AppsheetEpplus/FormulaParsing/Excel/Functions/Math/Rounddown.cs

/* Copyright (C) 2011  Jan Källman
 *
 * 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.
 *
 * The GNU Lesser General Public License can be viewed at http://www.opensource.org/licenses/lgpl-license.php
 * If you unfamiliar with this license or have questions about it, here is an http://www.gnu.org/licenses/gpl-faq.html
 *
 * All code and executables are provided "as is" with no warranty either express or implied.
 * The author accepts no liability for any damage or loss of business that this product may cause.
 *
 * Code change notes:
 *
 * Author							Change						Date
 *******************************************************************************
 * Mats Alm   		                Added		                2014-01-06
 *******************************************************************************/

using System.Collections.Generic;

namespace AppsheetEpplus;

public class Rounddown : ExcelFunction {
  public override CompileResult Execute(
      IEnumerable<FunctionArgument> arguments,
      ParsingContext context) {
    ValidateArguments(arguments, 2);
    var number = ArgToDecimal(arguments, 0);
    var nDecimals = ArgToInt(arguments, 1);

    var nFactor = number < 0 ? -1 : 1;
    number *= nFactor;

    double result;
    if (nDecimals > 0) {
      result = RoundDownDecimalNumber(number, nDecimals);
    } else {
      result = (int)System.Math.Floor(number);
      result = result - (result % System.Math.Pow(10, (nDecimals * -1)));
    }
    return CreateResult(result * nFactor, DataType.Decimal);
  }

  private static double RoundDownDecimalNumber(double number, int nDecimals) {
    var integerPart = System.Math.Floor(number);
    var decimalPart = number - integerPart;
    decimalPart = System.Math.Pow(10d, nDecimals) * decimalPart;
    decimalPart = System.Math.Truncate(decimalPart) / System.Math.Pow(10d, nDecimals);
    var result = integerPart + decimalPart;
    return result;
  }
}