bitset

package module
Version: v1.1.11 Latest Latest
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Published: Jul 30, 2020 License: BSD-3-Clause Imports: 10 Imported by: 0

README

bitset

Go language library to map between non-negative integers and boolean values

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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/willf/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???")
	}
}

As an alternative to BitSets, one should check out the 'big' package, which provides a (less set-theoretical) view of bitsets.

Package documentation is at: https://pkg.go.dev/github.com/willf/bitset?tab=doc

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.

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 unit64). If so, the version will be bumped.

Installation

go get github.com/willf/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

Documentation

Overview

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:

import "bitset"
var b BitSet
b.Set(10).Set(11)
if b.Test(1000) {
	b.Clear(1000)
}
if B.Intersection(bitset.New(100).Set(10)).Count() > 1 {
	fmt.Println("Intersection works.")
}

As an alternative to BitSets, one should check out the 'big' package, which provides a (less set-theoretical) view of bitsets.

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func Base64StdEncoding added in v1.1.4

func Base64StdEncoding()

Base64StdEncoding Marshal/Unmarshal BitSet with base64.StdEncoding(Default: base64.URLEncoding)

func Cap

func Cap() uint

Cap returns the total possible capacity, or number of bits

func LittleEndian added in v1.1.4

func LittleEndian()

LittleEndian Marshal/Unmarshal Binary as Little Endian(Default: binary.BigEndian)

Types

type BitSet

type BitSet struct {
	// contains filtered or unexported fields
}

A BitSet is a set of bits. The zero value of a BitSet is an empty set of length 0.

func From added in v1.1.2

func From(buf []uint64) *BitSet

From is a constructor used to create a BitSet from an array of integers

func New

func New(length uint) (bset *BitSet)

New creates a new BitSet with a hint that length bits will be required

func (*BitSet) All

func (b *BitSet) All() bool

All returns true if all bits are set, false otherwise. Returns true for empty sets.

func (*BitSet) Any

func (b *BitSet) Any() bool

Any returns true if any bit is set, false otherwise

func (*BitSet) BinaryStorageSize added in v1.1.2

func (b *BitSet) BinaryStorageSize() int

BinaryStorageSize returns the binary storage requirements

func (*BitSet) Bytes added in v1.1.2

func (b *BitSet) Bytes() []uint64

Bytes returns the bitset as array of integers

func (*BitSet) Clear

func (b *BitSet) Clear(i uint) *BitSet

Clear bit i to 0

func (*BitSet) ClearAll

func (b *BitSet) ClearAll() *BitSet

ClearAll clears the entire BitSet

func (*BitSet) Clone

func (b *BitSet) Clone() *BitSet

Clone this BitSet

func (*BitSet) Compact added in v1.1.11

func (b *BitSet) Compact() *BitSet

Compact shrinks BitSet to so that we preserve all set bits, while minimizing memory usage. Compact calls Shrink.

func (*BitSet) Complement

func (b *BitSet) Complement() (result *BitSet)

Complement computes the (local) complement of a biset (up to length bits)

func (*BitSet) Copy

func (b *BitSet) Copy(c *BitSet) (count uint)

Copy into a destination BitSet Returning the size of the destination BitSet like array copy

func (*BitSet) Count

func (b *BitSet) Count() uint

Count (number of set bits). Also known as "popcount" or "popularity count".

func (*BitSet) DeleteAt added in v1.1.10

func (b *BitSet) DeleteAt(i uint) *BitSet

DeleteAt deletes the bit at the given index position from within the bitset All the bits residing on the left of the deleted bit get shifted right by 1 The running time of this operation may potentially be relatively slow, O(length)

func (*BitSet) Difference

func (b *BitSet) Difference(compare *BitSet) (result *BitSet)

Difference of base set and other set This is the BitSet equivalent of &^ (and not)

func (*BitSet) DifferenceCardinality

func (b *BitSet) DifferenceCardinality(compare *BitSet) uint

DifferenceCardinality computes the cardinality of the differnce

func (*BitSet) DumpAsBits

func (b *BitSet) DumpAsBits() string

DumpAsBits dumps a bit set as a string of bits

func (*BitSet) Equal

func (b *BitSet) Equal(c *BitSet) bool

Equal tests the equivalence of two BitSets. False if they are of different sizes, otherwise true only if all the same bits are set

func (*BitSet) Flip

func (b *BitSet) Flip(i uint) *BitSet

Flip bit at i. If i>= Cap(), this function will panic. Warning: using a very large value for 'i' may lead to a memory shortage and a panic: the caller is responsible for providing sensible parameters in line with their memory capacity.

func (*BitSet) InPlaceDifference

func (b *BitSet) InPlaceDifference(compare *BitSet)

InPlaceDifference computes the difference of base set and other set This is the BitSet equivalent of &^ (and not)

func (*BitSet) InPlaceIntersection

func (b *BitSet) InPlaceIntersection(compare *BitSet)

InPlaceIntersection destructively computes the intersection of base set and the compare set. This is the BitSet equivalent of & (and)

func (*BitSet) InPlaceSymmetricDifference

func (b *BitSet) InPlaceSymmetricDifference(compare *BitSet)

InPlaceSymmetricDifference creates the destructive SymmetricDifference of base set and other set This is the BitSet equivalent of ^ (xor)

func (*BitSet) InPlaceUnion

func (b *BitSet) InPlaceUnion(compare *BitSet)

InPlaceUnion creates the destructive union of base set and compare set. This is the BitSet equivalent of | (or).

func (*BitSet) InsertAt added in v1.1.10

func (b *BitSet) InsertAt(idx uint) *BitSet

InsertAt takes an index which indicates where a bit should be inserted. Then it shifts all the bits in the set to the left by 1, starting from the given index position, and sets the index position to 0.

Depending on the size of your BitSet, and where you are inserting the new entry, this method could be extremely slow and in some cases might cause the entire BitSet to be recopied.

func (*BitSet) Intersection

func (b *BitSet) Intersection(compare *BitSet) (result *BitSet)

Intersection of base set and other set This is the BitSet equivalent of & (and)

func (*BitSet) IntersectionCardinality

func (b *BitSet) IntersectionCardinality(compare *BitSet) uint

IntersectionCardinality computes the cardinality of the union

func (*BitSet) IsStrictSuperSet added in v1.1.2

func (b *BitSet) IsStrictSuperSet(other *BitSet) bool

IsStrictSuperSet returns true if this is a strict superset of the other set

func (*BitSet) IsSuperSet added in v1.1.2

func (b *BitSet) IsSuperSet(other *BitSet) bool

IsSuperSet returns true if this is a superset of the other set

func (*BitSet) Len

func (b *BitSet) Len() uint

Len returns the number of bits in the BitSet. Note the difference to method Count, see example.

Example
var b BitSet
b.Set(8)
fmt.Println("len", b.Len())
fmt.Println("count", b.Count())
Output:

len 9
count 1

func (*BitSet) MarshalBinary added in v1.1.2

func (b *BitSet) MarshalBinary() ([]byte, error)

MarshalBinary encodes a BitSet into a binary form and returns the result.

func (*BitSet) MarshalJSON

func (b *BitSet) MarshalJSON() ([]byte, error)

MarshalJSON marshals a BitSet as a JSON structure

func (*BitSet) NextClear added in v1.1.2

func (b *BitSet) NextClear(i uint) (uint, bool)

NextClear returns the next clear bit from the specified index, including possibly the current index along with an error code (true = valid, false = no bit found i.e. all bits are set)

func (*BitSet) NextSet

func (b *BitSet) NextSet(i uint) (uint, bool)

NextSet returns the next bit set from the specified index, including possibly the current index along with an error code (true = valid, false = no set bit found) for i,e := v.NextSet(0); e; i,e = v.NextSet(i + 1) {...}

Users concerned with performance may want to use NextSetMany to retrieve several values at once.

func (*BitSet) NextSetMany added in v1.1.4

func (b *BitSet) NextSetMany(i uint, buffer []uint) (uint, []uint)

NextSetMany returns many next bit sets from the specified index, including possibly the current index and up to cap(buffer). If the returned slice has len zero, then no more set bits were found

buffer := make([]uint, 256) // this should be reused
j := uint(0)
j, buffer = bitmap.NextSetMany(j, buffer)
for ; len(buffer) > 0; j, buffer = bitmap.NextSetMany(j,buffer) {
 for k := range buffer {
  do something with buffer[k]
 }
 j += 1
}

It is possible to retrieve all set bits as follow:

indices := make([]uint, bitmap.Count())
bitmap.NextSetMany(0, indices)

However if bitmap.Count() is large, it might be preferable to use several calls to NextSetMany, for performance reasons.

func (*BitSet) None

func (b *BitSet) None() bool

None returns true if no bit is set, false otherwise. Returns true for empty sets.

func (*BitSet) ReadFrom added in v1.1.2

func (b *BitSet) ReadFrom(stream io.Reader) (int64, error)

ReadFrom reads a BitSet from a stream written using WriteTo

func (*BitSet) Set

func (b *BitSet) Set(i uint) *BitSet

Set bit i to 1, the capacity of the bitset is automatically increased accordingly. If i>= Cap(), this function will panic. Warning: using a very large value for 'i' may lead to a memory shortage and a panic: the caller is responsible for providing sensible parameters in line with their memory capacity.

func (*BitSet) SetTo

func (b *BitSet) SetTo(i uint, value bool) *BitSet

SetTo sets bit i to value. If i>= Cap(), this function will panic. Warning: using a very large value for 'i' may lead to a memory shortage and a panic: the caller is responsible for providing sensible parameters in line with their memory capacity.

func (*BitSet) Shrink added in v1.1.10

func (b *BitSet) Shrink(lastbitindex uint) *BitSet

Shrink shrinks BitSet so that the provided value is the last possible set value. It clears all bits > the provided index and reduces the size and length of the set.

Note that the parameter value is not the new length in bits: it is the maximal value that can be stored in the bitset after the function call. The new length in bits is the parameter value + 1. Thus it is not possible to use this function to set the length to 0, the minimal value of the length after this function call is 1.

A new slice is allocated to store the new bits, so you may see an increase in memory usage until the GC runs. Normally this should not be a problem, but if you have an extremely large BitSet its important to understand that the old BitSet will remain in memory until the GC frees it.

func (*BitSet) String added in v1.1.2

func (b *BitSet) String() string

String creates a string representation of the Bitmap

func (*BitSet) SymmetricDifference

func (b *BitSet) SymmetricDifference(compare *BitSet) (result *BitSet)

SymmetricDifference of base set and other set This is the BitSet equivalent of ^ (xor)

func (*BitSet) SymmetricDifferenceCardinality

func (b *BitSet) SymmetricDifferenceCardinality(compare *BitSet) uint

SymmetricDifferenceCardinality computes the cardinality of the symmetric difference

func (*BitSet) Test

func (b *BitSet) Test(i uint) bool

Test whether bit i is set.

func (*BitSet) Union

func (b *BitSet) Union(compare *BitSet) (result *BitSet)

Union of base set and other set This is the BitSet equivalent of | (or)

func (*BitSet) UnionCardinality

func (b *BitSet) UnionCardinality(compare *BitSet) uint

UnionCardinality computes the cardinality of the uniton of the base set and the compare set.

func (*BitSet) UnmarshalBinary added in v1.1.2

func (b *BitSet) UnmarshalBinary(data []byte) error

UnmarshalBinary decodes the binary form generated by MarshalBinary.

func (*BitSet) UnmarshalJSON

func (b *BitSet) UnmarshalJSON(data []byte) error

UnmarshalJSON unmarshals a BitSet from JSON created using MarshalJSON

func (*BitSet) WriteTo added in v1.1.2

func (b *BitSet) WriteTo(stream io.Writer) (int64, error)

WriteTo writes a BitSet to a stream

type Error added in v1.1.2

type Error string

Error is used to distinguish errors (panics) generated in this package.

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