Random hash_value for mpfr_float(0)

[fintarin]

The hash_value for mpfr_float constructed from zero int is random. Thus, hash_value(mpfr_float(0)) != hash_value(mpfr_float(0)). The problem is related to data()[0]._mpfr_d - code.

When debugging hash_function(mpfr_float(0)) I get various random _mpfr_d such as:

• {0,8461470348308866388,7019261819594830956,7163369272283972460,8391161944126416233,8031153322401625088,8021807474101977202,8319401290704975468,7146776104407163694}
• {0,7308619195232122478,7954879178731648110,7598805559586157151,3414698781512329070,3417225383054243439,8021807474102005619,8319401290704975468,7146776104407163694}

I assume that _mpfr_d holds an uninitialised values when the number is initialised with zero. So to fix this, you should check is_zero in the hash_value function. Also, the same problem can occur with other special values such as infinity and nan.