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package java_cup;
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import java.util.BitSet;
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/** A set of terminals implemented as a bitset.
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* @version last updated: 11/25/95
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* @author Scott Hudson
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*/
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public class terminal_set {
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/*-----------------------------------------------------------*/
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/*--- Constructor(s) ----------------------------------------*/
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/*-----------------------------------------------------------*/
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/** Constructor for an empty set. */
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public terminal_set()
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{
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/* allocate the bitset at what is probably the right size */
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_elements = new BitSet(terminal.number());
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Constructor for cloning from another set.
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* @param other the set we are cloning from.
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*/
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public terminal_set(terminal_set other)
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throws internal_error
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{
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not_null(other);
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_elements = (BitSet)other._elements.clone();
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};
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/*-----------------------------------------------------------*/
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/*--- (Access to) Static (Class) Variables ------------------*/
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/*-----------------------------------------------------------*/
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/** Constant for the empty set. */
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public static final terminal_set EMPTY = new terminal_set();
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/*-----------------------------------------------------------*/
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/*--- (Access to) Instance Variables ------------------------*/
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/*-----------------------------------------------------------*/
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/** Bitset to implement the actual set. */
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protected BitSet _elements;
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/*-----------------------------------------------------------*/
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/*--- General Methods ----------------------------------------*/
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/*-----------------------------------------------------------*/
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/** Helper function to test for a null object and throw an exception if
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* one is found.
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* @param obj the object we are testing.
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*/
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protected void not_null(Object obj) throws internal_error
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{
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if (obj == null)
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throw new internal_error("Null object used in set operation");
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Determine if the set is empty. */
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public boolean empty()
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{
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return equals(EMPTY);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Determine if the set contains a particular terminal.
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* @param sym the terminal symbol we are looking for.
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*/
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public boolean contains(terminal sym)
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throws internal_error
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{
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not_null(sym);
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return _elements.get(sym.index());
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Given its index determine if the set contains a particular terminal.
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* @param indx the index of the terminal in question.
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*/
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public boolean contains(int indx)
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{
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return _elements.get(indx);
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Determine if this set is an (improper) subset of another.
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* @param other the set we are testing against.
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*/
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public boolean is_subset_of(terminal_set other)
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throws internal_error
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{
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not_null(other);
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/* make a copy of the other set */
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BitSet copy_other = (BitSet)other._elements.clone();
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/* and or in */
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copy_other.or(_elements);
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/* if it hasn't changed, we were a subset */
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return copy_other.equals(other._elements);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Determine if this set is an (improper) superset of another.
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* @param other the set we are testing against.
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*/
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public boolean is_superset_of(terminal_set other)
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throws internal_error
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{
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not_null(other);
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return other.is_subset_of(this);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Add a single terminal to the set.
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* @param sym the terminal being added.
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* @return true if this changes the set.
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*/
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public boolean add(terminal sym)
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throws internal_error
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{
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boolean result;
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not_null(sym);
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/* see if we already have this */
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result = _elements.get(sym.index());
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/* if not we add it */
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if (!result)
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_elements.set(sym.index());
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return result;
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Remove a terminal if it is in the set.
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* @param sym the terminal being removed.
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*/
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public void remove(terminal sym)
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throws internal_error
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{
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not_null(sym);
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_elements.clear(sym.index());
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Add (union) in a complete set.
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* @param other the set being added.
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* @return true if this changes the set.
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*/
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public boolean add(terminal_set other)
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throws internal_error
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{
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not_null(other);
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/* make a copy */
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BitSet copy = (BitSet)_elements.clone();
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/* or in the other set */
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_elements.or(other._elements);
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/* changed if we are not the same as the copy */
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return !_elements.equals(copy);
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};
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Determine if this set intersects another.
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* @param other the other set in question.
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*/
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public boolean intersects(terminal_set other)
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throws internal_error
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{
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not_null(other);
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/* make a copy of the other set */
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BitSet copy = (BitSet)other._elements.clone();
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/* xor out our values */
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copy.xor(this._elements);
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/* see if its different */
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return !copy.equals(other._elements);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Equality comparison. */
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public boolean equals(terminal_set other)
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{
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if (other == null)
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return false;
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else
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return _elements.equals(other._elements);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Generic equality comparison. */
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public boolean equals(Object other)
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{
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if (!(other instanceof terminal_set))
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return false;
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else
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return equals((terminal_set)other);
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}
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/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
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/** Convert to string. */
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public String toString()
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{
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String result;
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boolean comma_flag;
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result = "{";
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comma_flag = false;
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for (int t = 0; t < terminal.number(); t++)
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{
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if (_elements.get(t))
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{
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if (comma_flag)
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result += ", ";
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else
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comma_flag = true;
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result += terminal.find(t).name();
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}
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}
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result += "}";
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return result;
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}
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/*-----------------------------------------------------------*/
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};
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