src/Diff.php
public function cleanupEfficiency() {
        $diffs = $this->getChanges();

        $changes = false;
        // Stack of indices where equalities are found.
        $equalities = array();
        // Always equal to diffs[equalities[-1]][1]
        $lastequality = null;
        // Index of current position.
        $pointer = 0;
        // Is there an insertion operation before the last equality.
        $pre_ins = false;
        // Is there a deletion operation before the last equality.
        $pre_del = false;
        // Is there an insertion operation after the last equality.
        $post_ins = false;
        // Is there a deletion operation after the last equality.
        $post_del = false;

        while ($pointer < count($diffs)) {
            if ($diffs[$pointer][0] == self::EQUAL) {
                if (mb_strlen($diffs[$pointer][1]) < $this->getEditCost() && ($post_ins || $post_del)) {
                    // Candidate found.
                    $equalities[] = $pointer;
                    $pre_ins = $post_ins;
                    $pre_del = $post_del;
                    $lastequality = $diffs[$pointer][1];
                } else {
                    // Not a candidate, and can never become one.
                    $equalities = array();
                    $lastequality = null;
                }
                $post_ins = false;
                $post_del = false;
            } else {
                if ($diffs[$pointer][0] == self::DELETE) {
                    $post_del = true;
                } else {
                    $post_ins = true;
                }

                // Five types to be split:
                // <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
                // <ins>A</ins>X<ins>C</ins><del>D</del>
                // <ins>A</ins><del>B</del>X<ins>C</ins>
                // <ins>A</del>X<ins>C</ins><del>D</del>
                // <ins>A</ins><del>B</del>X<del>C</del>
                // TODO refactor condition
                if (
                    $lastequality != '' &&
                    (
                        ($pre_ins && $pre_del && $post_ins && $post_del) ||
                        (
                            mb_strlen($lastequality) < $this->getEditCost() / 2 &&
                            ($pre_ins + $pre_del + $post_del + $post_ins == 3)
                        )
                    )
                ) {
                    $insertPointer = array_pop($equalities);
                    // Duplicate record.
                    array_splice($diffs, $insertPointer, 0, array(array(
                        self::DELETE,
                        $lastequality,
                    )));
                    // Change second copy to insert.
                    $diffs[$insertPointer + 1][0] = self::INSERT;
                    // Throw away the previous equality (it needs to be reevaluated).
                    if (count($equalities)) {
                        array_pop($equalities);
                    }
                    $lastequality = null;
                    if ($pre_ins && $pre_del) {
                        // No changes made which could affect previous entry, keep going.
                        $post_ins = true;
                        $post_del = true;
                        $equalities = array();
                    } else {
                        if (count($equalities)) {
                            // Throw away the previous equality.
                            array_pop($equalities);
                        }
                        if (count($equalities)) {
                            $pointer = end($equalities);
                        } else {
                            $pointer = -1;
                        }
                        $post_ins = false;
                        $post_del = false;
                    }
                    $changes = true;
                }
            }
            $pointer++;
        }
        $this->setChanges($diffs);

        if ($changes) {
            $this->cleanupMerge();
        }

        return $this;
    }
public function cleanupEfficiency() {
        $diffs = $this->getChanges();

        $changes = false;
        // Stack of indices where equalities are found.
        $equalities = array();
        // Always equal to diffs[equalities[-1]][1]
        $lastequality = null;
        // Index of current position.
        $pointer = 0;
        // Is there an insertion operation before the last equality.
        $pre_ins = false;
        // Is there a deletion operation before the last equality.
        $pre_del = false;
        // Is there an insertion operation after the last equality.
        $post_ins = false;
        // Is there a deletion operation after the last equality.
        $post_del = false;

        while ($pointer < count($diffs)) {
            if ($diffs[$pointer][0] == self::EQUAL) {
                if (mb_strlen($diffs[$pointer][1]) < $this->getEditCost() && ($post_ins || $post_del)) {
                    // Candidate found.
                    $equalities[] = $pointer;
                    $pre_ins = $post_ins;
                    $pre_del = $post_del;
                    $lastequality = $diffs[$pointer][1];
                } else {
                    // Not a candidate, and can never become one.
                    $equalities = array();
                    $lastequality = null;
                }
                $post_ins = false;
                $post_del = false;
            } else {
                if ($diffs[$pointer][0] == self::DELETE) {
                    $post_del = true;
                } else {
                    $post_ins = true;
                }

                // Five types to be split:
                // <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
                // <ins>A</ins>X<ins>C</ins><del>D</del>
                // <ins>A</ins><del>B</del>X<ins>C</ins>
                // <ins>A</del>X<ins>C</ins><del>D</del>
                // <ins>A</ins><del>B</del>X<del>C</del>
                // TODO refactor condition
                if (
                    $lastequality != '' &&
                    (
                        ($pre_ins && $pre_del && $post_ins && $post_del) ||
                        (
                            mb_strlen($lastequality) < $this->getEditCost() / 2 &&
                            ($pre_ins + $pre_del + $post_del + $post_ins == 3)
                        )
                    )
                ) {
                    $insertPointer = array_pop($equalities);
                    // Duplicate record.
                    array_splice($diffs, $insertPointer, 0, array(array(
                        self::DELETE,
                        $lastequality,
                    )));
                    // Change second copy to insert.
                    $diffs[$insertPointer + 1][0] = self::INSERT;
                    // Throw away the previous equality (it needs to be reevaluated).
                    if (count($equalities)) {
                        array_pop($equalities);
                    }
                    $lastequality = null;
                    if ($pre_ins && $pre_del) {
                        // No changes made which could affect previous entry, keep going.
                        $post_ins = true;
                        $post_del = true;
                        $equalities = array();
                    } else {
                        if (count($equalities)) {
                            // Throw away the previous equality.
                            array_pop($equalities);
                        }
                        if (count($equalities)) {
                            $pointer = end($equalities);
                        } else {
                            $pointer = -1;
                        }
                        $post_ins = false;
                        $post_del = false;
                    }
                    $changes = true;
                }
            }
            $pointer++;
        }
        $this->setChanges($diffs);

        if ($changes) {
            $this->cleanupMerge();
        }

        return $this;
    }
Reduce the number of edits by eliminating operationally trivial equalities.
TODO refactor this Cap's code

@return $this