module Array: sig .. end
Float arrays with packed representation.
type t = floatarray
The type of float arrays with packed representation.
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
.
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
.
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
.
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.
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
.
Invalid_argument
if n < 0
or n > 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
.
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
.
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
.
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.
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
.
Invalid_argument
if the length of l
is greater than
Sys.max_floatarray_length
.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 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 fold_left : ('a -> float -> 'a) -> 'a -> t -> 'a
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 -> 'a -> 'a) -> t -> 'a -> 'a
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
.
val iter2 : (float -> float -> unit) -> t -> t -> unit
Array.iter2 f a b
applies function f
to all the elements of a
and b
.
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)|]
.
Invalid_argument
if the floatarrays are not the same size.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.
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
< 0cmp x y
>= 0 and cmp y z
>= 0 then cmp x z
>= 0When 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 >= jval 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 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
.
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.
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
).
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.
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.