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CUDA-x86.

How to specify real*16 data on AMD64 machines?

 
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Johnix



Joined: 30 Jul 2004
Posts: 3

PostPosted: Sun Feb 20, 2005 7:01 pm    Post subject: How to specify real*16 data on AMD64 machines? Reply with quote

Hi,

As we know, doube precision for 32-bit CPU means 32x2=64 bits, so naturally for 64-bit CPU it shoulbe be 128 bits. But I couldn't find the pgf90's switch to turn on 128-bit double precision on my AMD64 machine. Has anyone tried this before? I tried Sun's f90 and intel ifc, they both seem to have this switch such as '-xtypemap=double:128' and '-r16'. pgf90 should also have similar switch, but I just couldn't find it.

Thanks!
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mkcolg



Joined: 30 Jun 2004
Posts: 5952
Location: The Portland Group Inc.

PostPosted: Mon Feb 21, 2005 9:54 am    Post subject: Reply with quote

Hi Johnix,

We do not natively support REAL*16. Since 128-bit floating point calculations are not supported by the hardware, such calculation need to be handled by extremely slow software emulation. Most users who want REAL*16 tell us they would not use such a package if the performance did not match that of REAL*8. We have considered supporting REAL*16 by using the 80-bit x87 FPU for calculations as some other compiler vendors do, but this is really REAL*10 and calling it REAL*16 doesn't actually make it so. So our choices are to either cheat, or spend a lot of time developing a emulation package very few people would use.

For those of you who need precsion over performance, there are several good freely available quad precision emulation packages out on the web. We cannot recommend any particular package, but you should be able to find one that works for you.

Thanks,
Mat
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