package batteries

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Efficient bit sets.

A bitset is an array of boolean values that can be accessed with indexes like an array but provides a better memory usage (divided by Sys.word_size; either 32 or 64) for a very small speed trade-off. It can provide efficient storage of dense sets of nonnegative integers near zero. Sparse sets should use BatSet, sets with large ranges of contiguous ints should use BatISet.

  • author Nicolas Cannasse
  • author David Teller (Boilerplate code)
type t
val empty : unit -> t

Create an empty bitset of capacity 0, the bitset will automatically expand when needed.

Example: BitSet.empty ()

val create : int -> t

Create an empty bitset with at least an initial capacity (in number of bits).

Example: BitSet.create 0 = BitSet.empty ()

  • raises Invalid_argument

    on negative capacity

val create_full : int -> t

Create a full bitset with at least initial capacity (in number of bits). All the bit under the defined capacity will be set.

Example: BitSet.count (BitSet.create_full n) = n

  • raises Invalid_argument

    on negative capacity

val copy : t -> t

Copy a bitset : further modifications of first one will not affect the copy.

Example: let a = Bitset.create 8 in let b = BitSet.copy a in BitSet.set a 6; BitSet.mem a 6 && not (BitSet.mem b 6)

val mem : t -> int -> bool

mem s n returns true if nth-bit in the bitset s is set, or false otherwise.

Example: let a = BitSet.create_full 256 in not (BitSet.mem a 300)

  • raises Invalid_argument

    on negative index (n < 0)

val count : t -> int

count s returns the number of bits set in the bitset s. Also known as Population Count, or cardinal for sets.

Example: BitSet.count (BitSet.of_list [6;4;2;2;1]) = 4

val next_set_bit : t -> int -> int option

next_set_bit s n returns Some m when m is the next set element with index greater than or equal n, or None if no such element exists (i.e. n is greater than the largest element)

More efficient than scanning with repeated BitSet.mem.

  • raises Invalid_argument

    on negative index (n < 0)

In-place Update

These functions modify an existing bitset.

val set : t -> int -> unit

set s n sets the nth-bit in the bitset s to true.

  • raises Invalid_argument

    on negative index (n < 0)

val unset : t -> int -> unit

unset s n sets the nth-bit in the bitset s to false.

  • raises Invalid_argument

    on negative index (n < 0)

val put : t -> bool -> int -> unit

put s v n sets the nth-bit in the bitset s to v.

  • raises Invalid_argument

    on negative index (n < 0)

val toggle : t -> int -> unit

toggle s n changes the nth-bit value in the bitset s.

  • raises Invalid_argument

    on negative index (n < 0)

val intersect : t -> t -> unit

intersect s t sets s to the intersection of the sets s and t.

val unite : t -> t -> unit

unite s t sets s to the union of the sets s and t.

val differentiate : t -> t -> unit

differentiate s t removes the elements of t from s.

val differentiate_sym : t -> t -> unit

differentiate_sym s t sets s to the symmetrical difference of the sets s and t.

Return new bitset

These functions return a new bitset that shares nothing with the input bitset. This is not as efficient as the in-place update.

val add : int -> t -> t

add n s returns a copy of s with bit n true.

  • raises Invalid_argument

    on negative index (n < 0)

val remove : int -> t -> t

remove n s returns a copy of s with bit n false.

  • raises Invalid_argument

    on negative index (n < 0)

val inter : t -> t -> t

inter s t returns the intersection of sets s and t.

val union : t -> t -> t

union s t return the union of sets s and t.

val diff : t -> t -> t

diff s t returns s-t.

val sym_diff : t -> t -> t

sym_diff s t returns the symmetrical difference of s and t.

Boilerplate code
val print : 'a BatInnerIO.output -> t -> unit
val enum : t -> int BatEnum.t

enum s returns an enumeration of bits which are set in the bitset s.

val of_enum : ?cap:int -> int BatEnum.t -> t

of_enum ~cap e builds a bitset of capacity cap an enumeration of ints e.

Note: Performance of this function may be poor if enumeration is in increasing order and the max.

val of_list : ?cap:int -> int list -> t

As of_enum, but from a list

val compare : t -> t -> int

compare s1 s2 compares two bitsets using a lexicographic ordering. Highest bit indexes are compared first. The capacity of the bitsets is not important for this comparison, only the bits starting with the highest set bit and going down.

val equal : t -> t -> bool

equal s1 s2 returns true if, and only if, all bits values in s1 are the same as in s2.

val ord : t -> t -> BatOrd.order

ord s1 s2 returns BatOrd.Lt, BatOrd.Eq or BatOrd.Gt if compare s1 s2 is, respectively, < 0, 0 or > 0.

val capacity : t -> int

Internals

capacity s returns the number of bits, both set and unset, stored in s. This is guaranteed to be larger than the largest element (set bit index) in s.