function _transliteration_process

Transliterates UTF-8 encoded text to US-ASCII.

Based on Mediawiki's UtfNormal::quickIsNFCVerify().

Parameters

$string: UTF-8 encoded text input.

$unknown: Replacement string for characters that do not have a suitable ASCII equivalent.

$source_langcode: Optional ISO 639 language code that denotes the language of the input and is used to apply language-specific variations. If the source language is not known at the time of transliteration, it is recommended to set this argument to the site default language to produce consistent results. Otherwise the current display language will be used.

Return value

Transliterated text.:

File

core/includes/transliteration.inc, line 26

Transliteration processing functions.

Code

function _transliteration_process($string, $unknown = '?', $source_langcode = NULL) {
  // ASCII is always valid NFC! If we're only ever given plain ASCII, we can
  // avoid the overhead of initializing the decomposition tables by skipping
  // out early.
  if (!preg_match('/[\x80-\xff]/', $string)) {
    return $string;
  }

  static $tail_bytes;

  if (!isset($tail_bytes)) {
    // Each UTF-8 head byte is followed by a certain number of tail bytes.
    $tail_bytes = array();
    for ($n = 0; $n < 256; $n++) {
      if ($n < 0xc0) {
        $remaining = 0;
      }
      elseif ($n < 0xe0) {
        $remaining = 1;
      }
      elseif ($n < 0xf0) {
        $remaining = 2;
      }
      elseif ($n < 0xf8) {
        $remaining = 3;
      }
      elseif ($n < 0xfc) {
        $remaining = 4;
      }
      elseif ($n < 0xfe) {
        $remaining = 5;
      }
      else {
        $remaining = 0;
      }
      $tail_bytes[chr($n)] = $remaining;
    }
  }

  // Chop the text into pure-ASCII and non-ASCII areas; large ASCII parts can
  // be handled much more quickly. Don't chop up Unicode areas for punctuation,
  // though, that wastes energy.
  preg_match_all('/[\x00-\x7f]+|[\x80-\xff][\x00-\x40\x5b-\x5f\x7b-\xff]*/', $string, $matches);

  $result = '';
  foreach ($matches[0] as $str) {
    if ($str[0] < "\x80") {
      // ASCII chunk: guaranteed to be valid UTF-8 and in normal form C, so
      // skip over it.
      $result .= $str;
      continue;
    }

    // We'll have to examine the chunk byte by byte to ensure that it consists
    // of valid UTF-8 sequences, and to see if any of them might not be
    // normalized.
    //
    // Since PHP is not the fastest language on earth, some of this code is a
    // little ugly with inner loop optimizations.

    $head = '';
    $chunk = strlen($str);
    // Counting down is faster. I'm *so* sorry.
    $len = $chunk + 1;

    for ($i = -1; --$len; ) {
      $c = $str[++$i];
      if ($remaining = $tail_bytes[$c]) {
        // UTF-8 head byte!
        $sequence = $head = $c;
        do {
          // Look for the defined number of tail bytes...
          if (--$len && ($c = $str[++$i]) >= "\x80" && $c < "\xc0") {
            // Legal tail bytes are nice.
            $sequence .= $c;
          }
          else {
            if ($len == 0) {
              // Premature end of string! Drop a replacement character into
              // output to represent the invalid UTF-8 sequence.
              $result .= $unknown;
              break 2;
            }
            else {
              // Illegal tail byte; abandon the sequence.
              $result .= $unknown;
              // Back up and reprocess this byte; it may itself be a legal
              // ASCII or UTF-8 sequence head.
              --$i;
              ++$len;
              continue 2;
            }
          }
        } while (--$remaining);

        $n = ord($head);
        $ord = NULL;
        if ($n <= 0xdf) {
          $ord = ($n - 192) * 64 + (ord($sequence[1]) - 128);
        }
        elseif ($n <= 0xef) {
          $ord = ($n - 224) * 4096 + (ord($sequence[1]) - 128) * 64 + (ord($sequence[2]) - 128);
        }
        elseif ($n <= 0xf7) {
          $ord = ($n - 240) * 262144 + (ord($sequence[1]) - 128) * 4096 + (ord($sequence[2]) - 128) * 64 + (ord($sequence[3]) - 128);
        }
        elseif ($n <= 0xfb) {
          $ord = ($n - 248) * 16777216 + (ord($sequence[1]) - 128) * 262144 + (ord($sequence[2]) - 128) * 4096 + (ord($sequence[3]) - 128) * 64 + (ord($sequence[4]) - 128);
        }
        elseif ($n <= 0xfd) {
          $ord = ($n - 252) * 1073741824 + (ord($sequence[1]) - 128) * 16777216 + (ord($sequence[2]) - 128) * 262144 + (ord($sequence[3]) - 128) * 4096 + (ord($sequence[4]) - 128) * 64 + (ord($sequence[5]) - 128);
        }
        $result .= _transliteration_replace($ord, $unknown, $source_langcode);
        $head = '';
      }
      elseif ($c < "\x80") {
        // ASCII byte.
        $result .= $c;
        $head = '';
      }
      elseif ($c < "\xc0") {
        // Illegal tail bytes.
        if ($head == '') {
          $result .= $unknown;
        }
      }
      else {
        // Miscellaneous freaks.
        $result .= $unknown;
        $head = '';
      }
    }
  }
  return $result;
}