diff -r c7c34916027a -r 177826044cd9 wp/wp-includes/class-wp-text-diff-renderer-table.php
--- a/wp/wp-includes/class-wp-text-diff-renderer-table.php	Mon Oct 14 18:06:33 2019 +0200
+++ b/wp/wp-includes/class-wp-text-diff-renderer-table.php	Mon Oct 14 18:28:13 2019 +0200
@@ -20,7 +20,7 @@
 	 * @var int
 	 * @since 2.6.0
 	 */
-	public $_leading_context_lines  = 10000;
+	public $_leading_context_lines = 10000;
 
 	/**
 	 * @see Text_Diff_Renderer::_trailing_context_lines
@@ -56,6 +56,22 @@
 	protected $compat_fields = array( '_show_split_view', 'inline_diff_renderer', '_diff_threshold' );
 
 	/**
+	 * Caches the output of count_chars() in compute_string_distance()
+	 *
+	 * @var array
+	 * @since 5.0.0
+	 */
+	protected $count_cache = array();
+
+	/**
+	 * Caches the difference calculation in compute_string_distance()
+	 *
+	 * @var array
+	 * @since 5.0.0
+	 */
+	protected $difference_cache = array();
+
+	/**
 	 * Constructor - Call parent constructor with params array.
 	 *
 	 * This will set class properties based on the key value pairs in the array.
@@ -66,8 +82,9 @@
 	 */
 	public function __construct( $params = array() ) {
 		parent::__construct( $params );
-		if ( isset( $params[ 'show_split_view' ] ) )
-			$this->_show_split_view = $params[ 'show_split_view' ];
+		if ( isset( $params['show_split_view'] ) ) {
+			$this->_show_split_view = $params['show_split_view'];
+		}
 	}
 
 	/**
@@ -86,7 +103,7 @@
 	 * @param array $lines
 	 * @param string $prefix
 	 */
-	public function _lines( $lines, $prefix=' ' ) {
+	public function _lines( $lines, $prefix = ' ' ) {
 	}
 
 	/**
@@ -138,7 +155,7 @@
 	 */
 	public function _added( $lines, $encode = true ) {
 		$r = '';
-		foreach ($lines as $line) {
+		foreach ( $lines as $line ) {
 			if ( $encode ) {
 				$processed_line = htmlspecialchars( $line );
 
@@ -153,7 +170,7 @@
 				 *
 				 * @param String $processed_line The processed diffed line.
 				 * @param String $line           The unprocessed diffed line.
-		 		 * @param string null            The line context. Values are 'added', 'deleted' or 'unchanged'.
+				 * @param string null            The line context. Values are 'added', 'deleted' or 'unchanged'.
 				 */
 				$line = apply_filters( 'process_text_diff_html', $processed_line, $line, 'added' );
 			}
@@ -176,7 +193,7 @@
 	 */
 	public function _deleted( $lines, $encode = true ) {
 		$r = '';
-		foreach ($lines as $line) {
+		foreach ( $lines as $line ) {
 			if ( $encode ) {
 				$processed_line = htmlspecialchars( $line );
 
@@ -188,7 +205,6 @@
 			} else {
 				$r .= '<tr>' . $this->deletedLine( $line ) . "</tr>\n";
 			}
-
 		}
 		return $r;
 	}
@@ -202,15 +218,15 @@
 	 */
 	public function _context( $lines, $encode = true ) {
 		$r = '';
-		foreach ($lines as $line) {
+		foreach ( $lines as $line ) {
 			if ( $encode ) {
 				$processed_line = htmlspecialchars( $line );
 
 				/** This filter is documented in wp-includes/wp-diff.php */
 				$line = apply_filters( 'process_text_diff_html', $processed_line, $line, 'unchanged' );
 			}
-			if (  $this->_show_split_view ) {
-				$r .= '<tr>' . $this->contextLine( $line ) . $this->emptyLine() . $this->contextLine( $line )  . "</tr>\n";
+			if ( $this->_show_split_view ) {
+				$r .= '<tr>' . $this->contextLine( $line ) . $this->emptyLine() . $this->contextLine( $line ) . "</tr>\n";
 			} else {
 				$r .= '<tr>' . $this->contextLine( $line ) . "</tr>\n";
 			}
@@ -248,58 +264,62 @@
 
 		// Compute word diffs for each matched pair using the inline diff
 		foreach ( $orig_matches as $o => $f ) {
-			if ( is_numeric($o) && is_numeric($f) ) {
-				$text_diff = new Text_Diff( 'auto', array( array($orig[$o]), array($final[$f]) ) );
-				$renderer = new $this->inline_diff_renderer;
-				$diff = $renderer->render( $text_diff );
+			if ( is_numeric( $o ) && is_numeric( $f ) ) {
+				$text_diff = new Text_Diff( 'auto', array( array( $orig[ $o ] ), array( $final[ $f ] ) ) );
+				$renderer  = new $this->inline_diff_renderer;
+				$diff      = $renderer->render( $text_diff );
 
 				// If they're too different, don't include any <ins> or <dels>
 				if ( preg_match_all( '!(<ins>.*?</ins>|<del>.*?</del>)!', $diff, $diff_matches ) ) {
 					// length of all text between <ins> or <del>
-					$stripped_matches = strlen(strip_tags( join(' ', $diff_matches[0]) ));
+					$stripped_matches = strlen( strip_tags( join( ' ', $diff_matches[0] ) ) );
 					// since we count lengith of text between <ins> or <del> (instead of picking just one),
 					//	we double the length of chars not in those tags.
-					$stripped_diff = strlen(strip_tags( $diff )) * 2 - $stripped_matches;
-					$diff_ratio = $stripped_matches / $stripped_diff;
-					if ( $diff_ratio > $this->_diff_threshold )
+					$stripped_diff = strlen( strip_tags( $diff ) ) * 2 - $stripped_matches;
+					$diff_ratio    = $stripped_matches / $stripped_diff;
+					if ( $diff_ratio > $this->_diff_threshold ) {
 						continue; // Too different. Don't save diffs.
+					}
 				}
 
 				// Un-inline the diffs by removing del or ins
-				$orig_diffs[$o]  = preg_replace( '|<ins>.*?</ins>|', '', $diff );
-				$final_diffs[$f] = preg_replace( '|<del>.*?</del>|', '', $diff );
+				$orig_diffs[ $o ]  = preg_replace( '|<ins>.*?</ins>|', '', $diff );
+				$final_diffs[ $f ] = preg_replace( '|<del>.*?</del>|', '', $diff );
 			}
 		}
 
-		foreach ( array_keys($orig_rows) as $row ) {
+		foreach ( array_keys( $orig_rows ) as $row ) {
 			// Both columns have blanks. Ignore them.
-			if ( $orig_rows[$row] < 0 && $final_rows[$row] < 0 )
+			if ( $orig_rows[ $row ] < 0 && $final_rows[ $row ] < 0 ) {
 				continue;
+			}
 
 			// If we have a word based diff, use it. Otherwise, use the normal line.
-			if ( isset( $orig_diffs[$orig_rows[$row]] ) )
-				$orig_line = $orig_diffs[$orig_rows[$row]];
-			elseif ( isset( $orig[$orig_rows[$row]] ) )
-				$orig_line = htmlspecialchars($orig[$orig_rows[$row]]);
-			else
+			if ( isset( $orig_diffs[ $orig_rows[ $row ] ] ) ) {
+				$orig_line = $orig_diffs[ $orig_rows[ $row ] ];
+			} elseif ( isset( $orig[ $orig_rows[ $row ] ] ) ) {
+				$orig_line = htmlspecialchars( $orig[ $orig_rows[ $row ] ] );
+			} else {
 				$orig_line = '';
+			}
 
-			if ( isset( $final_diffs[$final_rows[$row]] ) )
-				$final_line = $final_diffs[$final_rows[$row]];
-			elseif ( isset( $final[$final_rows[$row]] ) )
-				$final_line = htmlspecialchars($final[$final_rows[$row]]);
-			else
+			if ( isset( $final_diffs[ $final_rows[ $row ] ] ) ) {
+				$final_line = $final_diffs[ $final_rows[ $row ] ];
+			} elseif ( isset( $final[ $final_rows[ $row ] ] ) ) {
+				$final_line = htmlspecialchars( $final[ $final_rows[ $row ] ] );
+			} else {
 				$final_line = '';
+			}
 
-			if ( $orig_rows[$row] < 0 ) { // Orig is blank. This is really an added row.
-				$r .= $this->_added( array($final_line), false );
-			} elseif ( $final_rows[$row] < 0 ) { // Final is blank. This is really a deleted row.
-				$r .= $this->_deleted( array($orig_line), false );
+			if ( $orig_rows[ $row ] < 0 ) { // Orig is blank. This is really an added row.
+				$r .= $this->_added( array( $final_line ), false );
+			} elseif ( $final_rows[ $row ] < 0 ) { // Final is blank. This is really a deleted row.
+				$r .= $this->_deleted( array( $orig_line ), false );
 			} else { // A true changed row.
 				if ( $this->_show_split_view ) {
 					$r .= '<tr>' . $this->deletedLine( $orig_line ) . $this->emptyLine() . $this->addedLine( $final_line ) . "</tr>\n";
 				} else {
-					$r .= '<tr>' . $this->deletedLine( $orig_line ) . "</tr><tr>" . $this->addedLine( $final_line ) . "</tr>\n";
+					$r .= '<tr>' . $this->deletedLine( $orig_line ) . '</tr><tr>' . $this->addedLine( $final_line ) . "</tr>\n";
 				}
 			}
 		}
@@ -339,80 +359,81 @@
 
 		// Contains all pairwise string comparisons. Keys are such that this need only be a one dimensional array.
 		$matches = array();
-		foreach ( array_keys($orig) as $o ) {
-			foreach ( array_keys($final) as $f ) {
-				$matches["$o,$f"] = $this->compute_string_distance( $orig[$o], $final[$f] );
+		foreach ( array_keys( $orig ) as $o ) {
+			foreach ( array_keys( $final ) as $f ) {
+				$matches[ "$o,$f" ] = $this->compute_string_distance( $orig[ $o ], $final[ $f ] );
 			}
 		}
-		asort($matches); // Order by string distance.
+		asort( $matches ); // Order by string distance.
 
 		$orig_matches  = array();
 		$final_matches = array();
 
 		foreach ( $matches as $keys => $difference ) {
-			list($o, $f) = explode(',', $keys);
-			$o = (int) $o;
-			$f = (int) $f;
+			list($o, $f) = explode( ',', $keys );
+			$o           = (int) $o;
+			$f           = (int) $f;
 
 			// Already have better matches for these guys
-			if ( isset($orig_matches[$o]) && isset($final_matches[$f]) )
+			if ( isset( $orig_matches[ $o ] ) && isset( $final_matches[ $f ] ) ) {
 				continue;
+			}
 
 			// First match for these guys. Must be best match
-			if ( !isset($orig_matches[$o]) && !isset($final_matches[$f]) ) {
-				$orig_matches[$o] = $f;
-				$final_matches[$f] = $o;
+			if ( ! isset( $orig_matches[ $o ] ) && ! isset( $final_matches[ $f ] ) ) {
+				$orig_matches[ $o ]  = $f;
+				$final_matches[ $f ] = $o;
 				continue;
 			}
 
 			// Best match of this final is already taken?  Must mean this final is a new row.
-			if ( isset($orig_matches[$o]) )
-				$final_matches[$f] = 'x';
-
-			// Best match of this orig is already taken?  Must mean this orig is a deleted row.
-			elseif ( isset($final_matches[$f]) )
-				$orig_matches[$o] = 'x';
+			if ( isset( $orig_matches[ $o ] ) ) {
+				$final_matches[ $f ] = 'x';
+			} elseif ( isset( $final_matches[ $f ] ) ) {
+				// Best match of this orig is already taken?  Must mean this orig is a deleted row.
+				$orig_matches[ $o ] = 'x';
+			}
 		}
 
 		// We read the text in this order
-		ksort($orig_matches);
-		ksort($final_matches);
+		ksort( $orig_matches );
+		ksort( $final_matches );
 
 		// Stores rows and blanks for each column.
-		$orig_rows = $orig_rows_copy = array_keys($orig_matches);
-		$final_rows = array_keys($final_matches);
+		$orig_rows  = $orig_rows_copy = array_keys( $orig_matches );
+		$final_rows = array_keys( $final_matches );
 
 		// Interleaves rows with blanks to keep matches aligned.
 		// We may end up with some extraneous blank rows, but we'll just ignore them later.
 		foreach ( $orig_rows_copy as $orig_row ) {
-			$final_pos = array_search($orig_matches[$orig_row], $final_rows, true);
-			$orig_pos = (int) array_search($orig_row, $orig_rows, true);
+			$final_pos = array_search( $orig_matches[ $orig_row ], $final_rows, true );
+			$orig_pos  = (int) array_search( $orig_row, $orig_rows, true );
 
 			if ( false === $final_pos ) { // This orig is paired with a blank final.
 				array_splice( $final_rows, $orig_pos, 0, -1 );
 			} elseif ( $final_pos < $orig_pos ) { // This orig's match is up a ways. Pad final with blank rows.
-				$diff_pos = $final_pos - $orig_pos;
-				while ( $diff_pos < 0 )
-					array_splice( $final_rows, $orig_pos, 0, $diff_pos++ );
+				$diff_array = range( -1, $final_pos - $orig_pos );
+				array_splice( $final_rows, $orig_pos, 0, $diff_array );
 			} elseif ( $final_pos > $orig_pos ) { // This orig's match is down a ways. Pad orig with blank rows.
-				$diff_pos = $orig_pos - $final_pos;
-				while ( $diff_pos < 0 )
-					array_splice( $orig_rows, $orig_pos, 0, $diff_pos++ );
+				$diff_array = range( -1, $orig_pos - $final_pos );
+				array_splice( $orig_rows, $orig_pos, 0, $diff_array );
 			}
 		}
 
 		// Pad the ends with blank rows if the columns aren't the same length
-		$diff_count = count($orig_rows) - count($final_rows);
+		$diff_count = count( $orig_rows ) - count( $final_rows );
 		if ( $diff_count < 0 ) {
-			while ( $diff_count < 0 )
-				array_push($orig_rows, $diff_count++);
+			while ( $diff_count < 0 ) {
+				array_push( $orig_rows, $diff_count++ );
+			}
 		} elseif ( $diff_count > 0 ) {
 			$diff_count = -1 * $diff_count;
-			while ( $diff_count < 0 )
-				array_push($final_rows, $diff_count++);
+			while ( $diff_count < 0 ) {
+				array_push( $final_rows, $diff_count++ );
+			}
 		}
 
-		return array($orig_matches, $final_matches, $orig_rows, $final_rows);
+		return array( $orig_matches, $final_matches, $orig_rows, $final_rows );
 	}
 
 	/**
@@ -425,19 +446,36 @@
 	 * @return int
 	 */
 	public function compute_string_distance( $string1, $string2 ) {
-		// Vectors containing character frequency for all chars in each string
-		$chars1 = count_chars($string1);
-		$chars2 = count_chars($string2);
+		// Use an md5 hash of the strings for a count cache, as it's fast to generate, and collisions aren't a concern.
+		$count_key1 = md5( $string1 );
+		$count_key2 = md5( $string2 );
 
-		// L1-norm of difference vector.
-		$difference = array_sum( array_map( array($this, 'difference'), $chars1, $chars2 ) );
+		// Cache vectors containing character frequency for all chars in each string.
+		if ( ! isset( $this->count_cache[ $count_key1 ] ) ) {
+			$this->count_cache[ $count_key1 ] = count_chars( $string1 );
+		}
+		if ( ! isset( $this->count_cache[ $count_key2 ] ) ) {
+			$this->count_cache[ $count_key2 ] = count_chars( $string2 );
+		}
+
+		$chars1 = $this->count_cache[ $count_key1 ];
+		$chars2 = $this->count_cache[ $count_key2 ];
+
+		$difference_key = md5( implode( ',', $chars1 ) . ':' . implode( ',', $chars2 ) );
+		if ( ! isset( $this->difference_cache[ $difference_key ] ) ) {
+			// L1-norm of difference vector.
+			$this->difference_cache[ $difference_key ] = array_sum( array_map( array( $this, 'difference' ), $chars1, $chars2 ) );
+		}
+
+		$difference = $this->difference_cache[ $difference_key ];
 
 		// $string1 has zero length? Odd. Give huge penalty by not dividing.
-		if ( !$string1 )
+		if ( ! $string1 ) {
 			return $difference;
+		}
 
 		// Return distance per character (of string1).
-		return $difference / strlen($string1);
+		return $difference / strlen( $string1 );
 	}
 
 	/**