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

From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2005-04-18 05:52:04

Currently "functional/hash - hash_float_test" fails on Tru64/CXX6.5 (See 
http://tinyurl.com/8opfo)

The reason of the failure is that QNaN and 0 give the same hash code on 
this platform. I was wondering what the expected hash of QNAN actually 
should be. Is it some platform dependent value?

I put some traces in hash_detail::float_hash_value(), and the cause for the 
same hash value for 0 and QNAN seems to be that static_cast<int>(QNAN) 
gives 0 which then results in a call of hash_combine(0, 0) for both 0 and QNAN.

Does anybody know what the expected result of static_cast<int>(QNAN) is? My 
guess is that either I should get a floating point exception for this 
expression or that the return value is unspecified and errno is set to 
[EDOM], but this is pure speculation on my side.

Markus