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WalkerFactory.javaAPI DocJava SE 6 API60341Tue Jun 10 00:23:14 BST 2008com.sun.org.apache.xpath.internal.axes

WalkerFactory

public class WalkerFactory extends Object
This class is both a factory for XPath location path expressions, which are built from the opcode map output, and an analysis engine for the location path expressions in order to provide optimization hints.

Fields Summary
static final boolean
DEBUG_PATTERN_CREATION
Set to true for diagnostics about walker creation
static final boolean
DEBUG_WALKER_CREATION
Set to true for diagnostics about walker creation
static final boolean
DEBUG_ITERATOR_CREATION
Set to true for diagnostics about iterator creation
public static final int
BITS_COUNT
First 8 bits are the number of top-level location steps. Hopefully there will never be more that 255 location steps!!!
public static final int
BITS_RESERVED
4 bits are reserved for future use.
public static final int
BIT_PREDICATE
Bit is on if the expression contains a top-level predicate.
public static final int
BIT_ANCESTOR
Bit is on if any of the walkers contain an ancestor step.
public static final int
BIT_ANCESTOR_OR_SELF
Bit is on if any of the walkers contain an ancestor-or-self step.
public static final int
BIT_ATTRIBUTE
Bit is on if any of the walkers contain an attribute step.
public static final int
BIT_CHILD
Bit is on if any of the walkers contain a child step.
public static final int
BIT_DESCENDANT
Bit is on if any of the walkers contain a descendant step.
public static final int
BIT_DESCENDANT_OR_SELF
Bit is on if any of the walkers contain a descendant-or-self step.
public static final int
BIT_FOLLOWING
Bit is on if any of the walkers contain a following step.
public static final int
BIT_FOLLOWING_SIBLING
Bit is on if any of the walkers contain a following-sibiling step.
public static final int
BIT_NAMESPACE
Bit is on if any of the walkers contain a namespace step.
public static final int
BIT_PARENT
Bit is on if any of the walkers contain a parent step.
public static final int
BIT_PRECEDING
Bit is on if any of the walkers contain a preceding step.
public static final int
BIT_PRECEDING_SIBLING
Bit is on if any of the walkers contain a preceding-sibling step.
public static final int
BIT_SELF
Bit is on if any of the walkers contain a self step.
public static final int
BIT_FILTER
Bit is on if any of the walkers contain a filter (i.e. id(), extension function, etc.) step.
public static final int
BIT_ROOT
Bit is on if any of the walkers contain a root step.
public static final int
BITMASK_TRAVERSES_OUTSIDE_SUBTREE
If any of these bits are on, the expression may likely traverse outside the given subtree.
public static final int
BIT_BACKWARDS_SELF
Bit is on if any of the walkers can go backwards in document order from the context node.
public static final int
BIT_ANY_DESCENDANT_FROM_ROOT
Found "//foo" pattern
public static final int
BIT_NODETEST_ANY
Bit is on if any of the walkers contain an node() test. This is really only useful if the count is 1.
public static final int
BIT_MATCH_PATTERN
Bit is on if the expression is a match pattern.
Constructors Summary
Methods Summary
private static intanalyze(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos, int stepIndex)
Analyze the location path and return 32 bits that give information about the location path as a whole. See the BIT_XXX constants for meaning about each of the bits.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
param
stepIndex The top-level step index withing the iterator.
return
32 bits as an integer that give information about the location path as a whole.
throws
javax.xml.transform.TransformerException


    int stepType;
    int stepCount = 0;
    int analysisResult = 0x00000000;  // 32 bits of analysis

    while (OpCodes.ENDOP != (stepType = compiler.getOp(stepOpCodePos)))
    {
      stepCount++;

      // String namespace = compiler.getStepNS(stepOpCodePos);
      // boolean isNSWild = (null != namespace) 
      //                   ? namespace.equals(NodeTest.WILD) : false;
      // String localname = compiler.getStepLocalName(stepOpCodePos);
      // boolean isWild = (null != localname) ? localname.equals(NodeTest.WILD) : false;
      boolean predAnalysis = analyzePredicate(compiler, stepOpCodePos,
                                              stepType);

      if (predAnalysis)
        analysisResult |= BIT_PREDICATE;

      switch (stepType)
      {
      case OpCodes.OP_VARIABLE :
      case OpCodes.OP_EXTFUNCTION :
      case OpCodes.OP_FUNCTION :
      case OpCodes.OP_GROUP :
        analysisResult |= BIT_FILTER;
        break;
      case OpCodes.FROM_ROOT :
        analysisResult |= BIT_ROOT;
        break;
      case OpCodes.FROM_ANCESTORS :
        analysisResult |= BIT_ANCESTOR;
        break;
      case OpCodes.FROM_ANCESTORS_OR_SELF :
        analysisResult |= BIT_ANCESTOR_OR_SELF;
        break;
      case OpCodes.FROM_ATTRIBUTES :
        analysisResult |= BIT_ATTRIBUTE;
        break;
      case OpCodes.FROM_NAMESPACE :
        analysisResult |= BIT_NAMESPACE;
        break;
      case OpCodes.FROM_CHILDREN :
        analysisResult |= BIT_CHILD;
        break;
      case OpCodes.FROM_DESCENDANTS :
        analysisResult |= BIT_DESCENDANT;
        break;
      case OpCodes.FROM_DESCENDANTS_OR_SELF :

        // Use a special bit to to make sure we get the right analysis of "//foo".
        if (2 == stepCount && BIT_ROOT == analysisResult)
        {
          analysisResult |= BIT_ANY_DESCENDANT_FROM_ROOT;
        }

        analysisResult |= BIT_DESCENDANT_OR_SELF;
        break;
      case OpCodes.FROM_FOLLOWING :
        analysisResult |= BIT_FOLLOWING;
        break;
      case OpCodes.FROM_FOLLOWING_SIBLINGS :
        analysisResult |= BIT_FOLLOWING_SIBLING;
        break;
      case OpCodes.FROM_PRECEDING :
        analysisResult |= BIT_PRECEDING;
        break;
      case OpCodes.FROM_PRECEDING_SIBLINGS :
        analysisResult |= BIT_PRECEDING_SIBLING;
        break;
      case OpCodes.FROM_PARENT :
        analysisResult |= BIT_PARENT;
        break;
      case OpCodes.FROM_SELF :
        analysisResult |= BIT_SELF;
        break;
      case OpCodes.MATCH_ATTRIBUTE :
        analysisResult |= (BIT_MATCH_PATTERN | BIT_ATTRIBUTE);
        break;
      case OpCodes.MATCH_ANY_ANCESTOR :
        analysisResult |= (BIT_MATCH_PATTERN | BIT_ANCESTOR);
        break;
      case OpCodes.MATCH_IMMEDIATE_ANCESTOR :
        analysisResult |= (BIT_MATCH_PATTERN | BIT_PARENT);
        break;
      default :
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                                   //+ stepType);
      }

      if (OpCodes.NODETYPE_NODE == compiler.getOp(stepOpCodePos + 3))  // child::node()
      {
        analysisResult |= BIT_NODETEST_ANY;
      }

      stepOpCodePos = compiler.getNextStepPos(stepOpCodePos);

      if (stepOpCodePos < 0)
        break;
    }

    analysisResult |= (stepCount & BITS_COUNT);

    return analysisResult;
static booleananalyzePredicate(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos, int stepType)
Analyze a step and give information about it's predicates. Right now this just returns true or false if the step has a predicate.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
opPos The opcode position for the step.
param
stepType The type of step, one of OP_GROUP, etc.
return
true if step has a predicate.
throws
javax.xml.transform.TransformerException


    int argLen;

    switch (stepType)
    {
    case OpCodes.OP_VARIABLE :
    case OpCodes.OP_EXTFUNCTION :
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_GROUP :
      argLen = compiler.getArgLength(opPos);
      break;
    default :
      argLen = compiler.getArgLengthOfStep(opPos);
    }

    int pos = compiler.getFirstPredicateOpPos(opPos);
    int nPredicates = compiler.countPredicates(pos);

    return (nPredicates > 0) ? true : false;
public static booleancanCrissCross(int analysis)

    // This could be done faster.  Coded for clarity.
    if(walksSelfOnly(analysis))
      return false;
    else if(walksDownOnly(analysis) && !canSkipSubtrees(analysis))
      return false;
    else if(walksChildrenAndExtraAndSelfOnly(analysis))
      return false;
    else if(walksDescendantsAndExtraAndSelfOnly(analysis))
      return false;
    else if(walksUpOnly(analysis))
      return false;
    else if(walksExtraNodesOnly(analysis))
      return false;
    else if(walksSubtree(analysis) 
           && (walksSideways(analysis) 
            || walksUp(analysis) 
            || canSkipSubtrees(analysis)))
      return true;
    else
      return false;
public static booleancanSkipSubtrees(int analysis)

    return isSet(analysis, BIT_CHILD) | walksSideways(analysis);
private static com.sun.org.apache.xpath.internal.patterns.StepPatterncreateDefaultStepPattern(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos, com.sun.org.apache.xpath.internal.axes.MatchPatternIterator mpi, int analysis, com.sun.org.apache.xpath.internal.patterns.StepPattern tail, com.sun.org.apache.xpath.internal.patterns.StepPattern head)
Create a StepPattern that is contained within a LocationPath.

param
compiler The compiler that holds the syntax tree/op map to construct from.
param
stepOpCodePos The current op code position within the opmap.
param
mpi The MatchPatternIterator to which the steps will be attached.
param
analysis 32 bits of analysis, from which the type of AxesWalker may be influenced.
param
tail The step that is the first step analyzed, but the last step in the relative match linked list, i.e. the tail. May be null.
param
head The step that is the current head of the relative match step linked list. May be null.
return
the head of the list.
throws
javax.xml.transform.TransformerException


    int stepType = compiler.getOp(opPos);
    boolean simpleInit = false;
    int totalNumberWalkers = (analysis & BITS_COUNT);
    boolean prevIsOneStepDown = true;
    int firstStepPos = compiler.getFirstChildPos(opPos);
    
    int whatToShow = compiler.getWhatToShow(opPos);
    StepPattern ai = null;
    int axis, predicateAxis;
    
    switch (stepType)
    {
    case OpCodes.OP_VARIABLE :
    case OpCodes.OP_EXTFUNCTION :
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_GROUP :
      prevIsOneStepDown = false;

      Expression expr;

      switch (stepType)
      {
      case OpCodes.OP_VARIABLE :
      case OpCodes.OP_EXTFUNCTION :
      case OpCodes.OP_FUNCTION :
      case OpCodes.OP_GROUP :
        expr = compiler.compile(opPos);
        break;
      default :
        expr = compiler.compile(opPos + 2);
      }

      axis = Axis.FILTEREDLIST;
      predicateAxis = Axis.FILTEREDLIST;
      ai = new FunctionPattern(expr, axis, predicateAxis);
      simpleInit = true;
      break;
    case OpCodes.FROM_ROOT :
      whatToShow = DTMFilter.SHOW_DOCUMENT
                   | DTMFilter.SHOW_DOCUMENT_FRAGMENT;

      axis = Axis.ROOT;
      predicateAxis = Axis.ROOT;
      ai = new StepPattern(DTMFilter.SHOW_DOCUMENT | 
                                DTMFilter.SHOW_DOCUMENT_FRAGMENT,
                                axis, predicateAxis);
      break;
    case OpCodes.FROM_ATTRIBUTES :
      whatToShow = DTMFilter.SHOW_ATTRIBUTE;
      axis = Axis.PARENT;
      predicateAxis = Axis.ATTRIBUTE;
      // ai = new StepPattern(whatToShow, Axis.SELF, Axis.SELF);
      break;
    case OpCodes.FROM_NAMESPACE :
      whatToShow = DTMFilter.SHOW_NAMESPACE;
      axis = Axis.PARENT;
      predicateAxis = Axis.NAMESPACE;
      // ai = new StepPattern(whatToShow, axis, predicateAxis);
      break;
    case OpCodes.FROM_ANCESTORS :
      axis = Axis.DESCENDANT;
      predicateAxis = Axis.ANCESTOR;
      break;
    case OpCodes.FROM_CHILDREN :
      axis = Axis.PARENT;
      predicateAxis = Axis.CHILD;
      break;
    case OpCodes.FROM_ANCESTORS_OR_SELF :
      axis = Axis.DESCENDANTORSELF;
      predicateAxis = Axis.ANCESTORORSELF;
      break;
    case OpCodes.FROM_SELF :
      axis = Axis.SELF;
      predicateAxis = Axis.SELF;
      break;
    case OpCodes.FROM_PARENT :
      axis = Axis.CHILD;
      predicateAxis = Axis.PARENT;
      break;
    case OpCodes.FROM_PRECEDING_SIBLINGS :
      axis = Axis.FOLLOWINGSIBLING;
      predicateAxis = Axis.PRECEDINGSIBLING;
      break;
    case OpCodes.FROM_PRECEDING :
      axis = Axis.FOLLOWING;
      predicateAxis = Axis.PRECEDING;
      break;
    case OpCodes.FROM_FOLLOWING_SIBLINGS :
      axis = Axis.PRECEDINGSIBLING;
      predicateAxis = Axis.FOLLOWINGSIBLING;
      break;
    case OpCodes.FROM_FOLLOWING :
      axis = Axis.PRECEDING;
      predicateAxis = Axis.FOLLOWING;
      break;
    case OpCodes.FROM_DESCENDANTS_OR_SELF :
      axis = Axis.ANCESTORORSELF;
      predicateAxis = Axis.DESCENDANTORSELF;
      break;
    case OpCodes.FROM_DESCENDANTS :
      axis = Axis.ANCESTOR;
      predicateAxis = Axis.DESCENDANT;
      break;
    default :
      throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                                 //+ stepType);
    }
    if(null == ai)
    {
      whatToShow = compiler.getWhatToShow(opPos); // %REVIEW%
      ai = new StepPattern(whatToShow, compiler.getStepNS(opPos),
                                compiler.getStepLocalName(opPos),
                                axis, predicateAxis);
    }
   
    if (false || DEBUG_PATTERN_CREATION)
    {
      System.out.print("new step: "+ ai);
      System.out.print(", axis: " + Axis.getNames(ai.getAxis()));
      System.out.print(", predAxis: " + Axis.getNames(ai.getAxis()));
      System.out.print(", what: ");
      System.out.print("    ");
      ai.debugWhatToShow(ai.getWhatToShow());
    }

    int argLen = compiler.getFirstPredicateOpPos(opPos);

    ai.setPredicates(compiler.getCompiledPredicates(argLen));

    return ai;
private static com.sun.org.apache.xpath.internal.axes.AxesWalkercreateDefaultWalker(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos, com.sun.org.apache.xpath.internal.axes.WalkingIterator lpi, int analysis)
Create the proper Walker from the axes type.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
opPos The opcode position for the step.
param
lpi The owning location path iterator.
param
analysis 32 bits of analysis, from which the type of AxesWalker may be influenced.
return
non-null reference to AxesWalker derivative.
throws
RuntimeException if the input is bad.


    AxesWalker ai = null;
    int stepType = compiler.getOp(opPos);

    /*
    System.out.println("0: "+compiler.getOp(opPos));
    System.out.println("1: "+compiler.getOp(opPos+1));
    System.out.println("2: "+compiler.getOp(opPos+2));
    System.out.println("3: "+compiler.getOp(opPos+3));
    System.out.println("4: "+compiler.getOp(opPos+4));
    System.out.println("5: "+compiler.getOp(opPos+5));
    */
    boolean simpleInit = false;
    int totalNumberWalkers = (analysis & BITS_COUNT);
    boolean prevIsOneStepDown = true;

    switch (stepType)
    {
    case OpCodes.OP_VARIABLE :
    case OpCodes.OP_EXTFUNCTION :
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_GROUP :
      prevIsOneStepDown = false;

      if (DEBUG_WALKER_CREATION)
        System.out.println("new walker:  FilterExprWalker: " + analysis
                           + ", " + compiler.toString());

      ai = new FilterExprWalker(lpi);
      simpleInit = true;
      break;
    case OpCodes.FROM_ROOT :
      ai = new AxesWalker(lpi, Axis.ROOT);
      break;
    case OpCodes.FROM_ANCESTORS :
      prevIsOneStepDown = false;
      ai = new ReverseAxesWalker(lpi, Axis.ANCESTOR);
      break;
    case OpCodes.FROM_ANCESTORS_OR_SELF :
      prevIsOneStepDown = false;
      ai = new ReverseAxesWalker(lpi, Axis.ANCESTORORSELF);
      break;
    case OpCodes.FROM_ATTRIBUTES :
      ai = new AxesWalker(lpi, Axis.ATTRIBUTE);
      break;
    case OpCodes.FROM_NAMESPACE :
      ai = new AxesWalker(lpi, Axis.NAMESPACE);
      break;
    case OpCodes.FROM_CHILDREN :
      ai = new AxesWalker(lpi, Axis.CHILD);
      break;
    case OpCodes.FROM_DESCENDANTS :
      prevIsOneStepDown = false;
      ai = new AxesWalker(lpi, Axis.DESCENDANT);
      break;
    case OpCodes.FROM_DESCENDANTS_OR_SELF :
      prevIsOneStepDown = false;
      ai = new AxesWalker(lpi, Axis.DESCENDANTORSELF);
      break;
    case OpCodes.FROM_FOLLOWING :
      prevIsOneStepDown = false;
      ai = new AxesWalker(lpi, Axis.FOLLOWING);
      break;
    case OpCodes.FROM_FOLLOWING_SIBLINGS :
      prevIsOneStepDown = false;
      ai = new AxesWalker(lpi, Axis.FOLLOWINGSIBLING);
      break;
    case OpCodes.FROM_PRECEDING :
      prevIsOneStepDown = false;
      ai = new ReverseAxesWalker(lpi, Axis.PRECEDING);
      break;
    case OpCodes.FROM_PRECEDING_SIBLINGS :
      prevIsOneStepDown = false;
      ai = new ReverseAxesWalker(lpi, Axis.PRECEDINGSIBLING);
      break;
    case OpCodes.FROM_PARENT :
      prevIsOneStepDown = false;
      ai = new ReverseAxesWalker(lpi, Axis.PARENT);
      break;
    case OpCodes.FROM_SELF :
      ai = new AxesWalker(lpi, Axis.SELF);
      break;
    default :
      throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                                 //+ stepType);
    }

    if (simpleInit)
    {
      ai.initNodeTest(DTMFilter.SHOW_ALL);
    }
    else
    {
      int whatToShow = compiler.getWhatToShow(opPos);

      /*
      System.out.print("construct: ");
      NodeTest.debugWhatToShow(whatToShow);
      System.out.println("or stuff: "+(whatToShow & (DTMFilter.SHOW_ATTRIBUTE
                             | DTMFilter.SHOW_ELEMENT
                             | DTMFilter.SHOW_PROCESSING_INSTRUCTION)));
      */
      if ((0 == (whatToShow
                 & (DTMFilter.SHOW_ATTRIBUTE | DTMFilter.SHOW_NAMESPACE | DTMFilter.SHOW_ELEMENT
                    | DTMFilter.SHOW_PROCESSING_INSTRUCTION))) || (whatToShow == DTMFilter.SHOW_ALL))
        ai.initNodeTest(whatToShow);
      else
      {
        ai.initNodeTest(whatToShow, compiler.getStepNS(opPos),
                        compiler.getStepLocalName(opPos));
      }
    }

    return ai;
public static voiddiagnoseIterator(java.lang.String name, int analysis, com.sun.org.apache.xpath.internal.compiler.Compiler compiler)

    System.out.println(compiler.toString()+", "+name+", "
                             + Integer.toBinaryString(analysis) + ", "
                             + getAnalysisString(analysis));
static booleanfunctionProximateOrContainsProximate(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos)

    int endFunc = opPos + compiler.getOp(opPos + 1) - 1;
    opPos = compiler.getFirstChildPos(opPos);
    int funcID = compiler.getOp(opPos);
    //  System.out.println("funcID: "+funcID);
    //  System.out.println("opPos: "+opPos);
    //  System.out.println("endFunc: "+endFunc);
    switch(funcID)
    {
      case FunctionTable.FUNC_LAST:
      case FunctionTable.FUNC_POSITION:
        return true;
      default:
        opPos++;
        int i = 0;
        for (int p = opPos; p < endFunc; p = compiler.getNextOpPos(p), i++)
        {
          int innerExprOpPos = p+2;
          int argOp = compiler.getOp(innerExprOpPos);
          boolean prox = isProximateInnerExpr(compiler, innerExprOpPos);
          if(prox)
            return true;
        }

    }
    return false;
public static intgetAnalysisBitFromAxes(int axis)
Get a corresponding BIT_XXX from an axis.

param
axis One of Axis.ANCESTOR, etc.
return
One of BIT_ANCESTOR, etc.

      switch (axis) // Generate new traverser
        {
        case Axis.ANCESTOR :
          return BIT_ANCESTOR;
        case Axis.ANCESTORORSELF :
          return BIT_ANCESTOR_OR_SELF;
        case Axis.ATTRIBUTE :
          return BIT_ATTRIBUTE;
        case Axis.CHILD :
          return BIT_CHILD;
        case Axis.DESCENDANT :
          return BIT_DESCENDANT;
        case Axis.DESCENDANTORSELF :
          return BIT_DESCENDANT_OR_SELF;
        case Axis.FOLLOWING :
          return BIT_FOLLOWING;
        case Axis.FOLLOWINGSIBLING :
          return BIT_FOLLOWING_SIBLING;
        case Axis.NAMESPACE :
        case Axis.NAMESPACEDECLS :
          return BIT_NAMESPACE;
        case Axis.PARENT :
          return BIT_PARENT;
        case Axis.PRECEDING :
          return BIT_PRECEDING;
        case Axis.PRECEDINGSIBLING :
          return BIT_PRECEDING_SIBLING;
        case Axis.SELF :
          return BIT_SELF;
        case Axis.ALLFROMNODE :
          return BIT_DESCENDANT_OR_SELF;
          // case Axis.PRECEDINGANDANCESTOR :
        case Axis.DESCENDANTSFROMROOT :
        case Axis.ALL :
        case Axis.DESCENDANTSORSELFFROMROOT :
          return BIT_ANY_DESCENDANT_FROM_ROOT;
        case Axis.ROOT :
          return BIT_ROOT;
        case Axis.FILTEREDLIST :
          return BIT_FILTER;
        default :
          return BIT_FILTER;
      }
public static java.lang.StringgetAnalysisString(int analysis)

    StringBuffer buf = new StringBuffer();
    buf.append("count: "+getStepCount(analysis)+" ");
    if((analysis & BIT_NODETEST_ANY) != 0)
    {
      buf.append("NTANY|");
    }
    if((analysis & BIT_PREDICATE) != 0)
    {
      buf.append("PRED|");
    }
    if((analysis & BIT_ANCESTOR) != 0)
    {
      buf.append("ANC|");
    }
    if((analysis & BIT_ANCESTOR_OR_SELF) != 0)
    {
      buf.append("ANCOS|");
    }
    if((analysis & BIT_ATTRIBUTE) != 0)
    {
      buf.append("ATTR|");
    }
    if((analysis & BIT_CHILD) != 0)
    {
      buf.append("CH|");
    }
    if((analysis & BIT_DESCENDANT) != 0)
    {
      buf.append("DESC|");
    }
    if((analysis & BIT_DESCENDANT_OR_SELF) != 0)
    {
      buf.append("DESCOS|");
    }
    if((analysis & BIT_FOLLOWING) != 0)
    {
      buf.append("FOL|");
    }
    if((analysis & BIT_FOLLOWING_SIBLING) != 0)
    {
      buf.append("FOLS|");
    }
    if((analysis & BIT_NAMESPACE) != 0)
    {
      buf.append("NS|");
    }
    if((analysis & BIT_PARENT) != 0)
    {
      buf.append("P|");
    }
    if((analysis & BIT_PRECEDING) != 0)
    {
      buf.append("PREC|");
    }
    if((analysis & BIT_PRECEDING_SIBLING) != 0)
    {
      buf.append("PRECS|");
    }
    if((analysis & BIT_SELF) != 0)
    {
      buf.append(".|");
    }
    if((analysis & BIT_FILTER) != 0)
    {
      buf.append("FLT|");
    }
    if((analysis & BIT_ROOT) != 0)
    {
      buf.append("R|");
    }
    return buf.toString();
public static intgetAxisFromStep(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos)
Special purpose function to see if we can optimize the pattern for a DescendantIterator.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
return
32 bits as an integer that give information about the location path as a whole.
throws
javax.xml.transform.TransformerException


    int stepType = compiler.getOp(stepOpCodePos);

    switch (stepType)
    {
    case OpCodes.FROM_FOLLOWING :
      return Axis.FOLLOWING;
    case OpCodes.FROM_FOLLOWING_SIBLINGS :
      return Axis.FOLLOWINGSIBLING;
    case OpCodes.FROM_PRECEDING :
      return Axis.PRECEDING;
    case OpCodes.FROM_PRECEDING_SIBLINGS :
      return Axis.PRECEDINGSIBLING;
    case OpCodes.FROM_PARENT :
      return Axis.PARENT;
    case OpCodes.FROM_NAMESPACE :
      return Axis.NAMESPACE;
    case OpCodes.FROM_ANCESTORS :
      return Axis.ANCESTOR;
    case OpCodes.FROM_ANCESTORS_OR_SELF :
      return Axis.ANCESTORORSELF;
    case OpCodes.FROM_ATTRIBUTES :
      return Axis.ATTRIBUTE;
    case OpCodes.FROM_ROOT :
      return Axis.ROOT;
    case OpCodes.FROM_CHILDREN :
      return Axis.CHILD;
    case OpCodes.FROM_DESCENDANTS_OR_SELF :
      return Axis.DESCENDANTORSELF;
    case OpCodes.FROM_DESCENDANTS :
      return Axis.DESCENDANT;
    case OpCodes.FROM_SELF :
      return Axis.SELF;
    case OpCodes.OP_EXTFUNCTION :
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_GROUP :
    case OpCodes.OP_VARIABLE :
      return Axis.FILTEREDLIST;
    }

    throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                               //+ stepType);
public static intgetStepCount(int analysis)

    return (analysis & BITS_COUNT);
public static booleanhasPredicate(int analysis)

  
      
  
    return (0 != (analysis & BIT_PREDICATE));
public static booleanisAbsolute(int analysis)

    return isSet(analysis, BIT_ROOT | BIT_FILTER);
public static booleanisDownwardAxisOfMany(int axis)
Tell if the given axis goes downword. Bogus name, if you can think of a better one, please do tell. This really has to do with inverting attribute axis.

param
axis One of Axis.XXX.
return
true if the axis is not a child axis and does not go up from the axis root.

    return ((Axis.DESCENDANTORSELF == axis) ||
          (Axis.DESCENDANT == axis) 
          || (Axis.FOLLOWING == axis) 
//          || (Axis.FOLLOWINGSIBLING == axis) 
          || (Axis.PRECEDING == axis) 
//          || (Axis.PRECEDINGSIBLING == axis)
          );
public static booleanisNaturalDocOrder(int analysis)
Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.

param
analysis The general analysis of the pattern.
return
true if the walk can be done in natural order.
throws
javax.xml.transform.TransformerException

    if(canCrissCross(analysis) || isSet(analysis, BIT_NAMESPACE) ||
       walksFilteredList(analysis))
      return false;
      
    if(walksInDocOrder(analysis))
      return true;
      
    return false;
private static booleanisNaturalDocOrder(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos, int stepIndex, int analysis)
Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
param
stepIndex The top-level step index withing the iterator.
param
analysis The general analysis of the pattern.
return
true if the walk can be done in natural order.
throws
javax.xml.transform.TransformerException

    if(canCrissCross(analysis))
      return false;
      
    // Namespaces can present some problems, so just punt if we're looking for 
    // these.
    if(isSet(analysis, BIT_NAMESPACE))
      return false;
      
    // The following, preceding, following-sibling, and preceding sibling can 
    // be found in doc order if we get to this point, but if they occur 
    // together, they produce 
    // duplicates, so it's better for us to eliminate this case so we don't 
    // have to check for duplicates during runtime if we're using a 
    // WalkingIterator.
    if(isSet(analysis, BIT_FOLLOWING | BIT_FOLLOWING_SIBLING) && 
       isSet(analysis, BIT_PRECEDING | BIT_PRECEDING_SIBLING))
      return  false;
      
    // OK, now we have to check for select="@*/axis::*" patterns, which 
    // can also cause duplicates to happen.  But select="axis*/@::*" patterns 
    // are OK, as are select="@foo/axis::*" patterns.
    // Unfortunately, we can't do this just via the analysis bits.
    
    int stepType;
    int stepCount = 0;
    boolean foundWildAttribute = false;
    
    // Steps that can traverse anything other than down a 
    // subtree or that can produce duplicates when used in 
    // combonation are counted with this variable.
    int potentialDuplicateMakingStepCount = 0;
    
    while (OpCodes.ENDOP != (stepType = compiler.getOp(stepOpCodePos)))
    {        
      stepCount++;
        
      switch (stepType)
      {
      case OpCodes.FROM_ATTRIBUTES :
      case OpCodes.MATCH_ATTRIBUTE :
        if(foundWildAttribute) // Maybe not needed, but be safe.
          return false;
        
        // This doesn't seem to work as a test for wild card.  Hmph.
        // int nodeTestType = compiler.getStepTestType(stepOpCodePos);  
        
        String localName = compiler.getStepLocalName(stepOpCodePos);
        // System.err.println("localName: "+localName);
        if(localName.equals("*"))
        {
          foundWildAttribute = true;
        }
        break;
      case OpCodes.FROM_FOLLOWING :
      case OpCodes.FROM_FOLLOWING_SIBLINGS :
      case OpCodes.FROM_PRECEDING :
      case OpCodes.FROM_PRECEDING_SIBLINGS :
      case OpCodes.FROM_PARENT :
      case OpCodes.OP_VARIABLE :
      case OpCodes.OP_EXTFUNCTION :
      case OpCodes.OP_FUNCTION :
      case OpCodes.OP_GROUP :
      case OpCodes.FROM_NAMESPACE :
      case OpCodes.FROM_ANCESTORS :
      case OpCodes.FROM_ANCESTORS_OR_SELF :      
      case OpCodes.MATCH_ANY_ANCESTOR :
      case OpCodes.MATCH_IMMEDIATE_ANCESTOR :
      case OpCodes.FROM_DESCENDANTS_OR_SELF :
      case OpCodes.FROM_DESCENDANTS :
        if(potentialDuplicateMakingStepCount > 0)
            return false;
        potentialDuplicateMakingStepCount++;
      case OpCodes.FROM_ROOT :
      case OpCodes.FROM_CHILDREN :
      case OpCodes.FROM_SELF :
        if(foundWildAttribute)
          return false;
        break;
      default :
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                                  // + stepType);
      }

      int nextStepOpCodePos = compiler.getNextStepPos(stepOpCodePos);

      if (nextStepOpCodePos < 0)
        break;
              
      stepOpCodePos = nextStepOpCodePos;
    }

    return true;
public static booleanisOneStep(int analysis)

    return (analysis & BITS_COUNT) == 0x00000001;
private static booleanisOptimizableForDescendantIterator(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos, int stepIndex)
Special purpose function to see if we can optimize the pattern for a DescendantIterator.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
param
stepIndex The top-level step index withing the iterator.
return
32 bits as an integer that give information about the location path as a whole.
throws
javax.xml.transform.TransformerException


    int stepType;
    int stepCount = 0;
    boolean foundDorDS = false;
    boolean foundSelf = false;
    boolean foundDS = false;
    
    int nodeTestType = OpCodes.NODETYPE_NODE;
    
    while (OpCodes.ENDOP != (stepType = compiler.getOp(stepOpCodePos)))
    {
      // The DescendantIterator can only do one node test.  If there's more 
      // than one, use another iterator.
      if(nodeTestType != OpCodes.NODETYPE_NODE && nodeTestType != OpCodes.NODETYPE_ROOT)
        return false;
        
      stepCount++;
      if(stepCount > 3)
        return false;
        
      boolean mightBeProximate = mightBeProximate(compiler, stepOpCodePos, stepType);
      if(mightBeProximate)
        return false;

      switch (stepType)
      {
      case OpCodes.FROM_FOLLOWING :
      case OpCodes.FROM_FOLLOWING_SIBLINGS :
      case OpCodes.FROM_PRECEDING :
      case OpCodes.FROM_PRECEDING_SIBLINGS :
      case OpCodes.FROM_PARENT :
      case OpCodes.OP_VARIABLE :
      case OpCodes.OP_EXTFUNCTION :
      case OpCodes.OP_FUNCTION :
      case OpCodes.OP_GROUP :
      case OpCodes.FROM_NAMESPACE :
      case OpCodes.FROM_ANCESTORS :
      case OpCodes.FROM_ANCESTORS_OR_SELF :
      case OpCodes.FROM_ATTRIBUTES :
      case OpCodes.MATCH_ATTRIBUTE :
      case OpCodes.MATCH_ANY_ANCESTOR :
      case OpCodes.MATCH_IMMEDIATE_ANCESTOR :
        return false;
      case OpCodes.FROM_ROOT :
        if(1 != stepCount)
          return false;
        break;
      case OpCodes.FROM_CHILDREN :
        if(!foundDS && !(foundDorDS && foundSelf))
          return false;
        break;
      case OpCodes.FROM_DESCENDANTS_OR_SELF :
        foundDS = true;
      case OpCodes.FROM_DESCENDANTS :
        if(3 == stepCount)
          return false;
        foundDorDS = true;
        break;
      case OpCodes.FROM_SELF :
        if(1 != stepCount)
          return false;
        foundSelf = true;
        break;
      default :
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, new Object[]{Integer.toString(stepType)})); //"Programmer's assertion: unknown opcode: "
                                  // + stepType);
      }
      
      nodeTestType = compiler.getStepTestType(stepOpCodePos);

      int nextStepOpCodePos = compiler.getNextStepPos(stepOpCodePos);

      if (nextStepOpCodePos < 0)
        break;
        
      if(OpCodes.ENDOP != compiler.getOp(nextStepOpCodePos))
      {
        if(compiler.countPredicates(stepOpCodePos) > 0)
        {
          return false;
        }
      }
      
      stepOpCodePos = nextStepOpCodePos;
    }

    return true;
static booleanisProximateInnerExpr(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos)

    int op = compiler.getOp(opPos);
    int innerExprOpPos = opPos+2;
    switch(op)
    {
      case OpCodes.OP_ARGUMENT:
        if(isProximateInnerExpr(compiler, innerExprOpPos))
          return true;
        break;
      case OpCodes.OP_VARIABLE:
      case OpCodes.OP_NUMBERLIT:
      case OpCodes.OP_LITERAL:
      case OpCodes.OP_LOCATIONPATH:
        break; // OK
      case OpCodes.OP_FUNCTION:
        boolean isProx = functionProximateOrContainsProximate(compiler, opPos);
        if(isProx)
          return true;
        break;
      case OpCodes.OP_GT:
      case OpCodes.OP_GTE:
      case OpCodes.OP_LT:
      case OpCodes.OP_LTE:
      case OpCodes.OP_EQUALS:
        int leftPos = compiler.getFirstChildPos(op);
        int rightPos = compiler.getNextOpPos(leftPos);
        isProx = isProximateInnerExpr(compiler, leftPos);
        if(isProx)
          return true;
        isProx = isProximateInnerExpr(compiler, rightPos);
        if(isProx)
          return true;
        break;
      default:
        return true; // be conservative...
    }
    return false;
public static booleanisSet(int analysis, int bits)

    return (0 != (analysis & bits));
public static booleanisWild(int analysis)

    return (0 != (analysis & BIT_NODETEST_ANY));
static com.sun.org.apache.xpath.internal.axes.AxesWalkerloadOneWalker(com.sun.org.apache.xpath.internal.axes.WalkingIterator lpi, com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos)
This method is for building an array of possible levels where the target element(s) could be found for a match.

param
lpi The owning location path iterator.
param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
return
non-null AxesWalker derivative.
throws
javax.xml.transform.TransformerException
xsl.usage
advanced


    AxesWalker firstWalker = null;
    int stepType = compiler.getOp(stepOpCodePos);

    if (stepType != OpCodes.ENDOP)
    {

      // m_axesWalkers = new AxesWalker[1];
      // As we unwind from the recursion, create the iterators.
      firstWalker = createDefaultWalker(compiler, stepType, lpi, 0);

      firstWalker.init(compiler, stepOpCodePos, stepType);
    }

    return firstWalker;
static com.sun.org.apache.xpath.internal.patterns.StepPatternloadSteps(com.sun.org.apache.xpath.internal.axes.MatchPatternIterator mpi, com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos, int stepIndex)
Read a LocationPath as a generalized match pattern. What this means is that the LocationPath is read backwards, as a test on a given node, to see if it matches the criteria of the selection, and ends up at the context node. Essentially, this is a backwards query from a given node, to find the context node.

So, the selection "foo/daz[2]" is, in non-abreviated expanded syntax, "self::node()/following-sibling::foo/child::daz[position()=2]". Taking this as a match pattern for a probable node, it works out to "self::daz/parent::foo[child::daz[position()=2 and isPrevStepNode()] precedingSibling::node()[isContextNodeOfLocationPath()]", adding magic isPrevStepNode and isContextNodeOfLocationPath operations. Predicates in the location path have to be executed by the following step, because they have to know the context of their execution.

param
mpi The MatchPatternIterator to which the steps will be attached.
param
compiler The compiler that holds the syntax tree/op map to construct from.
param
stepOpCodePos The current op code position within the opmap.
param
stepIndex The top-level step index withing the iterator.
return
A StepPattern object, which may contain relative StepPatterns.
throws
javax.xml.transform.TransformerException

    if (DEBUG_PATTERN_CREATION)
    {
      System.out.println("================");
      System.out.println("loadSteps for: "+compiler.getPatternString());
    }
    int stepType;
    StepPattern step = null;
    StepPattern firstStep = null, prevStep = null;
    int analysis = analyze(compiler, stepOpCodePos, stepIndex);

    while (OpCodes.ENDOP != (stepType = compiler.getOp(stepOpCodePos)))
    {
      step = createDefaultStepPattern(compiler, stepOpCodePos, mpi, analysis,
                                      firstStep, prevStep);

      if (null == firstStep)
      {
        firstStep = step;
      }
      else
      {

        //prevStep.setNextWalker(step);
        step.setRelativePathPattern(prevStep);
      }

      prevStep = step;
      stepOpCodePos = compiler.getNextStepPos(stepOpCodePos);

      if (stepOpCodePos < 0)
        break;
    }
    
    int axis = Axis.SELF;
    int paxis = Axis.SELF;
    StepPattern tail = step;
    for (StepPattern pat = step; null != pat; 
         pat = pat.getRelativePathPattern()) 
    {
      int nextAxis = pat.getAxis();
      //int nextPaxis = pat.getPredicateAxis();
      pat.setAxis(axis);
      
      // The predicate axis can't be moved!!!  Test Axes103
      // pat.setPredicateAxis(paxis);
      
      // If we have an attribute or namespace axis that went up, then 
      // it won't find the attribute in the inverse, since the select-to-match
      // axes are not invertable (an element is a parent of an attribute, but 
      // and attribute is not a child of an element).
      // If we don't do the magic below, then "@*/ancestor-or-self::*" gets
      // inverted for match to "self::*/descendant-or-self::@*/parent::node()",
      // which obviously won't work.
      // So we will rewrite this as:
      // "self::*/descendant-or-self::*/attribute::*/parent::node()"
      // Child has to be rewritten a little differently:
      // select: "@*/parent::*"
      // inverted match: "self::*/child::@*/parent::node()"
      // rewrite: "self::*/attribute::*/parent::node()"
      // Axes that go down in the select, do not have to have special treatment 
      // in the rewrite. The following inverted match will still not select 
      // anything.
      // select: "@*/child::*"
      // inverted match: "self::*/parent::@*/parent::node()"
      // Lovely business, this.
      // -sb
      int whatToShow = pat.getWhatToShow();
      if(whatToShow == DTMFilter.SHOW_ATTRIBUTE || 
         whatToShow == DTMFilter.SHOW_NAMESPACE)
      {
        int newAxis = (whatToShow == DTMFilter.SHOW_ATTRIBUTE) ? 
                       Axis.ATTRIBUTE : Axis.NAMESPACE;
        if(isDownwardAxisOfMany(axis))
        {
          StepPattern attrPat = new StepPattern(whatToShow, 
                                    pat.getNamespace(),
                                    pat.getLocalName(),
                                //newAxis, pat.getPredicateAxis);
                                                newAxis, 0); // don't care about the predicate axis
          XNumber score = pat.getStaticScore();
          pat.setNamespace(null);
          pat.setLocalName(NodeTest.WILD);
          attrPat.setPredicates(pat.getPredicates());
          pat.setPredicates(null);
          pat.setWhatToShow(DTMFilter.SHOW_ELEMENT);
          StepPattern rel = pat.getRelativePathPattern();
          pat.setRelativePathPattern(attrPat);
          attrPat.setRelativePathPattern(rel);
          attrPat.setStaticScore(score);
          
          // This is needed to inverse a following pattern, because of the 
          // wacky Xalan rules for following from an attribute.  See axes108.
          // By these rules, following from an attribute is not strictly 
          // inverseable.
          if(Axis.PRECEDING == pat.getAxis())
            pat.setAxis(Axis.PRECEDINGANDANCESTOR);
            
          else if(Axis.DESCENDANT == pat.getAxis())
            pat.setAxis(Axis.DESCENDANTORSELF);
          
          pat = attrPat;
        }
        else if(Axis.CHILD == pat.getAxis())
        {
          // In this case just change the axis.
          // pat.setWhatToShow(whatToShow);
          pat.setAxis(Axis.ATTRIBUTE);
        }
      }
      axis = nextAxis;
      //paxis = nextPaxis;
      tail = pat;
    }
    
    if(axis < Axis.ALL)
    {
      StepPattern selfPattern = new ContextMatchStepPattern(axis, paxis);
      // We need to keep the new nodetest from affecting the score...
      XNumber score = tail.getStaticScore();
      tail.setRelativePathPattern(selfPattern);
      tail.setStaticScore(score);
      selfPattern.setStaticScore(score);
    }        

    if (DEBUG_PATTERN_CREATION)
    {
      System.out.println("Done loading steps: "+step.toString());
            
      System.out.println("");
    }
    return step;  // start from last pattern?? //firstStep;
static com.sun.org.apache.xpath.internal.axes.AxesWalkerloadWalkers(com.sun.org.apache.xpath.internal.axes.WalkingIterator lpi, com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int stepOpCodePos, int stepIndex)
This method is for building an array of possible levels where the target element(s) could be found for a match.

param
lpi The owning location path iterator object.
param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
stepOpCodePos The opcode position for the step.
param
stepIndex The top-level step index withing the iterator.
return
non-null AxesWalker derivative.
throws
javax.xml.transform.TransformerException
xsl.usage
advanced


    int stepType;
    AxesWalker firstWalker = null;
    AxesWalker walker, prevWalker = null;

    int analysis = analyze(compiler, stepOpCodePos, stepIndex);

    while (OpCodes.ENDOP != (stepType = compiler.getOp(stepOpCodePos)))
    {
      walker = createDefaultWalker(compiler, stepOpCodePos, lpi, analysis);

      walker.init(compiler, stepOpCodePos, stepType);
      walker.exprSetParent(lpi);

      // walker.setAnalysis(analysis);
      if (null == firstWalker)
      {
        firstWalker = walker;
      }
      else
      {
        prevWalker.setNextWalker(walker);
        walker.setPrevWalker(prevWalker);
      }

      prevWalker = walker;
      stepOpCodePos = compiler.getNextStepPos(stepOpCodePos);

      if (stepOpCodePos < 0)
        break;
    }

    return firstWalker;
public static booleanmightBeProximate(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos, int stepType)
Tell if the predicates need to have proximity knowledge.


    boolean mightBeProximate = false;
    int argLen;

    switch (stepType)
    {
    case OpCodes.OP_VARIABLE :
    case OpCodes.OP_EXTFUNCTION :
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_GROUP :
      argLen = compiler.getArgLength(opPos);
      break;
    default :
      argLen = compiler.getArgLengthOfStep(opPos);
    }

    int predPos = compiler.getFirstPredicateOpPos(opPos);
    int count = 0;

    while (OpCodes.OP_PREDICATE == compiler.getOp(predPos))
    {
      count++;
      
      int innerExprOpPos = predPos+2;
      int predOp = compiler.getOp(innerExprOpPos);

      switch(predOp)
      {
        case OpCodes.OP_VARIABLE:
        	return true; // Would need more smarts to tell if this could be a number or not!
        case OpCodes.OP_LOCATIONPATH:
          // OK.
          break;
        case OpCodes.OP_NUMBER:
        case OpCodes.OP_NUMBERLIT:
          return true; // that's all she wrote!
        case OpCodes.OP_FUNCTION:
          boolean isProx 
            = functionProximateOrContainsProximate(compiler, innerExprOpPos);
          if(isProx)
            return true;
          break;
        case OpCodes.OP_GT:
        case OpCodes.OP_GTE:
        case OpCodes.OP_LT:
        case OpCodes.OP_LTE:
        case OpCodes.OP_EQUALS:
          int leftPos = compiler.getFirstChildPos(innerExprOpPos);
          int rightPos = compiler.getNextOpPos(leftPos);
          isProx = isProximateInnerExpr(compiler, leftPos);
          if(isProx)
            return true;
          isProx = isProximateInnerExpr(compiler, rightPos);
          if(isProx)
            return true;
          break;
        default:
          return true; // be conservative...
      }

      predPos = compiler.getNextOpPos(predPos);
    }

    return mightBeProximate;
public static com.sun.org.apache.xml.internal.dtm.DTMIteratornewDTMIterator(com.sun.org.apache.xpath.internal.compiler.Compiler compiler, int opPos, boolean isTopLevel)
Create a new LocPathIterator iterator. The exact type of iterator returned is based on an analysis of the XPath operations.

param
compiler non-null reference to compiler object that has processed the XPath operations into an opcode map.
param
opPos The position of the operation code for this itterator.
return
non-null reference to a LocPathIterator or derivative.
throws
javax.xml.transform.TransformerException


    int firstStepPos = compiler.getFirstChildPos(opPos);
    int analysis = analyze(compiler, firstStepPos, 0);
    boolean isOneStep = isOneStep(analysis);
    DTMIterator iter;

    // Is the iteration a one-step attribute pattern (i.e. select="@foo")?
    if (isOneStep && walksSelfOnly(analysis) && 
        isWild(analysis) && !hasPredicate(analysis))
    {
      if (DEBUG_ITERATOR_CREATION)
        diagnoseIterator("SelfIteratorNoPredicate", analysis, compiler);

      // Then use a simple iteration of the attributes, with node test 
      // and predicate testing.
      iter = new SelfIteratorNoPredicate(compiler, opPos, analysis);
    }
    // Is the iteration exactly one child step?
    else if (walksChildrenOnly(analysis) && isOneStep)
    {

      // Does the pattern specify *any* child with no predicate? (i.e. select="child::node()".
      if (isWild(analysis) && !hasPredicate(analysis))
      {
        if (DEBUG_ITERATOR_CREATION)
          diagnoseIterator("ChildIterator", analysis, compiler);

        // Use simple child iteration without any test.
        iter = new ChildIterator(compiler, opPos, analysis);
      }
      else
      {
        if (DEBUG_ITERATOR_CREATION)
          diagnoseIterator("ChildTestIterator", analysis, compiler);

        // Else use simple node test iteration with predicate test.
        iter = new ChildTestIterator(compiler, opPos, analysis);
      }
    }
    // Is the iteration a one-step attribute pattern (i.e. select="@foo")?
    else if (isOneStep && walksAttributes(analysis))
    {
      if (DEBUG_ITERATOR_CREATION)
        diagnoseIterator("AttributeIterator", analysis, compiler);

      // Then use a simple iteration of the attributes, with node test 
      // and predicate testing.
      iter = new AttributeIterator(compiler, opPos, analysis);
    }
    else if(isOneStep && !walksFilteredList(analysis))
    {
      if( !walksNamespaces(analysis) 
      && (walksInDocOrder(analysis) || isSet(analysis, BIT_PARENT)))
      {
        if (false || DEBUG_ITERATOR_CREATION)
          diagnoseIterator("OneStepIteratorForward", analysis, compiler);
  
        // Then use a simple iteration of the attributes, with node test 
        // and predicate testing.
        iter = new OneStepIteratorForward(compiler, opPos, analysis);
      }
      else
      {
        if (false || DEBUG_ITERATOR_CREATION)
          diagnoseIterator("OneStepIterator", analysis, compiler);
  
        // Then use a simple iteration of the attributes, with node test 
        // and predicate testing.
        iter = new OneStepIterator(compiler, opPos, analysis);
      }
    }

    // Analysis of "//center":
    // bits: 1001000000001010000000000000011
    // count: 3
    // root
    // child:node()
    // BIT_DESCENDANT_OR_SELF
    // It's highly possible that we should have a seperate bit set for 
    // "//foo" patterns.
    // For at least the time being, we can't optimize patterns like 
    // "//table[3]", because this has to be analyzed as 
    // "/descendant-or-self::node()/table[3]" in order for the indexes 
    // to work right.
    else if (isOptimizableForDescendantIterator(compiler, firstStepPos, 0)
              // && getStepCount(analysis) <= 3 
              // && walksDescendants(analysis) 
              // && walksSubtreeOnlyFromRootOrContext(analysis)
             )
    {
      if (DEBUG_ITERATOR_CREATION)
        diagnoseIterator("DescendantIterator", analysis, compiler);

      iter = new DescendantIterator(compiler, opPos, analysis);
    }
    else
    { 
      if(isNaturalDocOrder(compiler, firstStepPos, 0, analysis))
      {
        if (false || DEBUG_ITERATOR_CREATION)
        {
          diagnoseIterator("WalkingIterator", analysis, compiler);
        }
  
        iter = new WalkingIterator(compiler, opPos, analysis, true);
      }
      else
      {
//        if (DEBUG_ITERATOR_CREATION)
//          diagnoseIterator("MatchPatternIterator", analysis, compiler);
//
//        return new MatchPatternIterator(compiler, opPos, analysis);
        if (DEBUG_ITERATOR_CREATION)
          diagnoseIterator("WalkingIteratorSorted", analysis, compiler);

        iter = new WalkingIteratorSorted(compiler, opPos, analysis, true);
      }
    }
    if(iter instanceof LocPathIterator)
      ((LocPathIterator)iter).setIsTopLevel(isTopLevel);
      
    return iter;
public static booleanwalksAncestors(int analysis)

    return isSet(analysis, BIT_ANCESTOR | BIT_ANCESTOR_OR_SELF);
public static booleanwalksAttributes(int analysis)

    return (0 != (analysis & BIT_ATTRIBUTE));
public static booleanwalksChildren(int analysis)

    return (0 != (analysis & BIT_CHILD));
public static booleanwalksChildrenAndExtraAndSelfOnly(int analysis)

    return walksChildren(analysis)
           && !walksDescendants(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && (!isAbsolute(analysis) || isSet(analysis, BIT_ROOT))
           ;
public static booleanwalksChildrenOnly(int analysis)

    return walksChildren(analysis)
           && !isSet(analysis, BIT_SELF)
           && !walksExtraNodes(analysis)
           && !walksDescendants(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && (!isAbsolute(analysis) || isSet(analysis, BIT_ROOT))
           ;
public static booleanwalksDescendants(int analysis)

    return isSet(analysis, BIT_DESCENDANT | BIT_DESCENDANT_OR_SELF);
public static booleanwalksDescendantsAndExtraAndSelfOnly(int analysis)

    return !walksChildren(analysis)
           && walksDescendants(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && (!isAbsolute(analysis) || isSet(analysis, BIT_ROOT))
           ;
public static booleanwalksDownExtraOnly(int analysis)

    return walksSubtree(analysis) &&  walksExtraNodes(analysis)
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isAbsolute(analysis) 
           ;
public static booleanwalksDownOnly(int analysis)

    return walksSubtree(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isAbsolute(analysis) 
           ;
public static booleanwalksExtraNodes(int analysis)

    return isSet(analysis, BIT_NAMESPACE | BIT_ATTRIBUTE);
public static booleanwalksExtraNodesOnly(int analysis)

    return walksExtraNodes(analysis)
           && !isSet(analysis, BIT_SELF) 
           && !walksSubtree(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isAbsolute(analysis) 
           ;
public static booleanwalksFilteredList(int analysis)

    return isSet(analysis, BIT_FILTER);
public static booleanwalksFollowingOnlyMaybeAbsolute(int analysis)

    return isSet(analysis, BIT_SELF | BIT_FOLLOWING_SIBLING | BIT_FOLLOWING)
           && !walksSubtree(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           ;
public static booleanwalksInDocOrder(int analysis)

    return (walksSubtreeOnlyMaybeAbsolute(analysis)
           || walksExtraNodesOnly(analysis)
           || walksFollowingOnlyMaybeAbsolute(analysis)) 
           && !isSet(analysis, BIT_FILTER) 
           ;
public static booleanwalksNamespaces(int analysis)

    return (0 != (analysis & BIT_NAMESPACE));
public static booleanwalksSelfOnly(int analysis)

    return isSet(analysis, BIT_SELF) 
           && !walksSubtree(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isAbsolute(analysis) 
           ;
public static booleanwalksSideways(int analysis)

    return isSet(analysis, BIT_FOLLOWING | BIT_FOLLOWING_SIBLING | 
                           BIT_PRECEDING | BIT_PRECEDING_SIBLING);
public static booleanwalksSubtree(int analysis)

    return isSet(analysis, BIT_DESCENDANT | BIT_DESCENDANT_OR_SELF | BIT_CHILD);
public static booleanwalksSubtreeOnly(int analysis)

    return walksSubtreeOnlyMaybeAbsolute(analysis) 
           && !isAbsolute(analysis) 
           ;
public static booleanwalksSubtreeOnlyFromRootOrContext(int analysis)

    return walksSubtree(analysis)
           && !walksExtraNodes(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isSet(analysis, BIT_FILTER) 
           ;
public static booleanwalksSubtreeOnlyMaybeAbsolute(int analysis)

    return walksSubtree(analysis)
           && !walksExtraNodes(analysis) 
           && !walksUp(analysis) 
           && !walksSideways(analysis) 
           ;
public static booleanwalksUp(int analysis)

    return isSet(analysis, BIT_PARENT | BIT_ANCESTOR | BIT_ANCESTOR_OR_SELF);
public static booleanwalksUpOnly(int analysis)

    return !walksSubtree(analysis) 
           && walksUp(analysis) 
           && !walksSideways(analysis) 
           && !isAbsolute(analysis) 
           ;