oracular (3) Float.Array.3o.gz
NAME
Float.Array - Float arrays with packed representation.
Module
Module Float.Array
Documentation
Module Array
: sig end
Float arrays with packed representation.
type t = floatarray
The type of float arrays with packed representation.
Since 4.08
val length : t -> int
Return the length (number of elements) of the given floatarray.
val get : t -> int -> float
get a n returns the element number n of floatarray a .
Raises Invalid_argument if n is outside the range 0 to (length a - 1) .
val set : t -> int -> float -> unit
set a n x modifies floatarray a in place, replacing element number n with x .
Raises Invalid_argument if n is outside the range 0 to (length a - 1) .
val make : int -> float -> t
make n x returns a fresh floatarray of length n , initialized with x .
Raises Invalid_argument if n < 0 or n > Sys.max_floatarray_length .
val create : int -> t
create n returns a fresh floatarray of length n , with uninitialized data.
Raises Invalid_argument if n < 0 or n > Sys.max_floatarray_length .
val init : int -> (int -> float) -> t
init n f returns a fresh floatarray of length n , with element number i initialized to the result of f i
. In other terms, init n f tabulates the results of f applied to the integers 0 to n-1 .
Raises Invalid_argument if n < 0 or n > Sys.max_floatarray_length .
val make_matrix : int -> int -> float -> t array
make_matrix dimx dimy e returns a two-dimensional array (an array of arrays) with first dimension dimx
and second dimension dimy , where all elements are initialized with e .
Since 5.2
Raises Invalid_argument if dimx or dimy is negative or greater than Sys.max_floatarray_length .
val init_matrix : int -> int -> (int -> int -> float) -> t array
init_matrix dimx dimy f returns a two-dimensional array (an array of arrays) with first dimension dimx
and second dimension dimy , where the element at index ( x,y ) is initialized with f x y .
Since 5.2
Raises Invalid_argument if dimx or dimy is negative or greater than Sys.max_floatarray_length .
val append : t -> t -> t
append v1 v2 returns a fresh floatarray containing the concatenation of the floatarrays v1 and v2 .
Raises Invalid_argument if length v1 + length v2 > Sys.max_floatarray_length .
val concat : t list -> t
Same as Float.Array.append , but concatenates a list of floatarrays.
val sub : t -> int -> int -> t
sub a pos len returns a fresh floatarray of length len , containing the elements number pos to pos + len
- 1 of floatarray a .
Raises Invalid_argument if pos and len do not designate a valid subarray of a ; that is, if pos < 0 , or
len < 0 , or pos + len > length a .
val copy : t -> t
copy a returns a copy of a , that is, a fresh floatarray containing the same elements as a .
val fill : t -> int -> int -> float -> unit
fill a pos len x modifies the floatarray a in place, storing x in elements number pos to pos + len - 1 .
Raises Invalid_argument if pos and len do not designate a valid subarray of a .
val blit : t -> int -> t -> int -> int -> unit
blit src src_pos dst dst_pos len copies len elements from floatarray src , starting at element number
src_pos , to floatarray dst , starting at element number dst_pos . It works correctly even if src and
dst are the same floatarray, and the source and destination chunks overlap.
Raises Invalid_argument if src_pos and len do not designate a valid subarray of src , or if dst_pos and
len do not designate a valid subarray of dst .
val to_list : t -> float list
to_list a returns the list of all the elements of a .
val of_list : float list -> t
of_list l returns a fresh floatarray containing the elements of l .
Raises Invalid_argument if the length of l is greater than Sys.max_floatarray_length .
Iterators
val iter : (float -> unit) -> t -> unit
iter f a applies function f in turn to all the elements of a . It is equivalent to f a.(0); f a.(1);
...; f a.(length a - 1); () .
val iteri : (int -> float -> unit) -> t -> unit
Same as Float.Array.iter , but the function is applied with the index of the element as first argument,
and the element itself as second argument.
val map : (float -> float) -> t -> t
map f a applies function f to all the elements of a , and builds a floatarray with the results returned
by f .
val map_inplace : (float -> float) -> t -> unit
map_inplace f a applies function f to all elements of a , and updates their values in place.
Since 5.1
val mapi : (int -> float -> float) -> t -> t
Same as Float.Array.map , but the function is applied to the index of the element as first argument, and
the element itself as second argument.
val mapi_inplace : (int -> float -> float) -> t -> unit
Same as Float.Array.map_inplace , but the function is applied to the index of the element as first
argument, and the element itself as second argument.
Since 5.1
val fold_left : ('acc -> float -> 'acc) -> 'acc -> t -> 'acc
fold_left f x init computes f (... (f (f x init.(0)) init.(1)) ...) init.(n-1) , where n is the length of
the floatarray init .
val fold_right : (float -> 'acc -> 'acc) -> t -> 'acc -> 'acc
fold_right f a init computes f a.(0) (f a.(1) ( ... (f a.(n-1) init) ...)) , where n is the length of
the floatarray a .
Iterators on two arrays
val iter2 : (float -> float -> unit) -> t -> t -> unit
Array.iter2 f a b applies function f to all the elements of a and b .
Raises Invalid_argument if the floatarrays are not the same size.
val map2 : (float -> float -> float) -> t -> t -> t
map2 f a b applies function f to all the elements of a and b , and builds a floatarray with the results
returned by f : [| f a.(0) b.(0); ...; f a.(length a - 1) b.(length b - 1)|] .
Raises Invalid_argument if the floatarrays are not the same size.
Array scanning
val for_all : (float -> bool) -> t -> bool
for_all f [|a1; ...; an|] checks if all elements of the floatarray satisfy the predicate f . That is, it
returns (f a1) && (f a2) && ... && (f an) .
val exists : (float -> bool) -> t -> bool
exists f [|a1; ...; an|] checks if at least one element of the floatarray satisfies the predicate f .
That is, it returns (f a1) || (f a2) || ... || (f an) .
val mem : float -> t -> bool
mem a set is true if and only if there is an element of set that is structurally equal to a , i.e. there
is an x in set such that compare a x = 0 .
val mem_ieee : float -> t -> bool
Same as Float.Array.mem , but uses IEEE equality instead of structural equality.
Array searching
val find_opt : (float -> bool) -> t -> float option
val find_index : (float -> bool) -> t -> int option
find_index f a returns Some i , where i is the index of the first element of the array a that satisfies f
x , if there is such an element.
It returns None if there is no such element.
Since 5.1
val find_map : (float -> 'a option) -> t -> 'a option
val find_mapi : (int -> float -> 'a option) -> t -> 'a option
Same as find_map , but the predicate is applied to the index of the element as first argument (counting
from 0), and the element itself as second argument.
Since 5.1
Sorting and shuffling
val sort : (float -> float -> int) -> t -> unit
Sort a floatarray in increasing order according to a comparison function. The comparison function must
return 0 if its arguments compare as equal, a positive integer if the first is greater, and a negative
integer if the first is smaller (see below for a complete specification). For example, compare is a
suitable comparison function. After calling sort , the array is sorted in place in increasing order.
sort is guaranteed to run in constant heap space and (at most) logarithmic stack space.
The current implementation uses Heap Sort. It runs in constant stack space.
Specification of the comparison function: Let a be the floatarray and cmp the comparison function. The
following must be true for all x , y , z in a :
- cmp x y > 0 if and only if cmp y x < 0
- if cmp x y >= 0 and cmp y z >= 0 then cmp x z >= 0
When sort returns, a contains the same elements as before, reordered in such a way that for all i and j
valid indices of a :
- cmp a.(i) a.(j) >= 0 if and only if i >= j
val stable_sort : (float -> float -> int) -> t -> unit
Same as Float.Array.sort , but the sorting algorithm is stable (i.e. elements that compare equal are
kept in their original order) and not guaranteed to run in constant heap space.
The current implementation uses Merge Sort. It uses a temporary floatarray of length n/2 , where n is the
length of the floatarray. It is usually faster than the current implementation of Float.Array.sort .
val fast_sort : (float -> float -> int) -> t -> unit
Same as Float.Array.sort or Float.Array.stable_sort , whichever is faster on typical input.
val shuffle : rand:(int -> int) -> t -> unit
shuffle rand a randomly permutes a 's elements using rand for randomness. The distribution of
permutations is uniform.
rand must be such that a call to rand n returns a uniformly distributed random number in the range [ 0 ;
n-1 ]. Random.int can be used for this (do not forget to Random.self_init the generator).
Since 5.2
Float arrays and Sequences
val to_seq : t -> float Seq.t
Iterate on the floatarray, in increasing order. Modifications of the floatarray during iteration will be
reflected in the sequence.
val to_seqi : t -> (int * float) Seq.t
Iterate on the floatarray, in increasing order, yielding indices along elements. Modifications of the
floatarray during iteration will be reflected in the sequence.
val of_seq : float Seq.t -> t
Create an array from the generator.
val map_to_array : (float -> 'a) -> t -> 'a array
map_to_array f a applies function f to all the elements of a , and builds an array with the results
returned by f : [| f a.(0); f a.(1); ...; f a.(length a - 1) |] .
val map_from_array : ('a -> float) -> 'a array -> t
map_from_array f a applies function f to all the elements of a , and builds a floatarray with the results
returned by f .
Arrays and concurrency safety
Care must be taken when concurrently accessing float arrays from multiple domains: accessing an array
will never crash a program, but unsynchronized accesses might yield surprising
(non-sequentially-consistent) results.
Atomicity
Every float array operation that accesses more than one array element is not atomic. This includes
iteration, scanning, sorting, splitting and combining arrays.
For example, consider the following program:
let size = 100_000_000
let a = Float.Array.make size 1.
let update a f () =
Float.Array.iteri (fun i x -> Float.Array.set a i (f x)) a
let d1 = Domain.spawn (update a (fun x -> x +. 1.))
let d2 = Domain.spawn (update a (fun x -> 2. *. x +. 1.))
let () = Domain.join d1; Domain.join d2
After executing this code, each field of the float array a is either 2. , 3. , 4. or 5. . If
atomicity is required, then the user must implement their own synchronization (for example, using Mutex.t
).
Data races
If two domains only access disjoint parts of the array, then the observed behaviour is the equivalent to
some sequential interleaving of the operations from the two domains.
A data race is said to occur when two domains access the same array element without synchronization and
at least one of the accesses is a write. In the absence of data races, the observed behaviour is
equivalent to some sequential interleaving of the operations from different domains.
Whenever possible, data races should be avoided by using synchronization to mediate the accesses to the
array elements.
Indeed, in the presence of data races, programs will not crash but the observed behaviour may not be
equivalent to any sequential interleaving of operations from different domains. Nevertheless, even in the
presence of data races, a read operation will return the value of some prior write to that location with
a few exceptions.
Tearing
Float arrays have two supplementary caveats in the presence of data races.
First, the blit operation might copy an array byte-by-byte. Data races between such a blit operation and
another operation might produce surprising values due to tearing: partial writes interleaved with other
operations can create float values that would not exist with a sequential execution.
For instance, at the end of
let zeros = Float.Array.make size 0.
let max_floats = Float.Array.make size Float.max_float
let res = Float.Array.copy zeros
let d1 = Domain.spawn (fun () -> Float.Array.blit zeros 0 res 0 size)
let d2 = Domain.spawn (fun () -> Float.Array.blit max_floats 0 res 0 size)
let () = Domain.join d1; Domain.join d2
the res float array might contain values that are neither 0. nor max_float .
Second, on 32-bit architectures, getting or setting a field involves two separate memory accesses. In the
presence of data races, the user may observe tearing on any operation.