Type Casting

What is Type Casting? #

Type casting is the process of converting one data type into another. It is especially useful when working with different bit-widths, enum, struct, or class types.

SystemVerilog supports two types of casting:

1. Static Casting (done at compile-time)
2. Dynamic Casting (done at runtime, especially with classes).

Why Type Casting is Important #

• Prevents mismatched assignments
• Ensures correct data size and interpretation
• Enables class polymorphism
• Helps in hardware modeling (e.g., casting bit-vectors, enums)

1. Static Casting #

Static casting is used to convert values at compile-time between compatible types like enums, bit-vectors, and integers.

Syntax:

<data_type'(expression)

Example:

module static_cast;
  int a = 65;          // 32-bit integer
  byte b;              // 8-bit integer

  initial begin
    b = byte'(a);      // Static cast from int to byte
    $display("Value of b = %0d", b);  
  end
endmodule

Output:

Value of b = 65

Explanation: #

• a is an int (32-bit)
• b is a byte (8-bit)
• We convert a to byte using byte'(a)
• Since 65 fits in 8 bits, b gets the value 65

2. Dynamic Casting using $cast #

Dynamic casting is used at runtime, mostly with class handles. It checks if the object types are compatible before casting.

Syntax:

$cast(Destination, Source)

Example: