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=============

This is a go port of the Roaring bitmap data structure.

Roaring is  used by [Apache Spark](https://spark.apache.org/), [Apache Kylin](http://kylin.io),  [Netflix Atlas](https://github.com/Netflix/atlas), [LinkedIn Pinot](https://github.com/linkedin/pinot/wiki), [Druid.io](http://druid.io/), [Whoosh](https://pypi.python.org/pypi/Whoosh/), [Pilosa](https://www.pilosa.com/),
and  [Apache Lucene](http://lucene.apache.org/) (as well as supporting systems
such as Solr and Elastic).

Roaring bitmaps are found to work well in many important applications:

> Use Roaring for bitmap compression whenever possible. Do not use other bitmap compression methods ([Wang et al., SIGMOD 2017](http://db.ucsd.edu/wp-content/uploads/2017/03/sidm338-wangA.pdf))


The ``roaring`` Go library is used by
* [Cloud Torrent](https://github.com/jpillora/cloud-torrent): a self-hosted remote torrent client
* [runv](https://github.com/hyperhq/runv): an Hypervisor-based runtime for the Open Containers Initiative

There are also  [Java](https://github.com/RoaringBitmap/RoaringBitmap) and [C/C++](https://github.com/RoaringBitmap/CRoaring) versions.  The Java, C, C++ and Go version are binary compatible: e.g,  you can save bitmaps
from a Java program and load them back in Go, and vice versa. We have a [format specification](https://github.com/RoaringBitmap/RoaringFormatSpec).


This code is licensed under Apache License, Version 2.0 (ASL2.0).

Copyright 2016 by the authors.


### References

-  Samy Chambi, Daniel Lemire, Owen Kaser, Robert Godin,
Better bitmap performance with Roaring bitmaps,
Software: Practice and Experience Volume 46, Issue 5, pages 709–719, May 2016
http://arxiv.org/abs/1402.6407 This paper used data from http://lemire.me/data/realroaring2014.html
- Daniel Lemire, Gregory Ssi-Yan-Kai, Owen Kaser, Consistently faster and smaller compressed bitmaps with Roaring, Software: Practice and Experience (accepted in 2016, to appear) http://arxiv.org/abs/1603.06549


### Dependencies

Dependencies are fetched automatically by giving the `-t` flag to `go get`.

they include

  - github.com/smartystreets/goconvey/convey
  - github.com/willf/bitset
  - github.com/mschoch/smat

Note that the smat library requires Go 1.6 or better.

#### Installation

  - go get -t github.com/RoaringBitmap/roaring


### Example

Here is a simplified but complete example:

```go
package main

import (
    "fmt"
    "github.com/RoaringBitmap/roaring"
    "bytes"
)


func main() {
    // example inspired by https://github.com/fzandona/goroar
    fmt.Println("==roaring==")
    rb1 := roaring.BitmapOf(1, 2, 3, 4, 5, 100, 1000)
    fmt.Println(rb1.String())

    rb2 := roaring.BitmapOf(3, 4, 1000)
    fmt.Println(rb2.String())

    rb3 := roaring.NewBitmap()
    fmt.Println(rb3.String())

    fmt.Println("Cardinality: ", rb1.GetCardinality())

    fmt.Println("Contains 3? ", rb1.Contains(3))

    rb1.And(rb2)

    rb3.Add(1)
    rb3.Add(5)

    rb3.Or(rb1)

    // prints 1, 3, 4, 5, 1000
    i := rb3.Iterator()
    for i.HasNext() {
        fmt.Println(i.Next())
    }
    fmt.Println()

    // next we include an example of serialization
    buf := new(bytes.Buffer)
    rb1.WriteTo(buf) // we omit error handling
    newrb:= roaring.NewBitmap()
    newrb.ReadFrom(buf)
    if rb1.Equals(newrb) {
    	fmt.Println("I wrote the content to a byte stream and read it back.")
    }
}
```

If you wish to use serialization and handle errors, you might want to
consider the following sample of code:

```go
	rb := BitmapOf(1, 2, 3, 4, 5, 100, 1000)
	buf := new(bytes.Buffer)
	size,err:=rb.WriteTo(buf)
	if err != nil {
		t.Errorf("Failed writing")
	}
	newrb:= NewBitmap()
	size,err=newrb.ReadFrom(buf)
	if err != nil {
		t.Errorf("Failed reading")
	}
	if ! rb.Equals(newrb) {
		t.Errorf("Cannot retrieve serialized version")
	}
```

Given N integers in [0,x), then the serialized size in bytes of
a Roaring bitmap should never exceed this bound:

`` 8 + 9 * ((long)x+65535)/65536 + 2 * N ``

That is, given a fixed overhead for the universe size (x), Roaring
bitmaps never use more than 2 bytes per integer. You can call
``BoundSerializedSizeInBytes`` for a more precise estimate.


### Documentation

Current documentation is available at http://godoc.org/github.com/RoaringBitmap/roaring

### Goroutine safety

In general, it should not generally be considered safe to access
the same bitmaps using different goroutines--they are left
unsynchronized for performance. Should you want to access
a Bitmap from more than one goroutine, you should
provide synchronization. Typically this is done by using channels to pass
the *Bitmap around (in Go style; so there is only ever one owner),
or by using `sync.Mutex` to serialize operations on Bitmaps.

### Coverage

We test our software. For a report on our test coverage, see

https://coveralls.io/github/RoaringBitmap/roaring?branch=master

### Benchmark

Type

         go test -bench Benchmark -run -

### Iterative use

You can use roaring with gore:

- go get -u github.com/motemen/gore
- Make sure that ``$GOPATH/bin`` is in your ``$PATH``.
- go get github/RoaringBitmap/roaring

```go
$ gore
gore version 0.2.6  :help for help
gore> :import github.com/RoaringBitmap/roaring
gore> x:=roaring.New()
gore> x.Add(1)
gore> x.String()
"{1}"
```


### Fuzzy testing

You can help us test further the library with fuzzy testing:

         go get github.com/dvyukov/go-fuzz/go-fuzz
         go get github.com/dvyukov/go-fuzz/go-fuzz-build
         go test -tags=gofuzz -run=TestGenerateSmatCorpus
         go-fuzz-build github.com/RoaringBitmap/roaring
         go-fuzz -bin=./roaring-fuzz.zip -workdir=workdir/ -timeout=200

Let it run, and if the # of crashers is > 0, check out the reports in
the workdir where you should be able to find the panic goroutine stack
traces.

### Alternative in Go

There is a Go version wrapping the C/C++ implementation https://github.com/RoaringBitmap/gocroaring

For an alternative implementation in Go, see https://github.com/fzandona/goroar
The two versions were written independently.


### Mailing list/discussion group

https://groups.google.com/forum/#!forum/roaring-bitmaps
