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Statistical sampling library for use in virtdata libraries, based on apache commons math 4

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/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.runtime.atn;

import org.antlr.v4.runtime.RuleContext;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.misc.IntervalSet;

import java.util.BitSet;
import java.util.HashSet;
import java.util.Set;

public class LL1Analyzer {
	/** Special value added to the lookahead sets to indicate that we hit
	 *  a predicate during analysis if {@code seeThruPreds==false}.
	 */
	public static final int HIT_PRED = Token.INVALID_TYPE;

	public final ATN atn;

	public LL1Analyzer(ATN atn) { this.atn = atn; }

	/**
	 * Calculates the SLL(1) expected lookahead set for each outgoing transition
	 * of an {@link ATNState}. The returned array has one element for each
	 * outgoing transition in {@code s}. If the closure from transition
	 * i leads to a semantic predicate before matching a symbol, the
	 * element at index i of the result will be {@code null}.
	 *
	 * @param s the ATN state
	 * @return the expected symbols for each outgoing transition of {@code s}.
	 */
	public IntervalSet[] getDecisionLookahead(ATNState s) {
//		System.out.println("LOOK("+s.stateNumber+")");
		if ( s==null ) {
			return null;
		}

		IntervalSet[] look = new IntervalSet[s.getNumberOfTransitions()];
		for (int alt = 0; alt < s.getNumberOfTransitions(); alt++) {
			look[alt] = new IntervalSet();
			Set lookBusy = new HashSet();
			boolean seeThruPreds = false; // fail to get lookahead upon pred
			_LOOK(s.transition(alt).target, null, PredictionContext.EMPTY,
				  look[alt], lookBusy, new BitSet(), seeThruPreds, false);
			// Wipe out lookahead for this alternative if we found nothing
			// or we had a predicate when we !seeThruPreds
			if ( look[alt].size()==0 || look[alt].contains(HIT_PRED) ) {
				look[alt] = null;
			}
		}
		return look;
	}

	/**
	 * Compute set of tokens that can follow {@code s} in the ATN in the
	 * specified {@code ctx}.
	 *
	 * 

If {@code ctx} is {@code null} and the end of the rule containing * {@code s} is reached, {@link Token#EPSILON} is added to the result set. * If {@code ctx} is not {@code null} and the end of the outermost rule is * reached, {@link Token#EOF} is added to the result set.

* * @param s the ATN state * @param ctx the complete parser context, or {@code null} if the context * should be ignored * * @return The set of tokens that can follow {@code s} in the ATN in the * specified {@code ctx}. */ public IntervalSet LOOK(ATNState s, RuleContext ctx) { return LOOK(s, null, ctx); } /** * Compute set of tokens that can follow {@code s} in the ATN in the * specified {@code ctx}. * *

If {@code ctx} is {@code null} and the end of the rule containing * {@code s} is reached, {@link Token#EPSILON} is added to the result set. * If {@code ctx} is not {@code null} and the end of the outermost rule is * reached, {@link Token#EOF} is added to the result set.

* * @param s the ATN state * @param stopState the ATN state to stop at. This can be a * {@link BlockEndState} to detect epsilon paths through a closure. * @param ctx the complete parser context, or {@code null} if the context * should be ignored * * @return The set of tokens that can follow {@code s} in the ATN in the * specified {@code ctx}. */ public IntervalSet LOOK(ATNState s, ATNState stopState, RuleContext ctx) { IntervalSet r = new IntervalSet(); boolean seeThruPreds = true; // ignore preds; get all lookahead PredictionContext lookContext = ctx != null ? PredictionContext.fromRuleContext(s.atn, ctx) : null; _LOOK(s, stopState, lookContext, r, new HashSet(), new BitSet(), seeThruPreds, true); return r; } /** * Compute set of tokens that can follow {@code s} in the ATN in the * specified {@code ctx}. * *

If {@code ctx} is {@code null} and {@code stopState} or the end of the * rule containing {@code s} is reached, {@link Token#EPSILON} is added to * the result set. If {@code ctx} is not {@code null} and {@code addEOF} is * {@code true} and {@code stopState} or the end of the outermost rule is * reached, {@link Token#EOF} is added to the result set.

* * @param s the ATN state. * @param stopState the ATN state to stop at. This can be a * {@link BlockEndState} to detect epsilon paths through a closure. * @param ctx The outer context, or {@code null} if the outer context should * not be used. * @param look The result lookahead set. * @param lookBusy A set used for preventing epsilon closures in the ATN * from causing a stack overflow. Outside code should pass * {@code new HashSet} for this argument. * @param calledRuleStack A set used for preventing left recursion in the * ATN from causing a stack overflow. Outside code should pass * {@code new BitSet()} for this argument. * @param seeThruPreds {@code true} to true semantic predicates as * implicitly {@code true} and "see through them", otherwise {@code false} * to treat semantic predicates as opaque and add {@link #HIT_PRED} to the * result if one is encountered. * @param addEOF Add {@link Token#EOF} to the result if the end of the * outermost context is reached. This parameter has no effect if {@code ctx} * is {@code null}. */ protected void _LOOK(ATNState s, ATNState stopState, PredictionContext ctx, IntervalSet look, Set lookBusy, BitSet calledRuleStack, boolean seeThruPreds, boolean addEOF) { // System.out.println("_LOOK("+s.stateNumber+", ctx="+ctx); ATNConfig c = new ATNConfig(s, 0, ctx); if ( !lookBusy.add(c) ) return; if (s == stopState) { if (ctx == null) { look.add(Token.EPSILON); return; } else if (ctx.isEmpty() && addEOF) { look.add(Token.EOF); return; } } if ( s instanceof RuleStopState ) { if ( ctx==null ) { look.add(Token.EPSILON); return; } else if (ctx.isEmpty() && addEOF) { look.add(Token.EOF); return; } if ( ctx != PredictionContext.EMPTY ) { // run thru all possible stack tops in ctx boolean removed = calledRuleStack.get(s.ruleIndex); try { calledRuleStack.clear(s.ruleIndex); for (int i = 0; i < ctx.size(); i++) { ATNState returnState = atn.states.get(ctx.getReturnState(i)); // System.out.println("popping back to "+retState); _LOOK(returnState, stopState, ctx.getParent(i), look, lookBusy, calledRuleStack, seeThruPreds, addEOF); } } finally { if (removed) { calledRuleStack.set(s.ruleIndex); } } return; } } int n = s.getNumberOfTransitions(); for (int i=0; i




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