26

假设我们有一个 System.Decimal 数字。

举个例子，我们来看一个 ToString() 表示如下：

d.ToString() = "123.4500"

关于这个十进制可以说以下内容。出于我们的目的，比例定义为小数点右侧的位数。有效比例类似，但忽略小数部分中出现的任何尾随零。（换句话说，这些参数的定义类似于 SQL 小数加上一些附加参数，以说明 System.Decimal 小数部分尾随零的概念。）

  • 精度：7
  • 规模：4
  • 有效精度：5
  • 有效规模：2

给定一个任意的 System.Decimal，我怎样才能有效地计算所有这四个参数而不转换为字符串并检查字符串？该解决方案可能需要 Decimal.GetBits。

更多示例：

Examples Precision  Scale  EffectivePrecision  EffectiveScale
0        1 (?)      0      1 (?)               0
0.0      2 (?)      1      1 (?)               0
12.45    4          2      4                   2
12.4500  6          4      4                   2
770      3          0      3                   0

(?) 或者将这些精度解释为零也可以。

4

5 回答 5

30

是的，您需要使用Decimal.GetBits. 不幸的是，您必须使用 96 位整数，并且 .NET 中没有简单的整数类型可以处理 96 位。另一方面，您可能会使用Decimal自己...

这是一些产生与您的示例相同的数字的代码。希望你觉得它有用 ：）

using System;

public class Test
{
    static public void Main(string[] x)
    {
        ShowInfo(123.4500m);
        ShowInfo(0m);
        ShowInfo(0.0m);
        ShowInfo(12.45m);
        ShowInfo(12.4500m);
        ShowInfo(770m);
    }

    static void ShowInfo(decimal dec)
    {
        // We want the integer parts as uint
        // C# doesn't permit int[] to uint[] conversion,
        // but .NET does. This is somewhat evil...
        uint[] bits = (uint[])(object)decimal.GetBits(dec);


        decimal mantissa = 
            (bits[2] * 4294967296m * 4294967296m) +
            (bits[1] * 4294967296m) +
            bits[0];

        uint scale = (bits[3] >> 16) & 31;

        // Precision: number of times we can divide
        // by 10 before we get to 0        
        uint precision = 0;
        if (dec != 0m)
        {
            for (decimal tmp = mantissa; tmp >= 1; tmp /= 10)
            {
                precision++;
            }
        }
        else
        {
            // Handle zero differently. It's odd.
            precision = scale + 1;
        }

        uint trailingZeros = 0;
        for (decimal tmp = mantissa;
             tmp % 10m == 0 && trailingZeros < scale;
             tmp /= 10)
        {
            trailingZeros++;
        }

        Console.WriteLine("Example: {0}", dec);
        Console.WriteLine("Precision: {0}", precision);
        Console.WriteLine("Scale: {0}", scale);
        Console.WriteLine("EffectivePrecision: {0}",
                          precision - trailingZeros);
        Console.WriteLine("EffectiveScale: {0}", scale - trailingZeros);
        Console.WriteLine();
    }
}
于 2009-04-18T20:14:11.033 回答
27

当我需要在将十进制值写入数据库之前验证精度和比例时，我遇到了这篇文章。实际上，我想出了一种不同的方法来使用 System.Data.SqlTypes.SqlDecimal 来实现这一点，结果证明它比这里讨论的其他两种方法更快。

 static DecimalInfo SQLInfo(decimal dec)

     {

         System.Data.SqlTypes.SqlDecimal x;
         x = new  System.Data.SqlTypes.SqlDecimal(dec);                     
         return new DecimalInfo((int)x.Precision, (int)x.Scale, (int)0);
     }
于 2010-12-14T11:06:59.317 回答
11

使用 ToString 比 Jon Skeet 的解决方案快大约 10 倍。虽然这相当快，但这里的挑战（如果有任何接受者！）是击败 ToString 的性能。

我从以下测试程序得到的性能结果是： ShowInfo 239 ms FastInfo 25 ms

using System;
using System.Diagnostics;
using System.Globalization;

public class Test
{
    static public void Main(string[] x)
    {
        Stopwatch sw1 = new Stopwatch();
        Stopwatch sw2 = new Stopwatch();

        sw1.Start();
        for (int i = 0; i < 10000; i++)
        {
            ShowInfo(123.4500m);
            ShowInfo(0m);
            ShowInfo(0.0m);
            ShowInfo(12.45m);
            ShowInfo(12.4500m);
            ShowInfo(770m);
        }
        sw1.Stop();

        sw2.Start();
        for (int i = 0; i < 10000; i++)
        {
            FastInfo(123.4500m);
            FastInfo(0m);
            FastInfo(0.0m);
            FastInfo(12.45m);
            FastInfo(12.4500m);
            FastInfo(770m);
        }
        sw2.Stop();

        Console.WriteLine(sw1.ElapsedMilliseconds);
        Console.WriteLine(sw2.ElapsedMilliseconds);
        Console.ReadLine();
    }

    // Be aware of how this method handles edge cases.
    // A few are counterintuitive, like the 0.0 case.
    // Also note that the goal is to report a precision
    // and scale that can be used to store the number in
    // an SQL DECIMAL type, so this does not correspond to
    // how precision and scale are defined for scientific
    // notation. The minimal precision SQL decimal can
    // be calculated by subtracting TrailingZeros as follows:
    // DECIMAL(Precision - TrailingZeros, Scale - TrailingZeros).
    //
    //     dec Precision Scale TrailingZeros
    // ------- --------- ----- -------------
    //   0             1     0             0
    // 0.0             2     1             1
    // 0.1             1     1             0
    // 0.01            2     2             0 [Diff result than ShowInfo]
    // 0.010           3     3             1 [Diff result than ShowInfo]
    // 12.45           4     2             0
    // 12.4500         6     4             2
    // 770             3     0             0
    static DecimalInfo FastInfo(decimal dec)
    {
        string s = dec.ToString(CultureInfo.InvariantCulture);

        int precision = 0;
        int scale = 0;
        int trailingZeros = 0;
        bool inFraction = false;
        bool nonZeroSeen = false;

        foreach (char c in s)
        {
            if (inFraction)
            {
                if (c == '0')
                    trailingZeros++;
                else
                {
                    nonZeroSeen = true;
                    trailingZeros = 0;
                }

                precision++;
                scale++;
            }
            else
            {
                if (c == '.')
                {
                    inFraction = true;
                }
                else if (c != '-')
                {
                    if (c != '0' || nonZeroSeen)
                    {
                        nonZeroSeen = true;
                        precision++;
                    }
                }
            }
        }

        // Handles cases where all digits are zeros.
        if (!nonZeroSeen)
            precision += 1;

        return new DecimalInfo(precision, scale, trailingZeros);
    }

    struct DecimalInfo
    {
        public int Precision { get; private set; }
        public int Scale { get; private set; }
        public int TrailingZeros { get; private set; }

        public DecimalInfo(int precision, int scale, int trailingZeros)
            : this()
        {
            Precision = precision;
            Scale = scale;
            TrailingZeros = trailingZeros;
        }
    }

    static DecimalInfo ShowInfo(decimal dec)
    {
        // We want the integer parts as uint
        // C# doesn't permit int[] to uint[] conversion,
        // but .NET does. This is somewhat evil...
        uint[] bits = (uint[])(object)decimal.GetBits(dec);


        decimal mantissa =
            (bits[2] * 4294967296m * 4294967296m) +
            (bits[1] * 4294967296m) +
            bits[0];

        uint scale = (bits[3] >> 16) & 31;

        // Precision: number of times we can divide
        // by 10 before we get to 0 
        uint precision = 0;
        if (dec != 0m)
        {
            for (decimal tmp = mantissa; tmp >= 1; tmp /= 10)
            {
                precision++;
            }
        }
        else
        {
            // Handle zero differently. It's odd.
            precision = scale + 1;
        }

        uint trailingZeros = 0;
        for (decimal tmp = mantissa;
            tmp % 10m == 0 && trailingZeros < scale;
            tmp /= 10)
        {
            trailingZeros++;
        }

        return new DecimalInfo((int)precision, (int)scale, (int)trailingZeros);
    }
}
于 2009-04-18T21:56:32.877 回答
0 
public static class DecimalExtensions
{
    public static int GetPrecision(this decimal value)
    {
        return GetLeftNumberOfDigits(value) + GetRightNumberOfDigits(value);
    }

    public static int GetScale(this decimal value)
    {
        return GetRightNumberOfDigits(value);
    }
    /// <summary>
    /// Number of digits to the right of the decimal point without ending zeros
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public static int GetRightNumberOfDigits(this decimal value)
    {
        var text = value.ToString(System.Globalization.CultureInfo.InvariantCulture).TrimEnd('0');
        var decpoint = text.IndexOf(System.Globalization.CultureInfo.InvariantCulture.NumberFormat.NumberDecimalSeparator);
        if (decpoint < 0)
            return 0;
        return text.Length - decpoint - 1;
    }

    /// <summary>
    /// Number of digits to the left of the decimal point without starting zeros
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public static int GetLeftNumberOfDigits(this decimal value)
    {
        var text = Math.Abs(value).ToString(System.Globalization.CultureInfo.InvariantCulture).TrimStart('0');
        var decpoint = text.IndexOf(System.Globalization.CultureInfo.InvariantCulture.NumberFormat.NumberDecimalSeparator);
        if (decpoint == -1)
            return text.Length;
        return decpoint;
    }
}

我的解决方案与 NUMBER(p,s) DataType 的 Oracle 精度和比例定义兼容：

https://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm#i16209

问候。

于 2016-06-06T14:28:14.640 回答
0

我目前确实有类似的问题，但我不仅需要比例，还需要尾数作为整数。根据上面的解决方案，请在下面找到我能想到的最快的解决方案。统计数据：“ViaBits”在我的机器上进行 7,000,000 次检查需要 2,000 毫秒。“ViaString”同样的任务需要 4,000 毫秒。

    public class DecimalInfo {

    public BigInteger Mantisse { get; private set; }
    public SByte Scale { get; private set; }
    private DecimalInfo() {
    }

    public static DecimalInfo Get(decimal d) {
        //ViaBits is faster than ViaString.
        return ViaBits(d);
    }

    public static DecimalInfo ViaBits(decimal d) {
        //This is the fastest, I can come up with.
        //Tested against the solutions from http://stackoverflow.com/questions/763942/calculate-system-decimal-precision-and-scale
        if (d == 0) {
            return new DecimalInfo() {
                Mantisse = 0,
                Scale = 0,
            };
        } else {
            byte scale = (byte)((Decimal.GetBits(d)[3] >> 16) & 31);
            //Calculating the mantisse from the bits 0-2 is slower.
            if (scale > 0) {
                if ((scale & 1) == 1) {
                    d *= 10m;
                }
                if ((scale & 2) == 2) {
                    d *= 100m;
                }
                if ((scale & 4) == 4) {
                    d *= 10000m;
                }
                if ((scale & 8) == 8) {
                    d *= 100000000m;
                }
                if ((scale & 16) == 16) {
                    d *= 10000000000000000m;
                }
            }
            SByte realScale = (SByte)scale;
            BigInteger scaled = (BigInteger)d;
            //Just for bigger steps, seems reasonable.
            while (scaled % 10000 == 0) {
                scaled /= 10000;
                realScale -= 4;
            }
            while (scaled % 10 == 0) {
                scaled /= 10;
                realScale--;
            }
            return new DecimalInfo() {
                Mantisse = scaled,
                Scale = realScale,
            };
        }
    }

    public static DecimalInfo ViaToString(decimal dec) {
        if (dec == 0) {
            return new DecimalInfo() {
                Mantisse = 0,
                Scale = 0,
            };
        } else {
            //Is slower than "ViaBits".
            string s = dec.ToString(CultureInfo.InvariantCulture);

            int scale = 0;
            int trailingZeros = 0;
            bool inFraction = false;
            foreach (char c in s) {
                if (inFraction) {
                    if (c == '0') {
                        trailingZeros++;
                    } else {
                        trailingZeros = 0;
                    }
                    scale++;
                } else {
                    if (c == '.') {
                        inFraction = true;
                    } else if (c != '-') {
                        if (c == '0'){
                            trailingZeros ++;
                        } else {
                            trailingZeros = 0;
                        }
                    }
                }
            }

            if (inFraction) {
                return new DecimalInfo() {
                    Mantisse = BigInteger.Parse(s.Replace(".", "").Substring(0, s.Length - trailingZeros - 1)),
                    Scale = (SByte)(scale - trailingZeros),
                };
            } else {
                return new DecimalInfo() {
                    Mantisse = BigInteger.Parse(s.Substring(0, s.Length - trailingZeros)),
                    Scale = (SByte)(scale - trailingZeros),
                };
            }
        }
    }
}
于 2016-08-15T10:56:26.047 回答