Double.Epsilon フィールド

定義

ゼロより大きい最小の Double 値を表します。Represents the smallest positive Double value that is greater than zero. このフィールドは定数です。This field is constant.

public: double Epsilon = 4.94065645841247E-324;
public const double Epsilon = 4.94065645841247E-324;
val mutable Epsilon : double
Public Const Epsilon As Double  = 4.94065645841247E-324

フィールド値

注釈

Epsilon プロパティの値は、Double インスタンスの値が0の場合に数値演算または比較に有意な最小の正 Double 値を反映します。The value of the Epsilon property reflects the smallest positive Double value that is significant in numeric operations or comparisons when the value of the Double instance is zero. たとえば、次のコードは、0と Epsilon が等しくない値であると見なされ、Epsilon の0と半分の値は等しいと見なされることを示しています。For example, the following code shows that zero and Epsilon are considered to be unequal values, whereas zero and half the value of Epsilon are considered to be equal.

using System;

public class Example
{
   public static void Main()
   {
      double[] values = { 0, Double.Epsilon, Double.Epsilon * .5 };
      
      for (int ctr = 0; ctr <= values.Length - 2; ctr++)
      {
         for (int ctr2 = ctr + 1; ctr2 <= values.Length - 1; ctr2++)
         {
            Console.WriteLine("{0:r} = {1:r}: {2}", 
                              values[ctr], values[ctr2],  
                              values[ctr].Equals(values[ctr2]));
         }
         Console.WriteLine();
      }      
   }
}
// The example displays the following output:
//       0 = 4.94065645841247E-324: False
//       0 = 0: True
//       
//       4.94065645841247E-324 = 0: False
Module Example
   Public Sub Main()
      Dim values() As Double = { 0, Double.Epsilon, Double.Epsilon * .5 }
      
      For ctr As Integer = 0 To values.Length - 2
         For ctr2 As Integer = ctr + 1 To values.Length - 1
            Console.WriteLine("{0:r} = {1:r}: {2}", _
                              values(ctr), values(ctr2), _ 
                              values(ctr).Equals(values(ctr2)))
         Next
         Console.WriteLine()
      Next      
   End Sub
End Module
' The example displays the following output:
'       0 = 4.94065645841247E-324: False
'       0 = 0: True
'       
'       4.94065645841247E-324 = 0: False

より正確には、浮動小数点形式は、符号、52ビットの仮数または有効桁、および11ビットの指数で構成されます。More precisely, the floating point format consists of a sign, a 52-bit mantissa or significand, and an 11-bit exponent. 次の例に示すように、0の指数は-1022、仮数は0です。As the following example shows, zero has an exponent of -1022 and a mantissa of 0. Epsilon の指数は-1022、仮数は1です。Epsilon has an exponent of -1022 and a mantissa of 1. これは、Epsilon が0よりも大きい最小の正の Double 値であり、可能な最小値を表し、指数が-1022 の Double に対して可能な最小のインクリメントであることを意味します。This means that Epsilon is the smallest positive Double value greater than zero and represents the smallest possible value and the smallest possible increment for a Double whose exponent is -1022.

using System;

public class Example
{
   public static void Main()
   {
      double[] values = { 0.0, Double.Epsilon };
      foreach (var value in values) {
         Console.WriteLine(GetComponentParts(value));
         Console.WriteLine();
      }   
   }

   private static string GetComponentParts(double value)
   {
      string result = String.Format("{0:R}: ", value);
      int indent = result.Length;

      // Convert the double to an 8-byte array.
      byte[] bytes = BitConverter.GetBytes(value);
      // Get the sign bit (byte 7, bit 7).
      result += String.Format("Sign: {0}\n", 
                              (bytes[7] & 0x80) == 0x80 ? "1 (-)" : "0 (+)");

      // Get the exponent (byte 6 bits 4-7 to byte 7, bits 0-6)
      int exponent = (bytes[7] & 0x07F) << 4;
      exponent = exponent | ((bytes[6] & 0xF0) >> 4);  
      int adjustment = exponent != 0 ? 1023 : 1022;
      result += String.Format("{0}Exponent: 0x{1:X4} ({1})\n", new String(' ', indent), exponent - adjustment);

      // Get the significand (bits 0-51)
      long significand = ((bytes[6] & 0x0F) << 48); 
      significand = significand | ((long) bytes[5] << 40);
      significand = significand | ((long) bytes[4] << 32);
      significand = significand | ((long) bytes[3] << 24);
      significand = significand | ((long) bytes[2] << 16);
      significand = significand | ((long) bytes[1] << 8);
      significand = significand | bytes[0];    
      result += String.Format("{0}Mantissa: 0x{1:X13}\n", new String(' ', indent), significand);    

      return result;   
   }
}
//       // The example displays the following output:
//       0: Sign: 0 (+)
//          Exponent: 0xFFFFFC02 (-1022)
//          Mantissa: 0x0000000000000
//       
//       
//       4.94065645841247E-324: Sign: 0 (+)
//                              Exponent: 0xFFFFFC02 (-1022)
//                              Mantissa: 0x0000000000001
Module Example
   Public Sub Main()
      Dim values() As Double = { 0.0, Double.Epsilon }
      For Each value In values
         Console.WriteLine(GetComponentParts(value))
         Console.WriteLine()
      Next   
   End Sub

   Private Function GetComponentParts(value As Double) As String
      Dim result As String =  String.Format("{0:R}: ", value)
      Dim indent As Integer =  result.Length

      ' Convert the double to an 8-byte array.
      Dim bytes() As Byte = BitConverter.GetBytes(value)
      ' Get the sign bit (byte 7, bit 7).
      result += String.Format("Sign: {0}{1}", 
                              If((bytes(7) And &H80) = &H80, "1 (-)", "0 (+)"),
                              vbCrLf)

      ' Get the exponent (byte 6 bits 4-7 to byte 7, bits 0-6)
      Dim exponent As Integer =  (bytes(7) And &H07F) << 4
      exponent = exponent Or ((bytes(6) And &HF0) >> 4)  
      Dim adjustment As Integer = If(exponent <> 0, 1023, 1022)
      result += String.Format("{0}Exponent: 0x{1:X4} ({1}){2}", 
                              New String(" "c, indent), exponent - adjustment,
                              vbCrLf)

      ' Get the significand (bits 0-51)
      Dim significand As Long =  ((bytes(6) And &H0F) << 48) 
      significand = significand Or (bytes(5) << 40)
      significand = significand Or (bytes(4) << 32)
      significand = significand Or (bytes(3) << 24)
      significand = significand Or (bytes(2) << 16)
      significand = significand Or (bytes(1) << 8)
      significand = significand Or bytes(0)    
      result += String.Format("{0}Mantissa: 0x{1:X13}{2}", 
                              New String(" "c, indent), significand, vbCrLf)    

      Return result   
   End Function
End Module
' The example displays the following output:
'       0: Sign: 0 (+)
'          Exponent: 0xFFFFFC02 (-1022)
'          Mantissa: 0x0000000000000
'       
'       
'       4.94065645841247E-324: Sign: 0 (+)
'                              Exponent: 0xFFFFFC02 (-1022)
'                              Mantissa: 0x0000000000001

ただし、Epsilon プロパティは、Double 型の有効桁数の一般的な尺度ではありません。この値は、0または-1022 の指数を持つ Double インスタンスにのみ適用されます。However, the Epsilon property is not a general measure of precision of the Double type; it applies only to Double instances that have a value of zero or an exponent of -1022.

注意

Epsilon プロパティの値は、浮動小数点演算における丸め処理による相対誤差の上限を表すコンピューターイプシロンと等価ではありません。The value of the Epsilon property is not equivalent to machine epsilon, which represents the upper bound of the relative error due to rounding in floating-point arithmetic.

この定数の値は 4.94065645841247 e-324 です。The value of this constant is 4.94065645841247e-324.

意味が低い2つの浮動小数点数は、少なくとも有効桁数が異なるため、等しいと比較できない場合があります。Two apparently equivalent floating-point numbers might not compare equal because of differences in their least significant digits. たとえば、 C#式の (double)1/3 == (double)0.33333は、左辺の除算演算には最大有効桁数があり、右側の定数は指定された桁数だけであるため、等しいかどうかを比較しません。For example, the C# expression, (double)1/3 == (double)0.33333, does not compare equal because the division operation on the left side has maximum precision while the constant on the right side is precise only to the specified digits. 2つの浮動小数点数を等しいと見なすことができるかどうかを決定するカスタムアルゴリズムを作成する場合は、アルゴリズムを Epsilon 定数の値に基づいて、2つの差の許容される絶対余白を確立することはお勧めしません。等しいと見なされる値。If you create a custom algorithm that determines whether two floating-point numbers can be considered equal, we do not recommend that you base your algorithm on the value of the Epsilon constant to establish the acceptable absolute margin of difference for the two values to be considered equal. (通常、この余白の差は Epsilonよりも多くの回数になります)。2つの倍精度浮動小数点値の比較の詳細については、「Double」と「Equals(Double)」を参照してください。(Typically, that margin of difference is many times greater than Epsilon.) For information about comparing two double-precision floating-point values, see Double and Equals(Double).

プラットフォームに関する注意事項Platform Notes

ARM システムでは、Epsilon 定数の値が小さすぎて検出できないため、0になります。On ARM systems, the value of the Epsilon constant is too small to be detected, so it equates to zero. 代わりに、2.2250738585072014 E-308 と等しい別のイプシロン値を定義できます。You can define an alternative epsilon value that equals 2.2250738585072014E-308 instead.

適用対象