This has been changed from the previous incarnations of this * class to be fairly low level.
*/ public final class VariableStack implements Cloneable { /** * Constructor for a variable stack. */ public VariableStack() { reset(); } /** * Returns a clone of this variable stack. * * @return a clone of this variable stack. * * @throws CloneNotSupportedException */ public synchronized Object clone() throws CloneNotSupportedException { VariableStack vs = (VariableStack) super.clone(); // I *think* I can get away with a shallow clone here? vs._sf = (XObject[]) _sf.clone(); vs._links = (int[]) _links.clone(); return vs; } /** * The stack frame where all variables and params will be kept. * @serial */ XObject[] _sf = new XObject[XPathContext.RECURSIONLIMIT * 2]; /** * The top of the stack frame (_sf).
* @serial
*/
int _top;
/**
* The bottom index of the current frame (relative to _sf).
* @serial
*/
private int _cfb;
/**
* The stack of frame positions. I call 'em links because of distant
*
* Motorola 68000 assembler memories. :-)
* @serial
*/
int[] _links = new int[XPathContext.RECURSIONLIMIT];
/**
* The top of the links stack.
*/
int _linksTop;
/**
* Get the element at the given index, regardless of stackframe.
*
* @param i index from zero.
*
* @return The item at the given index.
*/
public final XObject elementAt(final int i)
{
return _sf[i];
}
/**
* Get size of the stack.
*
* @return the total size of the execution stack.
*/
public final int size()
{
return _top;
}
/**
* Reset the stack to a start position.
*
* @return the total size of the execution stack.
*/
public final void reset()
{
_top = 0;
_linksTop = 0;
// Adding one here to the stack of frame positions will allow us always
// to look one under without having to check if we're at zero.
// (As long as the caller doesn't screw up link/unlink.)
_links[_linksTop++] = 0;
}
/**
* Set the current stack frame.
*
* @param sf The new stack frame position.
*/
public final void setStackFrame(int sf)
{
_cfb = sf;
}
/**
* Get the position from where the search should start,
* which is either the searchStart property, or the top
* of the stack if that value is -1.
*
* @return The current stack frame position.
*/
public final int getStackFrame()
{
return _cfb;
}
/**
* Allocates memory (called a stackframe) on the stack; used to store
* local variables and parameter arguments.
*
* I use the link/unlink concept because of distant * * Motorola 68000 assembler memories.
* * @param size The size of the stack frame allocation. This ammount should * normally be the maximum number of variables that you can have allocated * at one time in the new stack frame. * * @return The bottom of the stack frame, from where local variable addressing * should start from. */ public final int link(final int size) { _cfb = _top; _top += size; if (_top >= _sf.length) { XObject newsf[] = new XObject[_sf.length + (1024 * 4) + size]; System.arraycopy(_sf, 0, newsf, 0, _sf.length); _sf = newsf; } if (_linksTop+1 >= _links.length) { int newlinks[] = new int[_links.length + (1024 * 2)]; System.arraycopy(_links, 0, newlinks, 0, _links.length); _links = newlinks; } _links[_linksTop++] = _cfb; return _cfb; } /** * Free up the stack frame that was last allocated with * {@link link(int size)}. */ public final void unlink() { _top = _links[--_linksTop]; _cfb = _links[_linksTop - 1]; } /** * Set a local variable or parameter in the current stack frame. * * * @param index Local variable index relative to the current stack * frame bottom. * * @param val The value of the variable that is being set. */ public final void setLocalVariable(int index, XObject val) { _sf[index+_cfb] = val; } /** * Set a local variable or parameter in the specified stack frame. * * * @param index Local variable index relative to the current stack * frame bottom. * * @param val The value of the variable that is being set. */ public final void setLocalVariable(int index, XObject val, int stackFrame) { _sf[index+stackFrame] = val; } /** * Get a local variable or parameter in the current stack frame. * * * @param xctxt The XPath context, which must be passed in order to * lazy evaluate variables. * * @param index Local variable index relative to the current stack * frame bottom. * * @return The value of the variable. * * @throws TransformerException */ public final XObject getLocalVariable(XPathContext xctxt, int index) throws TransformerException { index += _cfb; XObject val = _sf[index]; // Lazy execution of variables. if (val.getType() == XObject.CLASS_UNRESOLVEDVARIABLE) return (_sf[index] = val.execute(xctxt)); return val; } /** * Get a local variable or parameter in the current stack frame. * * * @param index Local variable index relative to the given * frame bottom. * * @return The value of the variable. * * @throws TransformerException */ public final XObject getLocalVariable(int index, int frame) throws TransformerException { index += frame; XObject val = _sf[index]; return val; } /** * Tell if a local variable has been set or not. * * @param index Local variable index relative to the current stack * frame bottom. * * @return true if the value at the index is not null. * * @throws TransformerException */ public final boolean isLocalSet(int index) throws TransformerException { return (_sf[index + _cfb] != null); } private static XObject[] m_nulls = new XObject[1024]; /** * Use this to clear the variables in a section of the stack. This is * used to clear the parameter section of the stack, so that default param * values can tell if they've already been set. It is important to note that * this function has a 1K limitation. * * @param start The start position, relative to the current local stack frame. * @param len The number of slots to be cleared. */ public final void clearLocalSlots(int start, int len) { start+=_cfb; System.arraycopy(m_nulls, 0, _sf, start, len); } /** * Set a global variable or parameter in the global stack frame. * * * @param index Local variable index relative to the global stack frame * bottom. * * @param val The value of the variable that is being set. */ public final void setGlobalVariable(final int index, final XObject val) { _sf[index] = val; } /** * Get a global variable or parameter from the global stack frame. * * * @param xctxt The XPath context, which must be passed in order to * lazy evaluate variables. * * @param index Global variable index relative to the global stack * frame bottom. * * @return The value of the variable. * * @throws TransformerException */ public final XObject getGlobalVariable(XPathContext xctxt, final int index) throws TransformerException { XObject val = _sf[index]; // Lazy execution of variables. if (val.getType() == XObject.CLASS_UNRESOLVEDVARIABLE) return (_sf[index] = val.execute(xctxt)); return val; } } // end VariableStack