Hardware or System Incompatibility

Jan Bottorff janb at pmatrix.com
Wed Feb 17 19:54:05 UTC 1999


At 02:18 PM 2/17/99 -0500, William O. Dargel wrote:
>Ah, the -0.0 appears to be a 'negative' version of NaN. It really
>surprises me though that NaN seems to be equal to _any_ Float value. 
>Is that normal behavior?

I believe the NaN your talking about is know as a quiet NaN (QNaN). There
are also noisy NaN's with a different bit encoding. Quiet NaN are supposed
to just magically get ignored, so am not surprised they are equal to any
float value. 

There are three flavors of NaN's on Intel processors. Quiet NaN's (QNaN)
with a bit encoding of sign=X, exponent=11..11, fractional
significand=1X..xx, noisy NaN's (SNaN) with a bit encoding of sign=X,
exponent=11..11, fractional significand=0X..XX(must be non-zero fractional
part), and also Real Indefinite (subset of QNaN?) with a bit encoding of
sign=1, exponent=11..11, fractional significand=10..00. 

I reported all this to Dan.

- Jan
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