[std-interval] detecting NaN
eliasen at mindspring.com
Tue Jun 6 00:40:01 PDT 2006
Alan Eliasen wrote:
>> So, again, without lack of evidence to the contrary, I stand by my
>> assertion that isnan() is the only standard function available to
>> detect if a number is a NaN or not, and it can't distinguish
>> between quiet and signaling NaNs.
Lee Winter wrote:
> Do you not like the use of fpclassify() to detect NaNs? On x86
> platforms there is hardware support for classification based on the
> fxam instruction.
Thanks; I was not aware of fpclassify, only the boolean conditions
like isnan(). It appears from the documentation in gcc 4.1.1 that
isnan() "returns a non-zero value if (fpclassify(x) == FP_NAN)", so one
is simply defined in terms of the other, and confers no clear advantages
when testing for NaN.
Still, it doesn't affect my point that there isn't a standardized
function to distinguish between quiet and signaling NaNs, other than
working directly with the bit patterns as I noted in my first posting on
Alan Eliasen | "When trouble is solved before it
eliasen at mindspring.com | forms, who calls that clever?"
http://futureboy.us/ | --Sun Tzu
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