[issue3166] Make conversions from long to float correctly rounded.

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

You may use "if (nbits == (size_t)-1 && PyErr_Occurred())" to check 
_PyLong_NumBits() error (overflow). Well, "if (numbits > DBL_MAX_EXP)" 
should already catch overflow, but I prefer explicit test to check the 
error case.

Anyway, interresting patch! Python3 vanilla:
>>> n = 295147905179352891391; int(float(n)) - n
-65535

Python3 + your patch:
>>> int(float(n)) - n
1

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stage:  -> patch review

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue3166>
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