synthesizable rtl style

Refactored Synthesizable RTL

The module has been refactored according to ASIC-oriented SystemVerilog coding conventions while preserving its original 8-bit addition behavior.

1. Refactored Code

`default_nettype none

module add (
    input  logic [7:0] i_a,
    input  logic [7:0] i_b,
    output logic [7:0] o_sum
);

logic unused_co;

assign {unused_co, o_sum} =
       {1'b0, i_a} + {1'b0, i_b};

endmodule

`default_nettype wire

2. Key Improvements

3. Why These Changes Matter

Explicit hardware intent

Using logic and consistent port prefixes makes signal directions and ownership easier to understand during RTL review.

Predictable arithmetic behavior

Both operands are explicitly zero-extended to 9 bits before addition.

The complete result is assigned to a 9-bit concatenation. The carry-out is captured separately as unused_co, making the intentional truncation visible in the source code.

Improved tool robustness

The default_nettype none directive prevents accidental implicit net declarations caused by misspelled signal names. The previous setting is restored at the end of the file for integration with other compilation units.

Maintainable conventions

Consistent naming and explicit intermediate widths improve readability during synthesis review, waveform debugging, and later design modifications.

4. Functional Behavior

The original module implements 8-bit modular addition:

[
o_sum = (i_a + i_b) \bmod 256
]

For example

The refactoring preserves this behavior. It does not introduce saturation, overflow protection, additional latency, or registers.

5. Important Notes

• The adder remains purely combinational.
• The carry is intentionally unused by downstream logic.
• No new hardware behavior is introduced.
• This is a source-level refactoring; functional equivalence and synthesis results have not been independently verified.

Result: Cleaner RTL with explicit widths, consistent naming, and clearly documented arithmetic intent, suitable for ASIC-oriented development workflows.