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Library
Module
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Class type
Large, multi-dimensional, numerical arrays.
This module implements multi-dimensional arrays of integers and floating-point numbers, thereafter referred to as 'Bigarrays', to distinguish them from the standard OCaml arrays described in Array.
The implementation allows efficient sharing of large numerical arrays between OCaml code and C or Fortran numerical libraries.
The main differences between 'Bigarrays' and standard OCaml arrays are as follows:
- Bigarrays are not limited in size, unlike OCaml arrays. (Normal float arrays are limited to 2,097,151 elements on a 32-bit platform, and normal arrays of other types to 4,194,303 elements.)
- Bigarrays are multi-dimensional. Any number of dimensions between 0 and 16 is supported. In contrast, OCaml arrays are mono-dimensional and require encoding multi-dimensional arrays as arrays of arrays.
- Bigarrays can only contain integers and floating-point numbers, while OCaml arrays can contain arbitrary OCaml data types.
- Bigarrays provide more space-efficient storage of integer and floating-point elements than normal OCaml arrays, in particular because they support 'small' types such as single-precision floats and 8 and 16-bit integers, in addition to the standard OCaml types of double-precision floats and 32 and 64-bit integers.
- The memory layout of Bigarrays is entirely compatible with that of arrays in C and Fortran, allowing large arrays to be passed back and forth between OCaml code and C / Fortran code with no data copying at all.
- Bigarrays support interesting high-level operations that normal arrays do not provide efficiently, such as extracting sub-arrays and 'slicing' a multi-dimensional array along certain dimensions, all without any copying.
Users of this module are encouraged to do open Bigarray in their source, then refer to array types and operations via short dot notation, e.g. Array1.t or Array2.sub.
Bigarrays support all the OCaml ad-hoc polymorphic operations:
- comparisons (
=,<>,<=, etc, as well asStdlib.compare); - hashing (module
Hash); - and structured input-output (the functions from the
Marshalmodule, as well asStdlib.output_valueandStdlib.input_value).
Element kinds
Bigarrays can contain elements of the following kinds:
- IEEE single precision (32 bits) floating-point numbers (
Bigarray.float32_elt), - IEEE double precision (64 bits) floating-point numbers (
Bigarray.float64_elt), - IEEE single precision (2 * 32 bits) floating-point complex numbers (
Bigarray.complex32_elt), - IEEE double precision (2 * 64 bits) floating-point complex numbers (
Bigarray.complex64_elt), - 8-bit integers (signed or unsigned) (
Bigarray.int8_signed_eltorBigarray.int8_unsigned_elt), - 16-bit integers (signed or unsigned) (
Bigarray.int16_signed_eltorBigarray.int16_unsigned_elt), - OCaml integers (signed, 31 bits on 32-bit architectures, 63 bits on 64-bit architectures) (
Bigarray.int_elt), - 32-bit signed integers (
Bigarray.int32_elt), - 64-bit signed integers (
Bigarray.int64_elt), - platform-native signed integers (32 bits on 32-bit architectures, 64 bits on 64-bit architectures) (
Bigarray.nativeint_elt).
Each element kind is represented at the type level by one of the *_elt types defined below (defined with a single constructor instead of abstract types for technical injectivity reasons).
- since 4.07.0 Moved from otherlibs to stdlib.
type ('a, 'b) kind = | Float32 : (float, float32_elt) kind| Float64 : (float, float64_elt) kind| Int8_signed : (int, int8_signed_elt) kind| Int8_unsigned : (int, int8_unsigned_elt) kind| Int16_signed : (int, int16_signed_elt) kind| Int16_unsigned : (int, int16_unsigned_elt) kind| Int32 : (int32, int32_elt) kind| Int64 : (int64, int64_elt) kind| Int : (int, int_elt) kind| Nativeint : (nativeint, nativeint_elt) kind| Complex32 : (Complex.t, complex32_elt) kind| Complex64 : (Complex.t, complex64_elt) kind| Char : (char, int8_unsigned_elt) kind
To each element kind is associated an OCaml type, which is the type of OCaml values that can be stored in the Bigarray or read back from it. This type is not necessarily the same as the type of the array elements proper: for instance, a Bigarray whose elements are of kind float32_elt contains 32-bit single precision floats, but reading or writing one of its elements from OCaml uses the OCaml type float, which is 64-bit double precision floats.
The GADT type ('a, 'b) kind captures this association of an OCaml type 'a for values read or written in the Bigarray, and of an element kind 'b which represents the actual contents of the Bigarray. Its constructors list all possible associations of OCaml types with element kinds, and are re-exported below for backward-compatibility reasons.
Using a generalized algebraic datatype (GADT) here allows writing well-typed polymorphic functions whose return type depend on the argument type, such as:
let zero : type a b. (a, b) kind -> a = function
| Float32 -> 0.0 | Complex32 -> Complex.zero
| Float64 -> 0.0 | Complex64 -> Complex.zero
| Int8_signed -> 0 | Int8_unsigned -> 0
| Int16_signed -> 0 | Int16_unsigned -> 0
| Int32 -> 0l | Int64 -> 0L
| Int -> 0 | Nativeint -> 0n
| Char -> '\000'val float32 : (float, float32_elt) kindSee Bigarray.char.