file_scan_directory.php

<?php

function file_scan_directory($dir, $mask, $options = array(), $depth = 0) {

  [..]

  if ($options['nomask'] === NULL
    && $options['recurse']
    // Detect patterns like '/\.tpl\.php$/' or '/[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*\.module$/'.
    // The first part is
    && preg_match('@/(.*?[^\\\\]|)((?:[_a-zA-Z0-9]|\\\\\\.)*)\$/@', $mask, $m)
  ) {
    // Use a faster algorithm for this special case.
    list(, $basename_pattern, $extension_pattern) = $m;
    $basename_pattern = ('' !== $basename_pattern)
      ? '/' . $basename_pattern . '$/'
      : NULL;
    $extension = str_replace('\\.' , '.', $extension_pattern);
    return _drupal_file_scan_directory_fast($dir, $basename_pattern, $extension, $options);
  }