Support negative exponents in mul_2exp

[skirpichev]

• We try to convert to unsigned long (for mpfr_mul_2ui) and fallback to long on overflow (for mpfr_mul_2si), closes mul_2exp does not accept negative exponents #328
• Add GMPy_Integer_AsUnsignedLongOrLong() and adapt div_2exp() like above
• Return OverflowError in iroot(x,n) iff n>ULONG_MAX, closes TypeError in gmpy2.iroot #257

[codecov-commenter]

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All modified and coverable lines are covered by tests ✅

Comparison is base (e34324a) 85.05% compared to head (eee6f31) 85.35%.

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@@            Coverage Diff             @@
##           master     #458      +/-   ##
==========================================
+ Coverage   85.05%   85.35%   +0.29%     
==========================================
  Files          49       49              
  Lines       11733    11714      -19     
  Branches     2204     2204              
==========================================
+ Hits         9980     9998      +18     
+ Misses       1753     1716      -37     

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[skirpichev]

This does make sense for div_2exp() as well. But I'm thinking about some code reorganization first.

Maybe it does make sense to add some GMPy_Integer_As??? utility function, that try conversion to unsigned long and then to long?

[casevh]

This does make sense for div_2exp() as well. But I'm thinking about some code reorganization first.

Maybe it does make sense to add some GMPy_Integer_As??? utility function, that try conversion to unsigned long and then to long?

That would make sense. We need to include 64-bit values on Windows where long is only 32-bits. size_t and ssize_t could be used as the types.

[skirpichev]

That would make sense.

Is there any potential use cases besides div_2exp()?

[casevh]

Is there any potential use cases besides div_2exp()?

Those would be the most common. Almost any code that relies on bit positions or bit length could use size_t or ssize_t. See the bit indexing code in gmpy2_xmpz_misc.c for use of ssize_t.

[skirpichev]

@casevh, I think this is ready for review.

size_t and ssize_t could be used as the types.

I came to GMPy_Integer_AsUnsignedLongOrLong() helper function. GMP only has *_si/ui functions to work with signed/unsigned long.

[skirpichev]

CI failures are unrelated to this pr.

[casevh]

I came to GMPy_Integer_AsUnsignedLongOrLong() helper function. GMP only has *_si/ui functions to work with signed/unsigned long.

Agreed. Looks good. I'll merge it this weekend / when you tell me it is ready.

[skirpichev]

@casevh, it was mentioned above, that this pr is ready for review.

[skirpichev]

@casevh, I've added yet another (last, I think ;)) commit to this PR, which utilizes new function in iroot() (to raise OverflowError instead of ValueError's on overflow).

[casevh]

Thanks.