Marshal a 'Single' or 'Double'

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Peter - 23 Nov 2007 00:33 GMT

In coping data between managed and native code, I make use of the Marshal
class methods, ReadInt32, Copy, StructureToPtr, etc. However, I also want to
copy Double and Single values, but given that there's is no ReadSingle and
ReadDouble, what's the best way to do the copy?

Thanks
Peter.

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Mattias Sjögren - 23 Nov 2007 06:17 GMT

>In coping data between managed and native code, I make use of the Marshal
>class methods, ReadInt32, Copy, StructureToPtr, etc. However, I also want to
>copy Double and Single values, but given that there's is no ReadSingle and
>ReadDouble, what's the best way to do the copy?

A couple of different options with varying performance.

- Use Marshal.Copy to a single[1] or double[1].

- Use Marshal.PtrToStructure. I believe it handles simple types as
well. If not you can use a dummy wrapper type:

struct YourDouble { public double d; }

- For doubles, use Marshal.ReadInt64 followed by
BitConverter.Int64BitsToDouble.

- Use the CopyMemory windows API.

[DllImport("kernel32.dll")]
static extern void RtlMoveMemory(out double dest, IntPtr src, int cb);

- If you use a language with pointer support (C# with unsafe code or
C++) you can cast to a real double* or single* and simply dereference
it.

Mattias

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Mattias Sjögren [C# MVP] mattias @ mvps.org
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Peter - 24 Nov 2007 03:40 GMT

Mattias,

Thanks for your reply.

I have gone the 'dummy wrapper' suggestion below.

You indicate that some of your suggestions are better performers than
others, are your suggestions in any particular order?

Thanks
Peter.

>>In coping data between managed and native code, I make use of the Marshal
>>class methods, ReadInt32, Copy, StructureToPtr, etc. However, I also want
[quoted text clipped - 24 lines]
>
> Mattias

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Marshal a 'Single' or 'Double'

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