Regular Expressions in VHDL

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity RegularExpressions is
end RegularExpressions;

architecture Behavioral of RegularExpressions is
    -- Function to simulate string matching
    function match_string(pattern : string; input : string) return boolean is
    begin
        -- This is a simplified simulation of regex matching
        -- In real VHDL, you would need to implement a full regex engine
        return pattern = input;
    end function;

    -- Function to simulate finding a string
    function find_string(pattern : string; input : string) return string is
    begin
        -- This is a simplified simulation of regex find
        -- In real VHDL, you would need to implement a full regex engine
        if input'length >= pattern'length then
            return input(input'left to input'left + pattern'length - 1);
        else
            return "";
        end if;
    end function;

begin
    process
        variable match_result : boolean;
        variable find_result : string(1 to 5);
    begin
        -- This tests whether a pattern matches a string.
        match_result := match_string("peach", "peach");
        report "Match result: " & boolean'image(match_result);

        -- This finds the match for the pattern.
        find_result := find_string("peach", "peach punch");
        report "Find result: " & find_result;

        -- Note: VHDL doesn't have built-in support for regular expressions.
        -- For complex pattern matching, you would need to implement a custom regex engine
        -- or use external libraries if available in your VHDL environment.

        wait;
    end process;
end Behavioral;

This VHDL code provides a basic simulation of regular expression functionality. However, it’s important to note that VHDL doesn’t have built-in support for regular expressions like many software programming languages do.

The code defines two functions:

match_string: Simulates matching a pattern against an input string.
find_string: Simulates finding a pattern in an input string.

These functions are very simplified and don’t provide the full power of regular expressions. In a real VHDL project, you would need to implement a more sophisticated regex engine if you need complex pattern matching capabilities.

The process in the architecture body demonstrates how to use these functions:

It tests whether the pattern “peach” matches the string “peach”.
It tries to find the pattern “peach” in the string “peach punch”.

To run this VHDL code, you would need to use a VHDL simulator. The exact commands would depend on your specific VHDL development environment.

Remember, VHDL is primarily used for hardware description and synthesis, not for text processing. If you need advanced text processing capabilities in your hardware design, you might need to consider using a soft-core processor or custom logic specifically designed for text processing.

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Regular Expressions in VHDL