# Double.EpsilonDouble.EpsilonDouble.EpsilonDouble.Epsilon Field

## 定义

``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``

## 注解

``````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
``````

``````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
``````

Epsilon 属性不是 Double 类型的常规精度度量值;它仅适用于值为零或指数为-1022 的 @no__t 2 实例。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.

@No__t-0 属性的值不等效于计算机 epsilon，后者表示相对错误的上限，原因是浮点算术的舍入。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.