[issue8188] Unified hash for numeric types.

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

> Regarding a hash function for complex types, I think documenting the 
> existing behavior for PyComplex is sufficient. The magic number 1000003 > could be documented in hash_info as 'multiplier' and _PyHASH_MULTIPLIER. 

Seems reasonable;  I'm tempted to call the constant it hash_info.imaginary and _PyHASH_IMAGINARY, though.  :)  

There's also an implicit parameter in this algorithm, namely the size of a C long;  I think this should go into sys.hash_info, too.

complex_hash does need fixing in one respect:  it currently depends on signed overflow wrapping modulo 2**BIT_IN_LONG, but that's undefined behaviour;  it should use unsigned arithmetic instead.

> I think hash(m/P) should preserve sign. It just seems more symmetrical. :)

Agreed.  Along similar lines, I think I'm also going to get rid of _PyHASH_NINF and just use -PyHASH_INF instead.

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<http://bugs.python.org/issue8188>
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