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Diffstat (limited to 'include/utf8/utils/position.php')
| -rw-r--r-- | include/utf8/utils/position.php | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/include/utf8/utils/position.php b/include/utf8/utils/position.php new file mode 100644 index 0000000..7c62d10 --- /dev/null +++ b/include/utf8/utils/position.php @@ -0,0 +1,171 @@ +<?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; +} |