[Mono-list] float p/invoke

Robert Jordan robertj at gmx.net
Thu Nov 9 16:58:31 EST 2006

Andreas Färber wrote:
> Hello,
> I'm facing a weird marshalling issue...
> The Objective-C runtime on OS X exposes a method:
> id objc_msgSend(id, SEL, ...);    // with id and SEL pointers
> I marshal it as IntPtr objc_msgSend(IntPtr, IntPtr, ...) using an SRE  
> p/invoke method factory.
> This has worked fine so far, but now I noticed some marshalling  
> problems. The method's semantic return value is not always a pointer  
> but is apparently also used for int, unsigned int - which works fine  
> through IntPtr casting, but not for float. To my understanding float  
> is single-precision floating point number, thus 32 bits or 4 bytes  
> wide and identical to IntPtr.Size in a 32-bit environment.

Floating point results are not returned the same way
as scalar results. For example, the x86 ABI returns
scalars in the EAX register, while floats are returned
in a FPU register => it's impossible to marshal them using
an IntPtr result type.


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