package bitv

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package bitv
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This module implements bit vectors, as an abstract datatype t. Since bit vectors are particular cases of arrays, this module provides the same operations as module Array. It also provides bitwise operations and conversions to/from integer types.

In the following, false stands for bit 0 and true for bit 1.

type t

the type of bit vectors

Creation, access and assignment.

val create : int -> bool -> t

(Bitv.create n b) creates a new bit vector of length n, initialized with b.

val init : int -> (int -> bool) -> t

(Bitv.init n f) returns a fresh vector of length n, with bit number i initialized to the result of (f i).

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

(Bitv.set v n b) sets the nth bit of v to the value b.

val get : t -> int -> bool

(Bitv.get v n) returns the nth bit of v.

val length : t -> int

Bitv.length returns the length (number of elements) of the given vector.

val equal : t -> t -> bool

Returns true if two bit vectors are of the same length and with the same bits.

val tanimoto : t -> t -> float

Bitv.tanimoto v1 v2 is |inter(v1,v2)| / |union(v1,v2)|. Also called the Jaccard score. (1 - tanimoto) is a proper distance. raises Invalid_argument if the two vectors do not have the same length

val max_length : int
  • deprecated

    Use exceeds_max_length instead. On a 32-bit platform (e.g. Javascript) the computation of max_length may overflow and return a negative value.

val exceeds_max_length : int -> bool

Returns true if the argument exceeds the maximum length of a bit vector (System dependent).

Copies and concatenations.

val copy : t -> t

(Bitv.copy v) returns a copy of v, that is, a fresh vector containing the same elements as v.

val append : t -> t -> t

(Bitv.append v1 v2) returns a fresh vector containing the concatenation of the vectors v1 and v2.

val concat : t list -> t

Bitv.concat is similar to Bitv.append, but catenates a list of vectors.

Sub-vectors and filling.

val sub : t -> int -> int -> t

(Bitv.sub v start len) returns a fresh vector of length len, containing the bits number start to start + len - 1 of vector v. Raise Invalid_argument "Bitv.sub" if start and len do not designate a valid subvector of v; that is, if start < 0, or len < 0, or start + len > Bitv.length a.

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

(Bitv.fill v ofs len b) modifies the vector v in place, storing b in elements number ofs to ofs + len - 1. Raise Invalid_argument "Bitv.fill" if ofs and len do not designate a valid subvector of v.

val blit : t -> int -> t -> int -> int -> unit

(Bitv.blit v1 o1 v2 o2 len) copies len elements from vector v1, starting at element number o1, to vector v2, starting at element number o2. It does not work correctly if v1 and v2 are the same vector with the source and destination chunks overlapping. Raise Invalid_argument "Bitv.blit" if o1 and len do not designate a valid subvector of v1, or if o2 and len do not designate a valid subvector of v2.

Iterators

val iter : (bool -> unit) -> t -> unit

(Bitv.iter f v) applies function f in turn to all the elements of v.

val map : (bool -> bool) -> t -> t

Given a function f, (Bitv.map f v) applies f to all the elements of v, and builds a vector with the results returned by f.

val iteri : (int -> bool -> unit) -> t -> unit
val mapi : (int -> bool -> bool) -> t -> t

Bitv.iteri and Bitv.mapi are similar to Bitv.iter and Bitv.map respectively, but the function is applied to the index of the element as first argument, and the element itself as second argument.

val fold_left : ('a -> bool -> 'a) -> 'a -> t -> 'a

(Bitv.fold_left f x v) computes f (... (f (f x (get v 0)) (get v 1)) ...) (get v (n-1)), where n is the length of the vector v.

val fold_right : (bool -> 'a -> 'a) -> t -> 'a -> 'a

(Bitv.fold_right f a x) computes f (get v 0) (f (get v 1) ( ... (f (get v (n-1)) x) ...)), where n is the length of the vector v.

val foldi_left : ('a -> int -> bool -> 'a) -> 'a -> t -> 'a
val foldi_right : (int -> bool -> 'a -> 'a) -> t -> 'a -> 'a

Pop count and other iterations

val pop : t -> int

Population count, i.e., number of 1 bits

val iteri_true : (int -> unit) -> t -> unit

iteri_true f v applies function f in turn to all indexes of the elements of v which are set (i.e. true); indexes are visited from least significant to most significant.

val gray_iter : (t -> unit) -> int -> unit

gray_iter f n iterates function f on all bit vectors of length n, once each, using a Gray code. The order in which bit vectors are processed is unspecified.

Bitwise operations.

All the bitwise operations return fresh vectors.

val bw_and : t -> t -> t

bitwise AND; raises Invalid_argument if the two vectors do not have the same length

val bw_or : t -> t -> t

bitwise OR; raises Invalid_argument if the two vectors do not have the same length

val bw_xor : t -> t -> t

bitwise XOR; raises Invalid_argument if the two vectors do not have the same length

val bw_not : t -> t

bitwise NOT

val shiftl : t -> int -> t

moves bits from least to most significant; introduces zeros

val shiftr : t -> int -> t

moves bits from most to least significant; introduces zeros

val rotatel : t -> int -> t

moves bits from least to most significant with wraparound

val rotater : t -> int -> t

moves bits from most to least significant with wraparound

Test functions

val all_zeros : t -> bool

returns true if and only if the vector only contains zeros

val all_ones : t -> bool

returns true if and only if the vector only contains ones

Conversions to and from strings

module L : sig ... end

With least significant bits first.

module M : sig ... end

With most significant bits first.

Input/output in a machine-independent format

The following functions export/import a bit vector to/from a channel or bytes, in a way that is compact, independent of the machine architecture, and independent of the OCaml version. For a bit vector of length n, the number of bytes of this external representation is 8+ceil(n/8).

val output_bin : Pervasives.out_channel -> t -> unit
val input_bin : Pervasives.in_channel -> t
val to_bytes : t -> bytes
val of_bytes : bytes -> t

Conversions to and from lists of integers

The list gives the indices of bits which are set (i.e. true).

val to_list : t -> int list
val of_list : int list -> t
val of_list_with_length : int list -> int -> t

Interpretation of bit vectors as integers

Least significant bit comes first (ie is at index 0 in the bit vector). to_xxx functions truncate when the bit vector is too wide. Suffix _s means that sign bit is kept, and _us that it is discarded.

type int (length 31/63 with sign, 30/62 without)

val of_int_s : int -> t
val to_int_s : t -> int
val of_int_us : int -> t
val to_int_us : t -> int

type Int32.t (length 32 with sign, 31 without)

val of_int32_s : Int32.t -> t
val to_int32_s : t -> Int32.t
val of_int32_us : Int32.t -> t
val to_int32_us : t -> Int32.t

type Int64.t (length 64 with sign, 63 without)

val of_int64_s : Int64.t -> t
val to_int64_s : t -> Int64.t
val of_int64_us : Int64.t -> t
val to_int64_us : t -> Int64.t

type Nativeint.t (length 32/64 with sign, 31/63 without)

val of_nativeint_s : Nativeint.t -> t
val to_nativeint_s : t -> Nativeint.t
val of_nativeint_us : Nativeint.t -> t
val to_nativeint_us : t -> Nativeint.t

Only if you know what you are doing...

val unsafe_set : t -> int -> bool -> unit
val unsafe_get : t -> int -> bool
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