Add iterator starting at a given value

[michaelmior]

This is a follow up to #53 which implements next_set_biton top of an iterator for equal or larger. I'm not sure I'm happy with the naming and I expect the implementation may need some tweaks, but it works :)

[Ezibenroc]

Thank you, great PR!

Correct me if I am wrong, but I think that you can already achieve a similar thing with the rank() method and slices:

bm = BitMap(range(0, 100, 3))
for i in range(1, 100):
    assert list(bm[bm.rank(i-1):]) == list(bm.iter_equal_or_larger(i))
    assert bm[bm.rank(i-1)] == bm.next_set_bit(i)

So, the main benefits of these new methods are:

• Only one search in the bitmap instead of two
• Lazy evaluation with the iterator for iter_equal_or_larger, so more efficient if we do not need all the values (but if we do need all the values as a bitmap, the rank() solution is probably much better).

In my first (quick) tests, it seems great for next_set_bit:

bm = BitMap(range(0, 100000000, 3))

%timeit bm[bm.rank(1234567-1)]
4.88 µs ± 43.7 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

%timeit bm.next_set_bit(1234567)
482 ns ± 2.67 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

For iter_equal_or_larger, I do not think there is a fair comparison possible.

---

Before I merge, could you add some documentation for iter_equal_or_larger?

[michaelmior]

@Ezibenroc Good point that this could be done with rank and thanks for the benchmark! I added the extra documentation.

[Ezibenroc]

Thanks!

[michaelmior]

Thanks for the merge!