Type Conversion
Formal Definition
An expression that converts the
value of a subexpression from one type to the designated type of the
type conversion.
Simplified Syntax
type_mark ( expression )
Description
VHDL is a strongly typed language. This causes that objects of even
closely related types need a conversion, if they are supposed to be
used together.
The result of the conversion is an object, which type is the same as
the type specified by the type_mark (Example 1). The type of the
operand (the expression) must be known independently from the
context. Moreover, the operand cannot be an aggregate, an allocator,
the literal null, or a
string literal.
A type conversion is restricted to closely related types, i.e. must
conform to the following rules::
-
All abstract numeric types (integers and floating point numbers) are
closely related types. When a floating-point number is converted into
an integer, the result is rounded to the nearest integer.
-
Two arrays are closely related types if:
-
Both arrays have the same dimensions,
-
their elements are of the same type,
-
for each range, the index types are the same or closely related.
-
No other types are closely related.
If the type_mark indicates an unrestricted array type, then after the
conversion the range boundaries are moved from the operand. If the
type_mark indicates a restricted array type, then the range
boundaries of the array are described based on this type. After the
conversion, the elements values of the array are equal to the
elements values before the conversion.
Examples
Example 1
variable Data_Calc,
Param_Calc : integer;
. . .
Data_Calc := Integer(74.94 * real(Param_Calc));
This assignment contains two type conversions: first Param_Calc is
converted to a real value in order to multiply it with a universal
real. Then the result of the multiplication is converted back to an
integer and assigned to Data_Calc.
Important Notes
|
