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Also simplified some parts of the algorithm implementation Part of this simplification involves the use of goto statementsmaster
2 changed files with 220 additions and 87 deletions
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<?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 JKingWeb\URI; |
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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 = ($pos < strlen($string)) ? $string[$pos] : ""; |
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if ($b < "\x80" || $b=="") { |
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// if the byte is an ASCII character or end of input, simply return it |
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$next = $pos + 1; |
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return $b; |
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} else { |
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$errMode = $errMode ?? self::$errMode; |
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// otherwise determine the byte-length of the UTF-8 character |
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$l = self::l($b); |
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if (!$l && $errMode==self::M_SKIP) { |
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// if the byte is invalid and we're supposed to skip, advance the position and start over |
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$pos++; |
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goto start; |
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} elseif (!$l && $errMode == self::M_REPLACE) { |
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// if the byte is invalid and we're supposed to replace, return a replacement character |
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$next = $pos + 1; |
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return self::$replacementChar; |
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} elseif (!$l) { |
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// if the byte is invalid and we're supposed to halt, halt |
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throw new \Exception; |
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} else { |
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// otherwise collect valid mid-sequence bytes into a buffer until the whole character is retrieved or an invalid byte is encountered |
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$buffer = $b; |
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do { |
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$b = (++$pos < strlen($string)) ? $string[$pos] : ""; |
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if ($b >= "\x80" && $b <= "\xBF") { |
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// if the byte is valid, add it to the buffer |
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$buffer .= $b; |
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} elseif ($errMode==self::M_SKIP) { |
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// if the byte is invalid and we're supposed to skip, start over from the current position |
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goto start; |
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} elseif ($errMode==self::M_REPLACE) { |
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// if the byte is invalid and we're supposed to replace, return a replacement character |
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$next = $pos; |
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return self::$replacementChar; |
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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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} while (strlen($buffer) < $l); |
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// return the filled buffer and the position of the next byte |
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$next = $pos + 1; |
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return $buffer; |
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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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$b = ($pos < strlen($string)) ? $string[$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 // stop once the start of the string has been reached |
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); |
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// get the expected length of the character starting at the last examined byte |
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$l = self::l($b); |
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if ($l==$t) { |
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// if the expected length matches the number of examined bytes, the character is valid |
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return $pos; |
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} elseif ($errMode==self::M_SKIP) { |
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// if we're expected to ignore invalid sequences: |
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if ($l && $t > $l) { |
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// if the last examined byte is the start of a sequence and we have more than the right amount of continuation characters, return the current position |
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return $pos; |
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} elseif (!$pos) { |
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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 ($errMode==self::M_REPLACE) { |
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// if we're expected to treat invalid sequences as replacement characters, return |
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// the offset of the most recently examined byte if it is the start of a multi-byte |
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// sequence, or the starting offset otherwise: in the latter case the original byte |
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// is itself a replacement character position |
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return ($l > 1) ? $pos: $s; |
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} else { |
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// 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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/** |
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* Returns the expected byte length of a UTF-8 character starting with byte $b |
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* |
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* If the byte is not the start of a UTF-8 sequence, 0 is returned |
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*/ |
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protected static function l(string $b): int { |
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if ($b >= "\xC0" && $b <= "\xDF") { // two-byte character |
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return 2; |
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} elseif ($b >= "\xE0" && $b <= "\xEF") { // three-byte character |
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return 3; |
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} elseif ($b >= "\xF0" && $b <= "\xF7") { // four-byte character |
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return 4; |
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} elseif ($b < "\x80") { // ASCII byte: one-byte character |
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return 1; |
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} elseif ($b == "") { // end of input: pretend it's a valid single-byte character |
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return 1; |
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} else { // invalid byte |
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return 0; |
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} |
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} |
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} |
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