Single.Equals Method (Single)

 
System_CAPS_noteNote

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Returns a value indicating whether this instance and a specified Single object represent the same value.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

Public Function Equals (
	obj As Single
) As Boolean

Parameters

obj
Type: System.Single

An object to compare with this instance.

Return Value

Type: System.Boolean

true if obj is equal to this instance; otherwise, false.

This method implements the System.IEquatable(Of T) interface, and performs slightly better than Equals because it does not have to convert the obj parameter to an object.

Depending on your programming language, it might be possible to code an Equals method where the parameter type has fewer bits (is narrower) than the instance type. This is possible because some programming languages perform an implicit widening conversion that represents the parameter as a type with as many bits as the instance.

For example, suppose the instance type is Single and the parameter type is Int32. The Microsoft C# compiler generates instructions to represent the value of the parameter as a Single object, and then generates a Single.Equals(Single) method that compares the values of the instance and the widened representation of the parameter.

Consult your programming language's documentation to determine if its compiler performs implicit widening conversions of numeric types. For more information, see the Type Conversion Tables in the .NET Framework topic.

TheEquals method should be used with caution, because two apparently equivalent values can be unequal because of the differing precision of the two values. The following example reports that the Single value .3333 and the Single returned by dividing 1 by 3 are unequal.

' Initialize two singles with apparently identical values
Dim single1 As Single = .33333
Dim single2 As Single = 1/3
' Compare them for equality
Console.WriteLine(single1.Equals(single2))    ' displays False

One comparison technique that avoids the problems associated with comparing for equality involves defining an acceptable margin of difference between two values (such as .01% of one of the values). If the absolute value of the difference between the two values is less than or equal to that margin, the difference is likely to be an outcome of differences in precision and, therefore, the values are likely to be equal. The following example uses this technique to compare .33333 and 1/3, which are the two Single values that the previous code example found to be unequal.

' Initialize two singles with apparently identical values
Dim single1 As Single = .33333
Dim single2 As Single = 1/3
' Define the tolerance for variation in their values
Dim difference As Single = Math.Abs(single1 * .0001f)

' Compare the values
' The output to the console indicates that the two values are equal
If Math.Abs(single1 - single2) <= difference Then
   Console.WriteLine("single1 and single2 are equal.")
Else
   Console.WriteLine("single1 and single2 are unequal.")
End If

In this case, the values are equal.

System_CAPS_noteNote

Because Epsilon defines the minimum expression of a positive value whose range is near zero, the margin of difference must be greater than Epsilon. Typically, it is many times greater than Epsilon. Because of this, we recommend that you do not use Epsilon when comparing Double values for equality.

A second technique that avoids the problems associated with comparing for equality involves comparing the difference between two floating-point numbers with some absolute value. If the difference is less than or equal to that absolute value, the numbers are equal. If it is greater, the numbers are not equal. One way to do this is to arbitrarily select an absolute value. However, this is problematic, because an acceptable margin of difference depends on the magnitude of the Single values. A second way takes advantage of a design feature of the floating-point format: The difference between the mantissa components in the integer representations of two floating-point values indicates the number of possible floating-point values that separates the two values. For example, the difference between 0.0 and Epsilon is 1, because Epsilon is the smallest representable value when working with a Single whose value is zero. The following example uses this technique to compare .33333 and 1/3, which are the two Double values that the previous code example with the Equals(Single) method found to be unequal. Note that the example uses the BitConverter.GetBytes and BitConverter.ToInt32 methods to convert a single-precision floating-point value to its integer representation.

Module Example
   Public Sub Main()
      Dim value1 As Single = .1 * 10
      Dim value2 As Single = 0
      For ctr As Integer =  0 To 9
         value2 += CSng(.1)
      Next

      Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2,
                        HasMinimalDifference(value1, value2, 1))
   End Sub

   Public Function HasMinimalDifference(value1 As Single, value2 As Single, units As Integer) As Boolean
      Dim bytes() As Byte = BitConverter.GetBytes(value1)
      Dim iValue1 As Integer =  BitConverter.ToInt32(bytes, 0)

      bytes = BitConverter.GetBytes(value2)
      Dim iValue2 As Integer =  BitConverter.ToInt32(bytes, 0)

      ' If the signs are different, Return False except for +0 and -0.
      If ((iValue1 >> 31) <> (iValue2 >> 31)) Then
         If value1 = value2 Then
            Return True
         End If           
         Return False
      End If

      Dim diff As Integer =  Math.Abs(iValue1 - iValue2)

      If diff <= units Then
         Return True
      End If

      Return False
   End Function
End Module
' The example displays the following output:
'       1 = 1.00000012: True

The precision of floating-point numbers beyond the documented precision is specific to the implementation and version of the .NET Framework. Consequently, a comparison of two numbers might produce different results depending on the version of the .NET Framework, because the precision of the numbers' internal representation might change.

Notes to Callers:

Compiler overload resolution may account for an apparent difference in the behavior of the two Equals method overloads. If an implicit conversion between the obj argument and a Single is defined and the argument is not typed as an Object, compilers may perform an implicit conversion and call the Equals(Single) method. Otherwise, they call the Equals(Object) method, which always returns false if its obj argument is not a Single value. The following example illustrates the difference in behavior between the two method overloads. In the case of all primitive numeric types except for Double in Visual Basic and except for Decimal and Double in C#, the first comparison returns true because the compiler automatically performs a widening conversion and calls the Equals(Single) method, whereas the second comparison returns false because the compiler calls the Equals(Object) method.

Module Example
   Dim value As Single = 112

   Public Sub Main()
      Dim byte1 As Byte = 112
      Console.WriteLine("value = byte1: {0,16}", value.Equals(byte1))
      TestObjectForEquality(byte1)

      Dim short1 As Short = 112
      Console.WriteLine("value = short1: {0,16}", value.Equals(short1))
      TestObjectForEquality(short1)

      Dim int1 As Integer = 112
      Console.WriteLine("value = int1: {0,18}", value.Equals(int1))
      TestObjectForEquality(int1)

      Dim long1 As Long = 112
      Console.WriteLine("value = long1: {0,17}", value.Equals(long1))
      TestObjectForEquality(long1)

      Dim sbyte1 As SByte = 112
      Console.WriteLine("value = sbyte1: {0,16}", value.Equals(sbyte1))
      TestObjectForEquality(sbyte1)

      Dim ushort1 As UShort = 112
      Console.WriteLine("value = ushort1: {0,16}", value.Equals(ushort1))
      TestObjectForEquality(ushort1)

      Dim uint1 As UInteger = 112
      Console.WriteLine("value = uint1: {0,18}", value.Equals(uint1))
      TestObjectForEquality(uint1)

      Dim ulong1 As ULong = 112
      Console.WriteLine("value = ulong1: {0,17}", value.Equals(ulong1))
      TestObjectForEquality(ulong1)

      Dim dec1 As Decimal = 112d
      Console.WriteLine("value = dec1: {0,20}", value.Equals(dec1))
      TestObjectForEquality(dec1)

      Dim dbl1 As Double = 112
      Console.WriteLine("value = dbl1: {0,20}", value.Equals(dbl1))
      TestObjectForEquality(dbl1)
   End Sub

   Private Sub TestObjectForEquality(obj As Object)
      Console.WriteLine("{0} ({1}) = {2} ({3}): {4}",
                        value, value.GetType().Name,
                        obj, obj.GetType().Name,
                        value.Equals(obj))
      Console.WriteLine()
   End Sub
End Module
' The example displays the following output:
'       value = byte1:             True
'       112 (Single) = 112 (Byte): False
'
'       value = short1:             True
'       112 (Single) = 112 (Int16): False
'
'       value = int1:               True
'       112 (Single) = 112 (Int32): False
'
'       value = long1:              True
'       112 (Single) = 112 (Int64): False
'
'       value = sbyte1:             True
'       112 (Single) = 112 (SByte): False
'
'       value = ushort1:             True
'       112 (Single) = 112 (UInt16): False
'
'       value = uint1:               True
'       112 (Single) = 112 (UInt32): False
'
'       value = ulong1:              True
'       112 (Single) = 112 (UInt64): False
'
'       value = dec1:                 True
'       112 (Single) = 112 (Decimal): False
'
'       value = dbl1:                False
'       112 (Single) = 112 (Double): False

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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