Module Bigarray
: sigend
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 openBigarray 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 as compare );
-hashing (module Hash );
-and structured input-output (the functions from the Marshal module, as well as output_value and
input_value ).
Elementkinds
Bigarrays can contain elements of the following kinds:
-IEEE half precision (16 bits) floating-point numbers ( Bigarray.float16_elt ),
-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_elt or Bigarray.int8_unsigned_elt ),
-16-bit integers (signed or unsigned) ( Bigarray.int16_signed_elt or Bigarray.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).
typefloat16_elt =
| Float16_elt
typefloat32_elt =
| Float32_elt
typefloat64_elt =
| Float64_elt
typeint8_signed_elt =
| Int8_signed_elt
typeint8_unsigned_elt =
| Int8_unsigned_elt
typeint16_signed_elt =
| Int16_signed_elt
typeint16_unsigned_elt =
| Int16_unsigned_elt
typeint32_elt =
| Int32_elt
typeint64_elt =
| Int64_elt
typeint_elt =
| Int_elt
typenativeint_elt =
| Nativeint_elt
typecomplex32_elt =
| Complex32_elt
typecomplex64_elt =
| Complex64_elt
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
| Float16 :(float,float16_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:
letzero:typeab.(a,b)kind->a=function|Float32->0.0|Complex32->Complex.zero|Float64->0.0|Complex64->Complex.zero|Float16->0.0|Int8_signed->0|Int8_unsigned->0|Int16_signed->0|Int16_unsigned->0|Int32->0l|Int64->0L|Int->0|Nativeint->0n|Char->'\000'Since 5.2 Constructor Float16 for the GADT.
valfloat16 : (float,float16_elt)kind
See Bigarray.char .
Since 5.2
valfloat32 : (float,float32_elt)kind
See Bigarray.char .
valfloat64 : (float,float64_elt)kind
See Bigarray.char .
valcomplex32 : (Complex.t,complex32_elt)kind
See Bigarray.char .
valcomplex64 : (Complex.t,complex64_elt)kind
See Bigarray.char .
valint8_signed : (int,int8_signed_elt)kind
See Bigarray.char .
valint8_unsigned : (int,int8_unsigned_elt)kind
See Bigarray.char .
valint16_signed : (int,int16_signed_elt)kind
See Bigarray.char .
valint16_unsigned : (int,int16_unsigned_elt)kind
See Bigarray.char .
valint : (int,int_elt)kind
See Bigarray.char and Bigarray.elementkinds .
Beware that this is a bigarray containing OCaml integers (signed, 31 bits on 32-bit architectures, 63
bits on 64-bit architectures), which does not match the C int type.
valint32 : (int32,int32_elt)kind
See Bigarray.char .
valint64 : (int64,int64_elt)kind
See Bigarray.char .
valnativeint : (nativeint,nativeint_elt)kind
See Bigarray.char .
valchar : (char,int8_unsigned_elt)kind
As shown by the types of the values above, Bigarrays of kind float16_elt , float32_elt and float64_elt
are accessed using the OCaml type float . Bigarrays of complex kinds complex32_elt , complex64_elt are
accessed with the OCaml type Complex.t . Bigarrays of integer kinds are accessed using the smallest OCaml
integer type large enough to represent the array elements: int for 8- and 16-bit integer Bigarrays, as
well as OCaml-integer Bigarrays; int32 for 32-bit integer Bigarrays; int64 for 64-bit integer Bigarrays;
and nativeint for platform-native integer Bigarrays. Finally, Bigarrays of kind int8_unsigned_elt can
also be accessed as arrays of characters instead of arrays of small integers, by using the kind value
char instead of int8_unsigned .
valkind_size_in_bytes : ('a,'b)kind->intkind_size_in_bytesk is the number of bytes used to store an element of type k .
Since 4.03
Arraylayoutstypec_layout =
| C_layout_typ
See Bigarray.fortran_layout .
typefortran_layout =
| Fortran_layout_typ
To facilitate interoperability with existing C and Fortran code, this library supports two different
memory layouts for Bigarrays, one compatible with the C conventions, the other compatible with the
Fortran conventions.
In the C-style layout, array indices start at 0, and multi-dimensional arrays are laid out in row-major
format. That is, for a two-dimensional array, all elements of row 0 are contiguous in memory, followed
by all elements of row 1, etc. In other terms, the array elements at (x,y) and (x,y+1) are adjacent in
memory.
In the Fortran-style layout, array indices start at 1, and multi-dimensional arrays are laid out in
column-major format. That is, for a two-dimensional array, all elements of column 0 are contiguous in
memory, followed by all elements of column 1, etc. In other terms, the array elements at (x,y) and (x+1,y) are adjacent in memory.
Each layout style is identified at the type level by the phantom types Bigarray.c_layout and
Bigarray.fortran_layout respectively.
Supportedlayouts
The GADT type 'alayout represents one of the two supported memory layouts: C-style or Fortran-style. Its
constructors are re-exported as values below for backward-compatibility reasons.
type'alayout =
| C_layout :c_layoutlayout
| Fortran_layout :fortran_layoutlayoutvalc_layout : c_layoutlayoutvalfortran_layout : fortran_layoutlayoutGenericarrays(ofarbitrarilymanydimensions)moduleGenarray:sigendZero-dimensionalarraysmoduleArray0:sigend
Zero-dimensional arrays. The Array0 structure provides operations similar to those of Bigarray.Genarray ,
but specialized to the case of zero-dimensional arrays that only contain a single scalar value.
Statically knowing the number of dimensions of the array allows faster operations, and more precise
static type-checking.
Since 4.05
One-dimensionalarraysmoduleArray1:sigend
One-dimensional arrays. The Array1 structure provides operations similar to those of Bigarray.Genarray ,
but specialized to the case of one-dimensional arrays. (The Bigarray.Array2 and Bigarray.Array3
structures below provide operations specialized for two- and three-dimensional arrays.) Statically
knowing the number of dimensions of the array allows faster operations, and more precise static
type-checking.
Two-dimensionalarraysmoduleArray2:sigend
Two-dimensional arrays. The Array2 structure provides operations similar to those of Bigarray.Genarray ,
but specialized to the case of two-dimensional arrays.
Three-dimensionalarraysmoduleArray3:sigend
Three-dimensional arrays. The Array3 structure provides operations similar to those of Bigarray.Genarray
, but specialized to the case of three-dimensional arrays.
CoercionsbetweengenericBigarraysandfixed-dimensionBigarraysvalgenarray_of_array0 : ('a,'b,'c)Array0.t->('a,'b,'c)Genarray.t
Return the generic Bigarray corresponding to the given zero-dimensional Bigarray.
Since 4.05
valgenarray_of_array1 : ('a,'b,'c)Array1.t->('a,'b,'c)Genarray.t
Return the generic Bigarray corresponding to the given one-dimensional Bigarray.
valgenarray_of_array2 : ('a,'b,'c)Array2.t->('a,'b,'c)Genarray.t
Return the generic Bigarray corresponding to the given two-dimensional Bigarray.
valgenarray_of_array3 : ('a,'b,'c)Array3.t->('a,'b,'c)Genarray.t
Return the generic Bigarray corresponding to the given three-dimensional Bigarray.
valarray0_of_genarray : ('a,'b,'c)Genarray.t->('a,'b,'c)Array0.t
Return the zero-dimensional Bigarray corresponding to the given generic Bigarray.
Since 4.05
RaisesInvalid_argument if the generic Bigarray does not have exactly zero dimension.
valarray1_of_genarray : ('a,'b,'c)Genarray.t->('a,'b,'c)Array1.t
Return the one-dimensional Bigarray corresponding to the given generic Bigarray.
RaisesInvalid_argument if the generic Bigarray does not have exactly one dimension.
valarray2_of_genarray : ('a,'b,'c)Genarray.t->('a,'b,'c)Array2.t
Return the two-dimensional Bigarray corresponding to the given generic Bigarray.
RaisesInvalid_argument if the generic Bigarray does not have exactly two dimensions.
valarray3_of_genarray : ('a,'b,'c)Genarray.t->('a,'b,'c)Array3.t
Return the three-dimensional Bigarray corresponding to the given generic Bigarray.
RaisesInvalid_argument if the generic Bigarray does not have exactly three dimensions.
Re-shapingBigarraysvalreshape : ('a,'b,'c)Genarray.t->intarray->('a,'b,'c)Genarray.treshapeb[|d1;...;dN|] converts the Bigarray b to a N -dimensional array of dimensions d1 ... dN . The
returned array and the original array b share their data and have the same layout. For instance,
assuming that b is a one-dimensional array of dimension 12, reshapeb[|3;4|] returns a two-dimensional
array b' of dimensions 3 and 4. If b has C layout, the element (x,y) of b' corresponds to the element x*3+y of b . If b has Fortran layout, the element (x,y) of b' corresponds to the element x+(y-1)*4 of b . The returned Bigarray must have exactly the same number of elements as the original Bigarray b
. That is, the product of the dimensions of b must be equal to i1*...*iN . Otherwise,
Invalid_argument is raised.
valreshape_0 : ('a,'b,'c)Genarray.t->('a,'b,'c)Array0.t
Specialized version of Bigarray.reshape for reshaping to zero-dimensional arrays.
Since 4.05
valreshape_1 : ('a,'b,'c)Genarray.t->int->('a,'b,'c)Array1.t
Specialized version of Bigarray.reshape for reshaping to one-dimensional arrays.
valreshape_2 : ('a,'b,'c)Genarray.t->int->int->('a,'b,'c)Array2.t
Specialized version of Bigarray.reshape for reshaping to two-dimensional arrays.
valreshape_3 : ('a,'b,'c)Genarray.t->int->int->int->('a,'b,'c)Array3.t
Specialized version of Bigarray.reshape for reshaping to three-dimensional arrays.
Bigarraysandconcurrencysafety
Care must be taken when concurrently accessing bigarrays from multiple domains: accessing a bigarray will
never crash a program, but unsynchronized accesses might yield surprising (non-sequentially-consistent)
results.
Atomicity
Every bigarray operation that accesses more than one array element is not atomic. This includes slicing,
bliting, and filling bigarrays.
For example, consider the following program:
openBigarrayletsize=100_000_000leta=Array1.initIntC_layoutsize(fun_->1)letupdatefa()=fori=0tosize-1doa.{i}<-fa.{i}doneletd1=Domain.spawn(update(funx->x+1)a)letd2=Domain.spawn(update(funx->2*x+1)a)let()=Domain.joind1;Domain.joind2
After executing this code, each field of the bigarray 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 ).
Dataraces
If two domains only access disjoint parts of the bigarray, 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 bigarray 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
bigarray 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.
Tearing
Bigarrays have a distinct caveat in the presence of data races: concurrent bigarray operations might
produce surprising values due to tearing. More precisely, the interleaving of partial writes and reads
might create values that would not exist with a sequential execution. For instance, at the end of
letres=Array1.initComplex64c_layoutsize(fun_->Complex.zero)letd1=Domain.spawn(fun()->Array1.fillresComplex.one)letd2=Domain.spawn(fun()->Array1.fillresComplex.i)let()=Domain.joind1;Domain.joind2
the res bigarray might contain values that are neither Complex.i nor Complex.one (for instance 1+i ).
OCamldoc 2025-06-12 Bigarray(3o)
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