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284 lines
12 KiB
284 lines
12 KiB
<?php
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/** @license MIT
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* Copyright 2018 J. King et al.
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* See LICENSE and AUTHORS files for details */
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declare(strict_types=1);
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namespace MensBeam\UTF8;
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abstract class UTF8 {
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public static $replacementChar = "\u{FFFD}";
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public static $errMode = self::M_REPLACE;
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const M_REPLACE = 0;
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const M_SKIP = 1;
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const M_HALT = 2;
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/** Retrieve a character from $string starting at byte offset $pos
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*
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* $next is a variable in which to store the next byte offset at which a character starts
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*
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* The returned character may be a replacement character, or the empty string if $pos is beyond the end of $string
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*/
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public static function get(string $string, int $pos, &$next = null, int $errMode = null): string {
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start:
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// get the byte at the specified position
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$b = @$string[$pos];
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if (ord($b) < 0x80) {
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// if the byte is an ASCII character or end of input, simply return it
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$next = $pos + 1;
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return $b;
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} else {
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// otherwise determine the numeric code point of the character, as well as the position of the next character
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$p = self::ord($string, $pos, $next, self::M_REPLACE);
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if (is_int($p)) {
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// if the character is valid, return its serialization
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// we do a round trip (bytes > code point > bytes) to normalize overlong sequences
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return self::chr($p);
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} else {
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$errMode = $errMode ?? self::$errMode;
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if ($errMode==self::M_REPLACE) {
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// if the byte is invalid and we're supposed to replace, return a replacement character
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return self::$replacementChar;
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} elseif ($errMode==self::M_SKIP) {
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// if the character is invalid and we're supposed to skip invalid characters, advance the position and start over
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$pos = $next;
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goto start;
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} else {
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// if the byte is invalid and we're supposed to halt, halt
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throw new \Exception;
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}
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}
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}
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}
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/** Starting from byte offset $pos, advance $num characters through $string and return the byte offset of the found character
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*
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* If $num is negative, the operation will be performed in reverse
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*
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* If $pos is omitted, the start of the string will be used for a forward seek, and the end for a reverse seek
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*/
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public static function seek(string $string, int $num, int $pos = null, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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if ($num > 0) {
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$pos = $pos ?? 0;
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do {
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$c = self::get($string, $pos, $pos, $errMode); // the current position is getting overwritten with the next position, by reference
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} while (--$num && $c != ""); // stop after we have skipped the desired number of characters, or reached EOF
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return $pos;
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} elseif ($num < 0) {
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$pos = $pos ?? strlen($string);
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if (!$pos) {
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// if we're already at the start of the string, we can't go further back
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return $pos;
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}
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$num = abs($num);
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do {
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$pos = self::sync($string, $pos -1, $errMode);
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$num--;
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} while ($num && $pos);
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return $pos;
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} else {
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// seeking zero characters is equivalent to a sync
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return self::sync($string, $pos, $errMode);
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}
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}
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/** Synchronize to the byte offset of the start of the nearest character at or before byte offset $pos */
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public static function sync(string $string, int $pos, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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start:
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if (!$pos || $pos >= strlen($string)) {
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// if we're at the start of the string or past its end, then this is the character start
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return $pos;
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}
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// save the start position for later, and increment before the coming decrement loop
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$s = $pos++;
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// examine the current byte and skip up to three continuation bytes, going backward and counting the number of examined bytes (between 1 and 4)
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$t = 0;
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do {
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$pos--;
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$t++;
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$b = @$string[$pos];
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} while (
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$b >= "\x80" && $b <= "\xBF" && // continuation bytes
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($t < 4 || $errMode==self::M_SKIP) && // stop after four bytes, unless we're skipping invalid sequences
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$pos > 0 // stop once the start of the string has been reached
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);
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// attempt to extract a code point at the current position
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$p = self::ord($string, $pos, $n, self::M_REPLACE);
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// if the position of the character after the one we just consumed is earlier than our start position,
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// then there was at least one invalid sequence between the consumed character and the start position
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if ($n < $s) {
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if ($errMode==self::M_SKIP) {
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// if we're supposed to skip invalid sequences, there is no need to do anything
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} elseif ($errMode==self::M_REPLACE) {
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// if we're supposed to replace invalid sequences, return the starting offset: it is itself a character
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return $s;
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} else {
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// otherwise if the character is invalid and we're expected to halt, halt
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throw new \Exception;
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}
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}
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// if the consumed character is valid, return the current position
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if (is_int($p)) {
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return $pos;
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} elseif ($errMode==self::M_SKIP) {
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// if we're supposed to skip invalid sequences:
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if ($pos < 1) {
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// if we're already at the start of the string, give up
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return $pos;
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} else {
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// otherwise skip over the last examined byte and start over
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$pos--;
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goto start;
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}
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} elseif ($errMode==self::M_REPLACE) {
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// if we're supposed to replace invalid sequences, return the current offset: we've synchronized
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return $pos;
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} else {
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// otherwise if the character is invalid and we're expected to halt, halt
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throw new \Exception;
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}
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}
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public static function len(string $string, int $start = 0, int $end = null, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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$end = $end ?? strlen($string);
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if (substr($string, $start, ($end - $start)) =="") {
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return 0;
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}
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$count = 0;
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$pos = $start;
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do {
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$c = self::get($string, $pos, $pos, $errMode);
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} while ($c != "" && ++$count && $pos < $end);
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return $count;
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}
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public static function substr(string $str, int $start = 0, int $length = null, &$next = null, int $errMode = null): string {
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$errMode = $errMode ?? self::$errMode;
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if ($length > 0) {
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$pos = $start;
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$buffer = "";
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do {
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$c = self::get($string, $pos, $pos, $errMode); // the current position is getting overwritten with the next position, by reference
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$buffer .= $c;
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} while (--$length && $c != ""); // stop after we have skipped the desired number of characters, or reached EOF
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$next = $pos;
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return $buffer;
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} else {
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$next = self::sync($string, $start, $errMode);
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return "";
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}
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}
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/** Decodes the first UTF-8 character from a byte sequence into a numeric code point, starting at byte offset $pos
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*
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* Upon success, returns the numeric code point of the character, an integer between 0 and 1114111
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*
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* Upon error, returns false; if $char is the empty string or $pos is beyond the end of the string, null is returned
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*
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* $next is a variable in which to store the next byte offset at which a character starts
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*/
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public static function ord(string $string, int $pos = 0, &$next = null, int $errMode = null) {
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// this function effectively implements https://encoding.spec.whatwg.org/#utf-8-decoder
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// though it differs from a slavish implementation because it operates on only a single
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// character rather than a whole stream
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start:
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// optimization for ASCII characters
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$b = @$string[$pos];
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if ($b=="") {
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$next = $pos + 1;
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return null;
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} elseif (($b = ord($b)) < 0x80) {
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$next = $pos + 1;
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return $b;
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}
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$point = 0;
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$seen = 0;
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$needed = 1;
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$lower = 0x80;
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$upper = 0xBF;
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while ($seen < $needed) {
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$b = ord(@$string[$pos++]);
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if (!$seen) {
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if ($b >= 0xC2 && $b <= 0xDF) { // two-byte character
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$needed = 2;
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$point = $b & 0x1F;
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} elseif ($b >= 0xE0 && $b <= 0xEF) { // three-byte character
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$needed = 3;
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if ($b==0xE0) {
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$lower = 0xA0;
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} elseif ($b==0xED) {
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$upper = 0x9F;
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}
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$point = $b & 0xF;
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} elseif ($b >= 0xF0 && $b <= 0xF4) { // four-byte character
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$needed = 4;
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if ($b==0xF0) {
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$lower = 0x90;
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} elseif ($b==0xF4) {
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$upper = 0x8F;
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}
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$point = $b & 0x7;
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} else { // invalid byte
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$next = $pos;
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switch ($errMode ?? self::$errMode) {
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case self::M_SKIP:
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goto start;
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case self::M_REPLACE:
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return false;
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default:
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throw new \Exception;
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}
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}
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} elseif ($b < $lower || $b > $upper) {
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$next = $pos - 1;
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switch ($errMode ?? self::$errMode) {
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case self::M_SKIP:
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goto start;
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case self::M_REPLACE:
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return false;
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default:
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throw new \Exception;
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}
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} else {
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$lower = 0x80;
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$upper = 0xBF;
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$point = ($point << 6) | ($b & 0x3F);
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}
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$seen++;
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}
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$next = $pos;
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return $point;
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}
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/** Returns the UTF-8 encoding of $codePoint
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*
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* If $codePoint is less than 0 or greater than 1114111, an empty string is returned
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*/
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public static function chr(int $codePoint): string {
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// this function implements https://encoding.spec.whatwg.org/#utf-8-encoder
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if ($codePoint < 0 || $codePoint > 0x10FFFF) {
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return "";
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} elseif ($codePoint < 128) {
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return chr($codePoint);
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} elseif ($codePoint < 0x800) {
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$count = 1;
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$offset = 0xC0;
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} elseif ($codePoint < 0x10000) {
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$count = 2;
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$offset = 0xE0;
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} else {
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$count = 3;
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$offset = 0xF0;
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}
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$bytes = chr(($codePoint >> (6 * $count)) + $offset);
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while ($count > 0) {
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$bytes .= chr(0x80 | (($codePoint >> (6 * ($count - 1))) & 0x3F));
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$count--;
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}
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return $bytes;
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}
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}
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