Make BitSet store any Int #25029

The BitVector had already started to show its limits for BitSet needs. Juggling at 3 layers with BitSet, BitVector, and Vector{UInt64} was becoming confusing at times. Updating this code to handle negative integers only increased the confusion. Some modest performance improvements (~20%) could be achieved in the process for some functions.

Add an offset field to BitSet acting as an infimum of stored values, which can be adjusted on-the-fly. BitSet then becomes able to store negative integers, and doesn't have to have elements centered around 0.

The 1-based indexing was forcing to promote Int to Int128 in chk_indice & chk_offset, to allow correct computation with extreme values (e.g. BitSet([typemin(Int)])). 1-based indexing was a left-over from the former BitVector as underlying implementation. Switching to 0-based indexing allows both a more-direct mapping between the model and the implementation, and better performance.

When a BitSet is empty, its offset must be initialized. But checking for emptyness in each invocation of _setint! was costly, so we put the check in a branch which is called less often.

_setint! was delegating to the bitarray code, but then some work was being redone in get_chunks_id. So we split this functionality into lower level functions.

* isempty: using _check0 instead of all makes it 35% faster * ==: checking first non-overlapping parts is more likely to be faster, as the the lower and upper parts of the bits field are unlikely to be zero (at least for a freshly created BitSet)

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Make BitSet store any Int #25029

Make BitSet store any Int #25029

Commits on Dec 19, 2017