/* ==================================================================== | |
Licensed to the Apache Software Foundation (ASF) under one or more | |
contributor license agreements. See the NOTICE file distributed with | |
this work for additional information regarding copyright ownership. | |
The ASF licenses this file to You under the Apache License, Version 2.0 | |
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Unless required by applicable law or agreed to in writing, software | |
distributed under the License is distributed on an "AS IS" BASIS, | |
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package org.apache.poi.ss.formula.functions; | |
import org.apache.poi.ss.formula.OperationEvaluationContext; | |
import org.apache.poi.ss.formula.eval.*; | |
import java.math.BigInteger; | |
import java.util.HashMap; | |
/** | |
* Implementation for Excel FACTDOUBLE() function.<p/> | |
* <p/> | |
* <b>Syntax</b>:<br/> <b>FACTDOUBLE </b>(<b>number</b>)<br/> | |
* <p/> | |
* Returns the double factorial of a number. | |
* <p/> | |
* Number is the value for which to return the double factorial. If number is not an integer, it is truncated. | |
* <p/> | |
* Remarks | |
* <ul> | |
* <li>If number is nonnumeric, FACTDOUBLE returns the #VALUE! error value.</li> | |
* <li>If number is negative, FACTDOUBLE returns the #NUM! error value.</li> | |
* </ul> | |
* Use a cache for more speed of previously calculated factorial | |
* | |
* @author cedric dot walter @ gmail dot com | |
*/ | |
public class FactDouble extends Fixed1ArgFunction implements FreeRefFunction { | |
public static final FreeRefFunction instance = new FactDouble(); | |
//Caching of previously calculated factorial for speed | |
static HashMap<Integer, BigInteger> cache = new HashMap<Integer, BigInteger>(); | |
public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval numberVE) { | |
int number; | |
try { | |
number = OperandResolver.coerceValueToInt(numberVE); | |
} catch (EvaluationException e) { | |
return ErrorEval.VALUE_INVALID; | |
} | |
if (number < 0) { | |
return ErrorEval.NUM_ERROR; | |
} | |
return new NumberEval(factorial(number).longValue()); | |
} | |
public static BigInteger factorial(int n) { | |
if (n == 0 || n < 0) { | |
return BigInteger.ONE; | |
} | |
if (cache.containsKey(n)) { | |
return cache.get(n); | |
} | |
BigInteger result = BigInteger.valueOf(n).multiply(factorial(n - 2)); | |
cache.put(n, result); | |
return result; | |
} | |
public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) { | |
if (args.length != 1) { | |
return ErrorEval.VALUE_INVALID; | |
} | |
return evaluate(ec.getRowIndex(), ec.getColumnIndex(), args[0]); | |
} | |
} |