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 BatSetBatISet
Create an empty bitset of capacity 0, the bitset will automatically expand when needed.
Example: BitSet.empty ()
Create an empty bitset with at least an initial capacity (in number of bits).
Example: BitSet.create 0 = BitSet.empty ()
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
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 -> boolmem 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)
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.
These functions modify an existing bitset.
val set : t -> int -> unitset s n sets the nth-bit in the bitset s to true.
val unset : t -> int -> unitunset s n sets the nth-bit in the bitset s to false.
val put : t -> bool -> int -> unitput s v n sets the nth-bit in the bitset s to v.
val toggle : t -> int -> unittoggle s n changes the nth-bit value in the bitset s.
val intersect : t -> t -> intersect s t sets s to the intersection of the sets s and t.
val unite : t -> t -> unite s t sets s to the union of the sets s and t.
val differentiate : t -> t -> differentiate s t removes the elements of t from s.
val differentiate_sym : t -> t -> differentiate_sym s t sets s to the symmetrical difference of the sets s and t.
These functions return a new bitset that shares nothing with the input bitset. This is not as efficient as the in-place update.
add n s returns a copy of s with bit n true.
val remove : int -> t -> t remove n s returns a copy of s with bit n false.
inter s t returns the intersection of sets s and t.
union s t return the union of sets s and t.
val sym_diff : t -> t -> t sym_diff s t returns the symmetrical difference of s and t.
enum s returns an enumeration of bits which are set in the bitset s.
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 -> 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 -> equal s1 s2 returns true if, and only if, all bits values in s1 are the same as in s2.
ord s1 s2 returns BatOrd.Lt, BatOrd.Eq or BatOrd.Gt if compare s1 s2 is, respectively, < 0, 0 or > 0.
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.