BatBitSet
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
.
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 ()
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 -> 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)
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
.
These functions modify an existing bitset.
val set : t -> int -> unit
set s n
sets the n
th-bit in the bitset s
to true.
val unset : t -> int -> unit
unset s n
sets the n
th-bit in the bitset s
to false.
val put : t -> bool -> int -> unit
put s v n
sets the nth-bit in the bitset s
to v
.
val toggle : t -> int -> unit
toggle s n
changes the nth-bit value in the bitset s
.
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.
val print : 'a BatInnerIO.output -> t -> unit
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
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.
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
.