For days I&#39;m fighting against a weird bug. <div><br></div><div>My Haskell code calls into a C function residing in a DLL (I&#39;m on Windows, the DLL is generated using Visual Studio). This C function computes a floating point expression. However, the floating point result is incorrect.</div>
<div><br></div><div>I think I found the source of the problem: the C code expects that all the Intel&#39;s x86&#39;s floating point register tag bits are set to 1, but it seems the Haskell code does not preserve that.</div>
<div><br></div><div>Since the x86 has all kinds of<a href="http://www.informit.com/articles/article.aspx?p=770362"> floating point weirdness</a> - it is both a stack based and register based system - so it is crucially important that generated code plays nice. For example, when using MMX one must <a href="http://msdn.microsoft.com/en-us/library/590b9ks9(VS.80).aspx">always emit an EMMS instruction</a> to clear these tag bits.</div>
<div><br></div><div>If I manually clear these tags bits, my code works fine.</div><div><br></div><div><div>Is this something other people encountered as well? I&#39;m trying to make a very simple test case to reproduce the behavior...</div>
<div><br></div><div>I&#39;m not sure if this is a visual C compiler bug, GHC bug, or something I&#39;m doing wrong...</div><div><br></div></div><div>Is it possible to annotate a foreign imported C function to tell the Haskell code generator the functioin is using floating point registers somehow?</div>
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