Documentation
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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 ¶
- func Base64StdEncoding()
- func Cap() uint
- func LittleEndian()
- type BitSet
- func (b *BitSet) All() bool
- func (b *BitSet) Any() bool
- func (b *BitSet) BinaryStorageSize() int
- func (b *BitSet) Bytes() []uint64
- func (b *BitSet) Clear(i uint) *BitSet
- func (b *BitSet) ClearAll() *BitSet
- func (b *BitSet) Clone() *BitSet
- func (b *BitSet) Compact() *BitSet
- func (b *BitSet) Complement() (result *BitSet)
- func (b *BitSet) Copy(c *BitSet) (count uint)
- func (b *BitSet) CopyFull(c *BitSet)
- func (b *BitSet) Count() uint
- func (b *BitSet) DeleteAt(i uint) *BitSet
- func (b *BitSet) Difference(compare *BitSet) (result *BitSet)
- func (b *BitSet) DifferenceCardinality(compare *BitSet) uint
- func (b *BitSet) DumpAsBits() string
- func (b *BitSet) Equal(c *BitSet) bool
- func (b *BitSet) Flip(i uint) *BitSet
- func (b *BitSet) FlipRange(start, end uint) *BitSet
- func (b *BitSet) InPlaceDifference(compare *BitSet)
- func (b *BitSet) InPlaceIntersection(compare *BitSet)
- func (b *BitSet) InPlaceSymmetricDifference(compare *BitSet)
- func (b *BitSet) InPlaceUnion(compare *BitSet)
- func (b *BitSet) InsertAt(idx uint) *BitSet
- func (b *BitSet) Intersection(compare *BitSet) (result *BitSet)
- func (b *BitSet) IntersectionCardinality(compare *BitSet) uint
- func (b *BitSet) IsStrictSuperSet(other *BitSet) bool
- func (b *BitSet) IsSuperSet(other *BitSet) bool
- func (b *BitSet) Len() uint
- func (b *BitSet) MarshalBinary() ([]byte, error)
- func (b *BitSet) MarshalJSON() ([]byte, error)
- func (b *BitSet) NextClear(i uint) (uint, bool)
- func (b *BitSet) NextSet(i uint) (uint, bool)
- func (b *BitSet) NextSetMany(i uint, buffer []uint) (uint, []uint)
- func (b *BitSet) None() bool
- func (b *BitSet) ReadFrom(stream io.Reader) (int64, error)
- func (b *BitSet) Set(i uint) *BitSet
- func (b *BitSet) SetBitsetFrom(buf []uint64)
- func (b *BitSet) SetTo(i uint, value bool) *BitSet
- func (b *BitSet) Shrink(lastbitindex uint) *BitSet
- func (b *BitSet) String() string
- func (b *BitSet) SymmetricDifference(compare *BitSet) (result *BitSet)
- func (b *BitSet) SymmetricDifferenceCardinality(compare *BitSet) uint
- func (b *BitSet) Test(i uint) bool
- func (b *BitSet) Union(compare *BitSet) (result *BitSet)
- func (b *BitSet) UnionCardinality(compare *BitSet) uint
- func (b *BitSet) UnmarshalBinary(data []byte) error
- func (b *BitSet) UnmarshalJSON(data []byte) error
- func (b *BitSet) WriteTo(stream io.Writer) (int64, error)
- type Error
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Base64StdEncoding ¶
func Base64StdEncoding()
Base64StdEncoding Marshal/Unmarshal BitSet with base64.StdEncoding(Default: base64.URLEncoding)
func LittleEndian ¶
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 FromWithLength ¶
FromWithLength constructs from an array of integers and length.
func (*BitSet) All ¶
All returns true if all bits are set, false otherwise. Returns true for empty sets.
func (*BitSet) BinaryStorageSize ¶
BinaryStorageSize returns the binary storage requirements
func (*BitSet) Compact ¶
Compact shrinks BitSet to so that we preserve all set bits, while minimizing memory usage. Compact calls Shrink.
func (*BitSet) Complement ¶
Complement computes the (local) complement of a biset (up to length bits)
func (*BitSet) Copy ¶
Copy into a destination BitSet using the Go array copy semantics: the number of bits copied is the minimum of the number of bits in the current BitSet (Len()) and the destination Bitset. We return the number of bits copied in the destination BitSet.
func (*BitSet) CopyFull ¶
CopyFull copies into a destination BitSet such that the destination is identical to the source after the operation, allocating memory if necessary.
func (*BitSet) DeleteAt ¶
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 ¶
Difference of base set and other set This is the BitSet equivalent of &^ (and not)
func (*BitSet) DifferenceCardinality ¶
DifferenceCardinality computes the cardinality of the differnce
func (*BitSet) DumpAsBits ¶
DumpAsBits dumps a bit set as a string of bits
func (*BitSet) Equal ¶
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 ¶
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) FlipRange ¶
FlipRange bit in [start, end). If end>= Cap(), this function will panic. Warning: using a very large value for 'end' 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 ¶
InPlaceDifference computes the difference of base set and other set This is the BitSet equivalent of &^ (and not)
func (*BitSet) InPlaceIntersection ¶
InPlaceIntersection destructively computes the intersection of base set and the compare set. This is the BitSet equivalent of & (and)
func (*BitSet) InPlaceSymmetricDifference ¶
InPlaceSymmetricDifference creates the destructive SymmetricDifference of base set and other set This is the BitSet equivalent of ^ (xor)
func (*BitSet) InPlaceUnion ¶
InPlaceUnion creates the destructive union of base set and compare set. This is the BitSet equivalent of | (or).
func (*BitSet) InsertAt ¶
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 ¶
Intersection of base set and other set This is the BitSet equivalent of & (and)
func (*BitSet) IntersectionCardinality ¶
IntersectionCardinality computes the cardinality of the union
func (*BitSet) IsStrictSuperSet ¶
IsStrictSuperSet returns true if this is a strict superset of the other set
func (*BitSet) IsSuperSet ¶
IsSuperSet returns true if this is a superset of the other set
func (*BitSet) Len ¶
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 ¶
MarshalBinary encodes a BitSet into a binary form and returns the result.
func (*BitSet) MarshalJSON ¶
MarshalJSON marshals a BitSet as a JSON structure
func (*BitSet) NextClear ¶
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 ¶
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 ¶
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 ¶
None returns true if no bit is set, false otherwise. Returns true for empty sets.
func (*BitSet) Set ¶
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) SetBitsetFrom ¶
SetBitsetFrom fills the bitset with an array of integers without creating a new BitSet instance
func (*BitSet) SetTo ¶
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 ¶
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) SymmetricDifference ¶
SymmetricDifference of base set and other set This is the BitSet equivalent of ^ (xor)
func (*BitSet) SymmetricDifferenceCardinality ¶
SymmetricDifferenceCardinality computes the cardinality of the symmetric difference
func (*BitSet) UnionCardinality ¶
UnionCardinality computes the cardinality of the uniton of the base set and the compare set.
func (*BitSet) UnmarshalBinary ¶
UnmarshalBinary decodes the binary form generated by MarshalBinary.
func (*BitSet) UnmarshalJSON ¶
UnmarshalJSON unmarshals a BitSet from JSON created using MarshalJSON
Source Files