Experiment: Add optimized set lookup class

Author: dmsnell

src/wp-includes/class-wp-token-set.php

@@ -0,0 +1,224 @@
+<?php
+
+class WP_Token_Set {
+	const MAX_LENGTH = 256;
+
+	private $key_length = 2;
+
+	/**
+	 * Stores an optimized form of the word set, where words are grouped
+	 * by first two letters and then collapsed into a string.
+	 *
+	 * @var array
+	 */
+	private $large_words = array();
+
+	/**
+	 * Stores an optimized row of short words, where every entry is two
+	 * bytes long and zero-extended if the word is only a single byte.
+	 *
+	 * @var string
+	 */
+	private $small_words = '';
+
+	public static function from_array( $words, $key_length = 2 ) {
+		$set             = new WP_Token_Set();
+		$set->key_length = $key_length;
+
+		// Start by grouping words.
+
+		$groups = array();
+		$shorts = array();
+		foreach ( $words as $word ) {
+			if ( ! is_string( $word ) || self::MAX_LENGTH <= strlen( $word ) ) {
+				return null;
+			}
+
+			$length = strlen( $word );
+
+			if ( $key_length >= $length ) {
+				$shorts[] = $word;
+			} else {
+				$group = substr( $word, 0, $key_length );
+
+				if ( ! isset( $groups[ $group ] ) ) {
+					$groups[ $group ] = array();
+				}
+
+				$groups[ $group ][] = substr( $word, $key_length );
+			}
+		}
+
+		// Sort the words by longest-first, then alphabetical.
+
+		usort( $shorts, array( self::class, 'longest_first_then_alphabetical' ) );
+		foreach ( $groups as $group_key => $group ) {
+			usort( $groups[ $group_key ], array( self::class, 'longest_first_then_alphabetical' ) );
+		}
+
+		// Finally construct the optimized lookups.
+
+		foreach ( $shorts as $word ) {
+			$set->small_words .= str_pad( $word, $key_length, "\x00" );
+		}
+
+		foreach ( $groups as $group => $group_words ) {
+			$group_string = '';
+
+			foreach ( $group_words as $word ) {
+				$group_string .= chr( strlen( $word ) ) . $word;
+			}
+
+			$set->large_words[ $group ] = $group_string;
+		}
+
+		return $set;
+	}
+
+	public static function from_precomputed_table( $key_length, $large_words, $small_words ) {
+		$set = new WP_Token_Set();
+
+		$set->key_length  = $key_length;
+		$set->large_words = $large_words;
+		$set->small_words = $small_words;
+
+		return $set;
+	}
+
+	public function contains( $word ) {
+		if ( $this->key_length >= strlen( $word ) ) {
+			return str_contains( $this->small_words, str_pad( $word, $this->key_length, "\x00" ) );
+		}
+
+		$group_key = substr( $word, 0, $this->key_length );
+		if ( ! isset( $this->large_words[ $group_key ] ) ) {
+			return false;
+		}
+
+		$group  = $this->large_words[ $group_key ];
+		$slug   = substr( $word, $this->key_length );
+		$length = strlen( $slug );
+		$at     = 0;
+		while ( $at < strlen( $group ) ) {
+			$token_length = ord( $group[ $at++ ] );
+			if ( $token_length === $length && 0 === substr_compare( $group, $slug, $at, $token_length ) ) {
+				return true;
+			}
+
+			$at += $token_length;
+		}
+
+		return false;
+	}
+
+	public function read_token( $text, $offset ) {
+		$text_length = strlen( $text );
+
+		// Search for a long word first, if the text is long enough, and if that fails, a short one.
+		if ( $this->key_length < $text_length ) {
+			$group_key = substr( $text, $offset, $this->key_length );
+
+			if ( ! isset( $this->large_words[ $group_key ] ) ) {
+				return false;
+			}
+
+			$group        = $this->large_words[ $group_key ];
+			$group_length = strlen( $group );
+			$at           = 0;
+			while ( $at < $group_length ) {
+				$token_length = ord( $group[ $at++ ] );
+				$token        = substr( $group, $at, $token_length );
+
+				if ( 0 === substr_compare( $text, $token, $offset + $this->key_length, $token_length ) ) {
+					return $group_key . $token;
+				}
+
+				$at += $token_length;
+			}
+		}
+
+		// Perhaps a short word then.
+		$small_text = str_pad( substr( $text, $offset, $this->key_length ), $this->key_length, "\x00" );
+		$at         = strpos( $this->small_words, $small_text );
+
+		return false !== $at
+			? rtrim( substr( $this->small_words, $at, $this->key_length ), "\x00" )
+			: false;
+	}
+
+	public function to_array() {
+		$tokens = array();
+
+		$at = 0;
+		while ( $at < strlen( $this->small_words ) ) {
+			$tokens[] = rtrim( substr( $this->small_words, $at, $this->key_length ), "\x00" );
+			$at      += $this->key_length;
+		}
+
+		foreach ( $this->large_words as $prefix => $group ) {
+			$at = 0;
+			while ( $at < strlen( $group ) ) {
+				$length   = ord( $group[ $at++ ] );
+				$tokens[] = $prefix . rtrim( substr( $group, $at, $length ), "\x00" );
+				$at      += $length;
+			}
+		}
+
+		return $tokens;
+	}
+
+	public function precomputed_php_source_table( $indent = "\t" ) {
+		$i1 = $indent;
+		$i2 = $indent . $indent;
+
+		$output  = self::class . "::from_precomputed_table(\n";
+		$output .= "{$i1}{$this->key_length},\n";
+		$output .= "{$i1}array(\n";
+
+		$prefixes = array_keys( $this->large_words );
+		sort( $prefixes );
+		foreach ( $prefixes as $prefix ) {
+			$group        = $this->large_words[ $prefix ];
+			$comment_line = "{$i2}//";
+			$data_line    = "{$i2}'{$prefix}' => \"";
+			$at           = 0;
+			while ( $at < strlen( $group ) ) {
+				$length = ord( $group[ $at++ ] );
+				$digits = str_pad( dechex( $length ), 2, '0', STR_PAD_LEFT );
+				$token  = substr( $group, $at, $length );
+				$at    += $length;
+
+				$comment_line .= " &{$prefix}{$token}";
+				$data_line    .= "\\x{$digits}{$token}";
+			}
+			$comment_line .= "\n";
+			$data_line    .= "\",\n";
+
+			$output .= $comment_line;
+			$output .= $data_line;
+		}
+
+		$output    .= "{$i1}),\n";
+		$small_text = str_replace( "\x00", '\x00', $this->small_words );
+		$output    .= "{$i1}'{$small_text}'\n";
+		$output    .= ");\n";
+
+		return $output;
+	}
+
+	private static function longest_first_then_alphabetical( $a, $b ) {
+		if ( $a === $b ) {
+			return 0;
+		}
+
+		$la = strlen( $a );
+		$lb = strlen( $b );
+
+		// Longer strings are less-than for comparison's sake.
+		if ( $la !== $lb ) {
+			return $lb - $la;
+		}
+
+		return strcmp( $a, $b );
+	}
+}