[boost] Re: [hash] Expected behaviour of hashing quiet NaN?

From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2005-04-19 07:14:53

Daniel James wrote:
> Markus Schöpflin <markus.schoepflin <at> comsoft.de> writes:
> 
>>I have to admit, following Victor's argumentation, I don't see the 
>>fundamental difference between the failures on SunOS and on Tru64.
> 
> On SunOS gcc the hash function is giving the same result for 
> std::numeric_limits<long double>::max(), std::numeric_limits<long double>
> ::max()/2 and std::numeric_limits<long double>::max()/4. This indicates that 
> the function for getting its exponent is probably treating the value as a 
> double. If you're using a long double you want to take advantage of its 
> increased accuracy and range but the hash function is loosing that information 
> and so could give bad results under certain circumstances.

Thanks for the explanation.

>>>The tests don't supply a general purpose hash testing suite, but one 
>>>that tests whether the hash functions are doing what I expect.
>>
>>I don't get you there. The tests are supposed to tell whether the hash 
>>library works ok or not on some particular compiler/platform. If some of 
>>the tests fail, I have to assume (from a user's point of view) that the 
>>library will not work reliably for me. (Especially as these are not 
>>compilation failures but runtime failures.)
> 
> This isn't released code, I wouldn't assume that it would work reliably at all. 
> It might not even be fully included in the next release. When we reach the code 
> freeze I'll add annotations to the tests to explain what's going on. I might 
> also make some changes so that only real failures show up - but taking this too 
> far would make the tests essentially useless. (An early version didn't take 
> into account a float's sign, it met the hash specifications, but I'd consider 
> that a bug).

I was under the impression that hash functions would be part of the 
upcoming release. Just to clarify, my intention was not to complain about a 
not working hash library but to understand/clarify _why_ the regression 
reports showed a failure for this platform.

>>Maybe you could change the tests to just print the hash values on stdout?
> 
> But then the results won't show up on the summary. At the moment it's more 
> useful that the test summary shows me useful information.

Do you know about "always_show_run_output"? You just have to add 
"<test-info>always_show_run_output" to your hash-test rule to always see 
the output of the test runs.

Markus