/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 2005 Dave Brosius <dbrosius@users.sourceforge.net>
 * Copyright (C) 2005 University of Maryland
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.detect;

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

import org.apache.bcel.classfile.Code;
import org.apache.bcel.classfile.Constant;
import org.apache.bcel.classfile.ConstantDouble;
import org.apache.bcel.classfile.ConstantFloat;
import org.apache.bcel.classfile.ConstantLong;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.StatelessDetector;

/**
 * Find occurrences of Math using constants, where the result of the calculation
 * can be determined statically. Replacing the math formula with the constant
 * performs better, and sometimes is more accurate.
 * 
 * @author Dave Brosius
 */
public class UnnecessaryMath extends BytecodeScanningDetector implements StatelessDetector {
    static final int SEEN_NOTHING = 0;

    static final int SEEN_DCONST = 1;

    private BugReporter bugReporter;

    private int state = SEEN_NOTHING;

    private double constValue;

    private static final Set<String> zeroMethods = new HashSet<String>() {
        {
            add("acos");
            add("asin");
            add("atan");
            add("atan2");
            add("cbrt");
            add("cos");
            add("cosh");
            add("exp");
            add("expm1");
            add("log");
            add("log10");
            add("pow");
            add("sin");
            add("sinh");
            add("sqrt");
            add("tan");
            add("tanh");
            add("toDegrees");
            add("toRadians");
        }
    };

    private static final Set<String> oneMethods = new HashSet<String>() {
        {
            add("acos");
            add("asin");
            add("atan");
            add("cbrt");
            add("exp");
            add("log");
            add("log10");
            add("pow");
            add("sqrt");
            add("toDegrees");
        }
    };

    private static final Set<String> anyMethods = new HashSet<String>() {
        {
            add("abs");
            add("ceil");
            add("floor");
            add("rint");
            add("round");
        }
    };

    public UnnecessaryMath(BugReporter bugReporter) {
        this.bugReporter = bugReporter;
    }

    @Override
    public void visit(Code obj) {
        // Don't complain about unnecessary math calls in class initializers,
        // since they may be there to improve readability.
        if (getMethod().getName().equals("<clinit>"))
            return;

        state = SEEN_NOTHING;
        super.visit(obj);
    }

    @Override
    public void sawOpcode(int seen) {
        if (state == SEEN_NOTHING) {
            if ((seen == DCONST_0) || (seen == DCONST_1)) {
                constValue = seen - DCONST_0;
                state = SEEN_DCONST;
            } else if ((seen == LDC2_W) || (seen == LDC_W)) {
                state = SEEN_DCONST;
                Constant c = this.getConstantRefOperand();
                if (c instanceof ConstantDouble)
                    constValue = ((ConstantDouble) c).getBytes();
                else if (c instanceof ConstantFloat)
                    constValue = ((ConstantFloat) c).getBytes();
                else if (c instanceof ConstantLong)
                    constValue = ((ConstantLong) c).getBytes();
                else
                    state = SEEN_NOTHING;
            }
        } else if (state == SEEN_DCONST) {
            if (seen == INVOKESTATIC) {
                state = SEEN_NOTHING;
                if (getDottedClassConstantOperand().equals("java.lang.Math")) {
                    String methodName = getNameConstantOperand();

                    if (((constValue == 0.0) && zeroMethods.contains(methodName))
                            || ((constValue == 1.0) && oneMethods.contains(methodName)) || (anyMethods.contains(methodName))) {
                        bugReporter.reportBug(new BugInstance(this, "UM_UNNECESSARY_MATH", LOW_PRIORITY).addClassAndMethod(this)
                                .addSourceLine(this));
                    }
                }
            }
            state = SEEN_NOTHING;
        }
    }
}

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