expose GMP bit-flipping operations (tstbit, combit, etcetera)

[stevengj]

GMP provides some bit-fiddling operations that we don't currently export, e.g. to directly test or set the n-th bit.

You can simulate these operations by doing bit operations with BigInt(1) << n, but that requires constructing an intermediate BigInt.

Apparently these operations show up in some crypto algorithms, so it might be nice to expose a high-level interface.

[stevengj]

Note that in the short term it would also be perfectly reasonable for someone to create a package that simply exports and documents a bunch of low-level GMP functions.

[fatteneder]

A comparison with the methods form the link and what is/isn't available in Base.GMP.MPZ:

Not yet implemented:

• combit
• clrbit
• hamdist

Implemented, exported and documented:

• popcount via count_zeros/count_ones
• and/xor/ior/com as &, xor, |, ~
• scan0/scan1 via trailing_zeros/trailing_ones

Implemented, but unexported and undocumented:

• setbit!
• tstbit