= Bits

Bits provides methods on a bit array type.

The Bits type holds a fixed size array of bits, numbered consecutively
from zero.  Some set-like operations are possible, but the API is more
array-like or register-like.

image:https://godoc.org/github.com/soniakeys/bits?status.svg[link=https://godoc.org/github.com/soniakeys/bits] image:https://travis-ci.org/soniakeys/bits.svg[link=https://travis-ci.org/soniakeys/bits]

== Motivation and history

This package evolved from needs of my library of
https://github.com/soniakeys/graph[graph algorithms].  For graph algorithms
a common need is to store a single bit of information per node in a way that
is both fast and memory efficient.  I began by using `big.Int` from the standard
library, then wrapped big.Int in a type.  From time to time I considered
other publicly available bit array or bit set packages, such as Will
Fitzgerald's popular https://github.com/willf/bitset[bitset], but there were
always little reasons I preferred my own type and methods.  My type that
wrapped `big.Int` met my needs until some simple benchmarks indicated it
might be causing performance problems.  Some further experiments supported
this hypothesis so I ran further tests with a prototype bit array written
from scratch.  Then satisfied that my custom bit array was solving the graph
performance problems, I decided to move it to a separate package with the
idea it might have more general utility.  For the initial version of this
package I did the following:

- implemented a few tests to demonstrate fundamental correctness
- brought over most methods of my type that wrapped big.Int
- changed the index type from the graph-specific node index to a general `int`
- replaced some custom bit-twiddling with use of the new `math/bits` package
  in the standard library
- renamed a few methods for clarity
- added a few methods for symmetry
- added a few new methods I had seen a need for in my graph library
- added doc, examples, tests, and more tests for 100% coverage
- added this readme