BN089-BS开发框架MVC4版/source20131023/Zephyr.Net/Zephyr.Utils/Document/Excel/NPOI/SS/Util/NumberComparer.cs

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using System;
using System.Collections.Generic;
using System.Text;
using Zephyr.Utils.NPOI.Util;

namespace Zephyr.Utils.NPOI.SS.Util
{
    public class NumberComparer
    {
        /**
         * This class attempts to reproduce Excel's behaviour for comparing numbers.  Results are
         * mostly the same as those from {@link Double#compare(double, double)} but with some
         * rounding.  For numbers that are very close, this code converts to a format having 15
         * decimal digits of precision and a decimal exponent, before completing the comparison.
         * <p/>
         * In Excel formula evaluation, expressions like "(0.06-0.01)=0.05" evaluate to "TRUE" even
         * though the equivalent java expression is <c>false</c>.  In examples like this,
         * Excel achieves the effect by having additional logic for comparison operations.
         * <p/>
         * <p/>
         * Note - Excel also gives special treatment to expressions like "0.06-0.01-0.05" which
         * evaluates to "0" (in java, rounding anomalies give a result of 6.9E-18).  The special
         * behaviour here is for different reasons to the example above:  If the last operator in a
         * cell formula is '+' or '-' and the result is less than 2<sup>50</sup> times smaller than
         * first operand, the result is rounded to zero.
         * Needless to say, the two rules are not consistent and it is relatively easy to find
         * examples that satisfy<br/>
         * "A=B" is "TRUE" but "A-B" is not "0"<br/>
         * and<br/>
         * "A=B" is "FALSE" but "A-B" is "0"<br/>
         * <br/>
         * This rule (for rounding the result of a final addition or subtraction), has not been
         * implemented in POI (as of Jul-2009).
         *
         * @return <code>negative, 0, or positive</code> according to the standard Excel comparison
         * of values <c>a</c> and <c>b</c>.
         */
        public static int Compare(double a, double b)
        {
            long rawBitsA = BitConverter.DoubleToInt64Bits(a);
            long rawBitsB = BitConverter.DoubleToInt64Bits(b);

            int biasedExponentA = IEEEDouble.GetBiasedExponent(rawBitsA);
            int biasedExponentB = IEEEDouble.GetBiasedExponent(rawBitsB);

            if (biasedExponentA == IEEEDouble.BIASED_EXPONENT_SPECIAL_VALUE)
            {
                throw new ArgumentException("Special double values are not allowed: " + ToHex(a));
            }
            if (biasedExponentB == IEEEDouble.BIASED_EXPONENT_SPECIAL_VALUE)
            {
                throw new ArgumentException("Special double values are not allowed: " + ToHex(a));
            }

            int cmp;

            // sign bit is in the same place for long and double:
            bool aIsNegative = rawBitsA < 0;
            bool bIsNegative = rawBitsB < 0;