8. Intrinsic Subprograms#
GNAT allows a user application program to write the declaration:
pragma Import (Intrinsic, name);
providing that the name corresponds to one of the implemented intrinsic subprograms in GNAT, and that the parameter profile of the referenced subprogram meets the requirements. This chapter describes the set of implemented intrinsic subprograms, and the requirements on parameter profiles. Note that no body is supplied; as with other uses of pragma Import, the body is supplied elsewhere (in this case by the compiler itself). Note that any use of this feature is potentially non-portable, since the Ada standard does not require Ada compilers to implement this feature.
8.1. Intrinsic Operators#
All the predefined numeric operators in package Standard
in pragma Import (Intrinsic,..)
declarations. In the binary operator case, the operands must have the same
size. The operand or operands must also be appropriate for
the operator. For example, for addition, the operands must
both be floating-point or both be fixed-point, and the
right operand for "**"
must have a root type of
Standard.Integer'Base
.
You can use an intrinsic operator declaration as in the following example:
type Int1 is new Integer;
type Int2 is new Integer;
function "+" (X1 : Int1; X2 : Int2) return Int1;
function "+" (X1 : Int1; X2 : Int2) return Int2;
pragma Import (Intrinsic, "+");
This declaration would permit ‘mixed mode’ arithmetic on items
of the differing types Int1
and Int2
.
It is also possible to specify such operators for private types, if the
full views are appropriate arithmetic types.
8.2. Compilation_ISO_Date#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Compilation_ISO_Date
to obtain the date of
the current compilation (in local time format YYYY-MM-DD).
8.3. Compilation_Date#
Same as Compilation_ISO_Date, except the string is in the form MMM DD YYYY.
8.4. Compilation_Time#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Compilation_Time
to obtain the time of
the current compilation (in local time format HH:MM:SS).
8.5. Enclosing_Entity#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Enclosing_Entity
to obtain the name of
the current subprogram, package, task, entry, or protected subprogram.
8.6. Exception_Information#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Information
to obtain
the exception information associated with the current exception.
8.7. Exception_Message#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Message
to obtain
the message associated with the current exception.
8.8. Exception_Name#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Current_Exception
. The only useful
use of the intrinsic import in this case is the one in this unit,
so an application program should simply call the function
GNAT.Current_Exception.Exception_Name
to obtain
the name of the current exception.
8.9. File#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.File
to obtain the name of the current
file.
8.10. Line#
This intrinsic subprogram is used in the implementation of the
library package GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Line
to obtain the number of the current
source line.
8.11. Shifts and Rotates#
In standard Ada, the shift and rotate functions are available only
for the predefined modular types in package Interfaces
. However, in
GNAT it is possible to define these functions for any integer
type (signed or modular), as in this example:
function Shift_Left
(Value : T;
Amount : Natural) return T
with Import, Convention => Intrinsic;
The function name must be one of
Shift_Left, Shift_Right, Shift_Right_Arithmetic, Rotate_Left, or
Rotate_Right. T must be an integer type. T’Size must be
8, 16, 32 or 64 bits; if T is modular, the modulus
must be 2**8, 2**16, 2**32 or 2**64.
The result type must be the same as the type of Value
.
The shift amount must be Natural.
The formal parameter names can be anything.
A more convenient way of providing these shift operators is to use the Provide_Shift_Operators pragma, which provides the function declarations and corresponding pragma Import’s for all five shift functions. For signed types the semantics of these operators is to interpret the bitwise result of the corresponding operator for modular type. In particular, shifting a negative number may change its sign bit to positive.
8.12. Source_Location#
This intrinsic subprogram is used in the implementation of the
library routine GNAT.Source_Info
. The only useful use of the
intrinsic import in this case is the one in this unit, so an
application program should simply call the function
GNAT.Source_Info.Source_Location
to obtain the current
source file location.