How can I copy the bits from a double to a long and back.

Question

I am wanting to copy the bits from a double precision floating point variable into a long variable for analysis. In some instances, I will need to alter some bits and then copy the bits of the long back to the double.
What is the quickest and/or easiest way to do that using Visual Basic .net?

Answer 1

Check an example:

Dim d As Double = 1.2345E+67

' Double to Long '
Dim b As Byte() = BitConverter.GetBytes(d)
Dim l As Long = BitConverter.ToInt64(b)

' Long to Double '
Dim b2 As Byte() = BitConverter.GetBytes(l)
Dim d2 As Double = BitConverter.ToDouble(b2)

Instead of modifying the long, you can modify the bytes of array.

Answer 2

Hi @Jeff Ayers ,
I'm not sure what the result you want is.
The code below may have what you want.

        Dim d1 As Double = 12345.6789  
        Dim d2 As Double  
        Dim l1 = Convert.ToInt64(d1)  
        Dim l2 As Long  
        Dim l3 As Long  
        Dim ind = d1.ToString.IndexOf(".")  
        l2 = d1.ToString.Split(".")(0)  
        l3 = d1.ToString.Replace(".", "")  
        d2 = l3.ToString.Insert(ind, ".")  

d1=12345.6789
l1=12346 Converting directly with convert.toint32 will lose the fractional part and precision
l2=12345 After converting to a string, use split to get the part before the decimal point
l3=123456789 Remove decimal point after converting to string
d2=12345.6789 Add a decimal point in the original position
Hope these are helpful.
Otherwise please provide more information to help us understand what the result you want.
Best Regards.
Jiachen Li

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