[Discuss] Test for positive gives wacko results for underflowed values for the gcc compiler suite (including the gcc compiler, and g77 and gfortran compilers)

[Alan W. Irwin]

On 2007-06-25 20:31-0700 pw wrote:

> Alan W. Irwin wrote:
>> If the skipped normalization hypothesis is correct, gcc (or any compiler) 
>> on
>> non-Intel platforms without the 80-bit registers should give correct 
>> results
>> for my test case. Does anybody have test results for such platforms? Also,
>> from Peter's test it looks like the windows C compiler skips the
>> normalization step on Intel hardware, and it would be interesting to see 
>> if
>> the Intel compiler also has the same issue.
>> 
>
> gcc using the -fshort-double flag for compilation....

but that is a 32-bit option where all the underflow limits are quite
different.  As I demonstrated yesterday you can get the same bad results for
32-bit if you pick your x and xscale values judiciously.

Alan
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Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

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(lbproject.sf.net).
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