php 字符串、文件转化成二进制流文件

$file1 = 'F:/46.gif';
$file2 = 'F:/test.txt';
$file3 = 'F:/47.gif';
$size = filesize($file1);
echo '文件大小为：'.$size;
echo "\n<br>转化为二进制 ...";
$content = file_get_contents($file1);
$content = bstr2bin($content);
$fp = fopen($file2, 'w');
fwrite($fp, $content);
fclose($fp);
$size2 = filesize($file2);
echo '转化成二进制后文件大小为：'.$size2;
$content = bin2bstr($content);
$fp = fopen($file3, 'w');
fwrite($fp, $content);
fclose($fp);
function bin2bstr($input)
// Convert a binary expression (e.g., "100111") into a binary-string
{
  if (!is_string($input)) return null; // Sanity check
  // Pack into a string
  $input = str_split($input, 4);
  $str = '';
  foreach ($input as $v)
  {
   $str .= base_convert($v, 2, 16);
  }
 
  $str =  pack('H*', $str);
 
  return $str;
}
function bstr2bin($input)
// Binary representation of a binary-string
{
  if (!is_string($input)) return null; // Sanity check
  // Unpack as a hexadecimal string
  $value = unpack('H*', $input);
 
  // Output binary representation
  $value = str_split($value[1], 1);
  $bin = '';
  foreach ($value as $v)
  {
   $b = str_pad(base_convert($v, 16, 2), 4, '0', STR_PAD_LEFT);
   
   $bin .= $b;
  }
 
  return $bin;
}