Class PikeVM

classpath/java/util/regex/PikeVM.java:18–629

A minimal implementation of a regular expression engine. @author Johannes Schindelin

 * @author Johannes Schindelin
 */
class PikeVM implements PikeVMOpcodes {
  private final int[] program;
  private final int groupCount;
  private final int offsetsCount;
  /*
   * For find(), we do not want to anchor the match at the start offset. Our
   * compiler allows this by prefixing the code with an implicit '(?:.*?)'. For
   * regular matches() calls, we want to skip that code and start at {@code
   * findPrefixLength} instead.
   */
  private final int findPrefixLength;
  private final CharacterMatcher[] classes;
  private final PikeVM[] lookarounds;
  private final static CharacterMatcher wordCharacter =
    CharacterMatcher.parse("\\w");
  private final static CharacterMatcher lineTerminator =
    CharacterMatcher.parse("[\n\r\u0085\u2028\u2029]");
  private boolean multiLine;

  public interface Result {
    void set(int[] start, int[] end);
  }

  protected PikeVM(int[] program, int findPrefixLength, int groupCount,
    CharacterMatcher[] classes, PikeVM[] lookarounds)
  {
    this.program = program;
    this.findPrefixLength = findPrefixLength;
    this.groupCount = groupCount;
    offsetsCount = 2 * groupCount + 2;
    this.classes = classes;
    this.lookarounds = lookarounds;
  }

  /**
   * The current thread states.
   * <p>
   * The threads are identified by their program counter. The rationale: as all
   * threads are executed in lock-step, i.e. for the same character in the
   * string to be matched, it does not make sense for two threads to be at the
   * same program counter -- they would both do exactly the same for the rest of
   * the execution.
   * </p>
   * <p>
   * For efficiency, the threads are kept in a linked list that actually lives
   * in an array indexed by the program counter, pointing to the next thread's
   * program counter, in the order of high to low priority.
   * </p>
   * <p>
   * Program counters which have no thread associated thread are marked as -1.
   * The program counter associated with the least-priority thread (the last one
   * in the linked list) is marked as -2 to be able to tell it apart from
   * unscheduled threads.
   * </p>
   * <p>
   * We actually never need to have an explicit value for the priority, the
   * ordering is sufficient: whenever a new thread is to be scheduled and it is
   * found to be scheduled already, it was already scheduled by a