The result is then a file with the size of 1/8th of the original file.

So far I got:

$filename = "/var/www/BB/file.ppm2"; 
$handle = fopen($filename, "rb"); 
$fsize = filesize($filename); 
$content_read = substr(fread($handle, $fsize), 0, 8640);    

for($i = 0; $i <360; $i++) {
    $offset_8 = $i * 8;
    $content_read_8 = substr($content_read, $offset_8, 8);

But how can I get the content of $content_read_8 (ex. 01101101) into a one character byte: $byte_out ???

Thanks for you help ;-)

Answer 1

Does this do what you're looking for?

<?php
$output = "";
$filename = "/var/www/BB/file.ppm2";
$content = file_get_contents($filename);
$content = str_split($content, 8);
foreach($content as $char) {
    $output .= chr(bindec($char));
}
?>

Answer 2

You can use bitwise operations:

for($i = 0; $i <360; $i++) {
  $offset_8 = $i * 8;
  $content_read_8 = substr($content_read, $offset_8, 8);

  $char = 0;
  for ($j = 0; $j < 8; $j += 1) {
    // Move all the bits 1 place to the left - its like sticking a 0 to the right.
    $char << 1;
    // If its a '1' char, you need to adjust that bit
    if ($content_read_8[$j] == '1') {
      $char += 1;
    }
  }
}

You can read more on PHP bitwise operators here