source: trunk/web/punbb/include/utf8/utils/position.php

<?php

/**
* Locate a byte index given a UTF-8 character index
* @version $Id: position.php,v 1.1 2006/10/01 00:01:31 harryf Exp $
* @package utf8
* @subpackage position
*/

/**
* Given a string and a character index in the string, in
* terms of the UTF-8 character position, returns the byte
* index of that character. Can be useful when you want to
* PHP's native string functions but we warned, locating
* the byte can be expensive
* Takes variable number of parameters - first must be
* the search string then 1 to n UTF-8 character positions
* to obtain byte indexes for - it is more efficient to search
* the string for multiple characters at once, than make
* repeated calls to this function
*
* @author Chris Smith<chris@jalakai.co.uk>
* @param string string to locate index in
* @param int (n times)
* @return mixed - int if only one input int, array if more
* @return boolean TRUE if it's all ASCII
* @package utf8
* @subpackage position
*/
function utf8_byte_position()
{
        $args = func_get_args();
        $str =& array_shift($args);

        if (!is_string($str))
                return false;

        $result = array();
        $prev = array(0, 0); // Trivial byte index, character offset pair
        $i = utf8_locate_next_chr($str, 300); // Use a short piece of str to estimate bytes per character. $i (& $j) -> byte indexes into $str
        $c = strlen(utf8_decode(substr($str, 0, $i))); // $c -> character offset into $str

        // Deal with arguments from lowest to highest
        sort($args);

        foreach ($args as $offset)
        {
                // Sanity checks FIXME

                // 0 is an easy check
                if ($offset == 0)
                {
                        $result[] = 0; continue;
                }

                // Ensure no endless looping
                $safety_valve = 50;

                do
                {
                        if (($c - $prev[1]) == 0)
                        {
                                // Hack: gone past end of string
                                $error = 0;
                                $i = strlen($str);
                                break;
                        }

                        $j = $i + (int)(($offset-$c) * ($i - $prev[0]) / ($c - $prev[1]));
                        $j = utf8_locate_next_chr($str, $j); // Correct to utf8 character boundary
                        $prev = array($i,$c); // Save the index, offset for use next iteration

                        if ($j > $i)
                                $c += strlen(utf8_decode(substr($str, $i, $j-$i))); // Determine new character offset
                        else
                                $c -= strlen(utf8_decode(substr($str, $j, $i-$j))); // Ditto

                        $error = abs($c-$offset);
                        $i = $j; // Ready for next time around
                }
                while (($error > 7) && --$safety_valve); // From 7 it is faster to iterate over the string

                if ($error && $error <= 7)
                {
                        if ($c < $offset)
                        {
                                // Move up
                                while ($error--)
                                        $i = utf8_locate_next_chr($str, ++$i);
                        }
                        else
                        {
                                // Move down
                                while ($error--)
                                        $i = utf8_locate_current_chr($str, --$i);
                        }

                        // Ready for next arg
                        $c = $offset;
                }

                $result[] = $i;
        }

        if (count($result) == 1)
                return $result[0];

        return $result;
}

/**
* Given a string and any byte index, returns the byte index
* of the start of the current UTF-8 character, relative to supplied
* position. If the current character begins at the same place as the
* supplied byte index, that byte index will be returned. Otherwise
* this function will step backwards, looking for the index where
* curent UTF-8 character begins
* @author Chris Smith<chris@jalakai.co.uk>
* @param string
* @param int byte index in the string
* @return int byte index of start of next UTF-8 character
* @package utf8
* @subpackage position
*/
function utf8_locate_current_chr( &$str, $idx )
{
        if ($idx <= 0)
                return 0;

        $limit = strlen($str);
        if ($idx >= $limit)
                return $limit;

        // Binary value for any byte after the first in a multi-byte UTF-8 character
        // will be like 10xxxxxx so & 0xC0 can be used to detect this kind
        // of byte - assuming well formed UTF-8
        while ($idx && ((ord($str[$idx]) & 0xC0) == 0x80))
                $idx--;

        return $idx;
}

/**
* Given a string and any byte index, returns the byte index
* of the start of the next UTF-8 character, relative to supplied
* position. If the next character begins at the same place as the
* supplied byte index, that byte index will be returned.
* @author Chris Smith<chris@jalakai.co.uk>
* @param string
* @param int byte index in the string
* @return int byte index of start of next UTF-8 character
* @package utf8
* @subpackage position
*/
function utf8_locate_next_chr(&$str, $idx)
{
        if ($idx <= 0)
                return 0;

        $limit = strlen($str);
        if ($idx >= $limit)
                return $limit;

        // Binary value for any byte after the first in a multi-byte UTF-8 character
        // will be like 10xxxxxx so & 0xC0 can be used to detect this kind
        // of byte - assuming well formed UTF-8
        while (($idx < $limit) && ((ord($str[$idx]) & 0xC0) == 0x80))
                $idx++;

        return $idx;
}