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<?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;
}
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