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Checking for a NAN value

 
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nero1232
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Joined: 08 Mar 2017
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PostPosted: Fri Mar 17, 2017 5:45 pm    Post subject: Checking for a NAN value Reply with quote

Hi,

Is it possible to check if an address contains a NAN float value? I am doing some assembly coding and occasionally my float address will contain NAN, so in this case I want to rewrite it.

Thanks
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ParkourPenguin
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Joined: 06 Jul 2014
Posts: 4275

PostPosted: Fri Mar 17, 2017 6:24 pm    Post subject: Reply with quote

There are a few ways. ucomiss is probably the easiest:
Code:
movss xmm0,[addr]
ucomiss xmm0,xmm0
jnp @f
  // NaN, do something
  jmp exit
@@:
  // not NaN, do something else
exit:

You could also look at how the float is encoded. See IEEE standard 754 (namely binary32 and binary64) for a brief overview.

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