README.md
bitset
Go language library to map between non-negative integers and boolean values
This library is part of the awesome go collection. It is used in production by several important systems:
Description
Package bitset implements bitsets, a mapping between non-negative integers and boolean values. It should be more efficient than map[uint] bool.
It provides methods for setting, clearing, flipping, and testing individual integers.
But it also provides set intersection, union, difference, complement, and symmetric operations, as well as tests to check whether any, all, or no bits are set, and querying a bitset's current length and number of positive bits.
BitSets are expanded to the size of the largest set bit; the memory allocation is approximately Max bits, where Max is the largest set bit. BitSets are never shrunk. On creation, a hint can be given for the number of bits that will be used.
Many of the methods, including Set, Clear, and Flip, return a BitSet pointer, which allows for chaining.
Example use:
package main
import (
"fmt"
"math/rand"
"github.com/bits-and-blooms/bitset"
)
func main() {
fmt.Printf("Hello from BitSet!\n")
var b bitset.BitSet
// play some Go Fish
for i := 0; i < 100; i++ {
card1 := uint(rand.Intn(52))
card2 := uint(rand.Intn(52))
b.Set(card1)
if b.Test(card2) {
fmt.Println("Go Fish!")
}
b.Clear(card1)
}
// Chaining
b.Set(10).Set(11)
for i, e := b.NextSet(0); e; i, e = b.NextSet(i + 1) {
fmt.Println("The following bit is set:", i)
}
if b.Intersection(bitset.New(100).Set(10)).Count() == 1 {
fmt.Println("Intersection works.")
} else {
fmt.Println("Intersection doesn't work???")
}
}
Package documentation is at: https://pkg.go.dev/github.com/bits-and-blooms/bitset?tab=doc
Serialization
You may serialize a bitset safely and portably to a stream of bytes as follows:
const length = 9585
const oneEvery = 97
bs := bitset.New(length)
// Add some bits
for i := uint(0); i < length; i += oneEvery {
bs = bs.Set(i)
}
var buf bytes.Buffer
n, err := bs.WriteTo(&buf)
if err != nil {
// failure
}
// Here n == buf.Len()
You can later deserialize the result as follows:
// Read back from buf
bs = bitset.New()
n, err = bs.ReadFrom(&buf)
if err != nil {
// error
}
// n is the number of bytes read
The ReadFrom function attempts to read the data into the existing
BitSet instance, to minimize memory allocations.
Performance tip:
When reading and writing to a file or a network connection, you may get better performance by
wrapping your streams with bufio instances.
E.g.,
f, err := os.Create("myfile")
w := bufio.NewWriter(f)
f, err := os.Open("myfile")
r := bufio.NewReader(f)
Memory Usage
The memory usage of a bitset using N bits is at least N/8 bytes. The number of bits in a bitset is at least as large as one plus the greatest bit index you have accessed. Thus it is possible to run out of memory while using a bitset. If you have lots of bits, you might prefer compressed bitsets, like the Roaring bitmaps and its Go implementation.
The roaring library allows you to go back and forth between compressed Roaring bitmaps and the conventional bitset instances:
mybitset := roaringbitmap.ToBitSet()
newroaringbitmap := roaring.FromBitSet(mybitset)
Implementation Note
Go 1.9 introduced a native math/bits library. We provide backward compatibility to Go 1.7, which might be removed.
It is possible that a later version will match the math/bits return signature for counts (which is int, rather than our library's uint64). If so, the version will be bumped.
Installation
go get github.com/bits-and-blooms/bitset
Contributing
If you wish to contribute to this project, please branch and issue a pull request against master ("GitHub Flow")
Running all tests
Before committing the code, please check if it passes tests, has adequate coverage, etc.
go test
go test -cover