Maps in VHDL

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

entity Maps is
end Maps;

architecture Behavioral of Maps is
    -- Define a record type to represent key-value pairs
    type KeyValuePair is record
        key : string(1 to 10);
        value : integer;
    end record;

    -- Define an array type to hold multiple key-value pairs
    type MapType is array (0 to 9) of KeyValuePair;

    -- Function to create an empty map
    function make_map return MapType is
        variable m : MapType;
    begin
        for i in m'range loop
            m(i) := (key => (others => ' '), value => 0);
        end loop;
        return m;
    end function;

    -- Function to set a key-value pair in the map
    procedure set_value(m : inout MapType; k : string; v : integer) is
    begin
        for i in m'range loop
            if m(i).key = k then
                m(i).value := v;
                return;
            elsif m(i).key = (m(i).key'range => ' ') then
                m(i).key := k;
                m(i).value := v;
                return;
            end if;
        end loop;
    end procedure;

    -- Function to get a value from the map
    function get_value(m : MapType; k : string) return integer is
    begin
        for i in m'range loop
            if m(i).key = k then
                return m(i).value;
            end if;
        end loop;
        return 0; -- Return 0 if key not found
    end function;

    -- Function to delete a key-value pair from the map
    procedure delete_key(m : inout MapType; k : string) is
    begin
        for i in m'range loop
            if m(i).key = k then
                m(i) := (key => (others => ' '), value => 0);
                return;
            end if;
        end loop;
    end procedure;

    -- Function to clear all key-value pairs from the map
    procedure clear_map(m : inout MapType) is
    begin
        for i in m'range loop
            m(i) := (key => (others => ' '), value => 0);
        end loop;
    end procedure;

    -- Function to check if a key exists in the map
    function key_exists(m : MapType; k : string) return boolean is
    begin
        for i in m'range loop
            if m(i).key = k then
                return true;
            end if;
        end loop;
        return false;
    end function;

begin
    process
        variable m : MapType := make_map;
    begin
        -- Set key/value pairs
        set_value(m, "k1      ", 7);
        set_value(m, "k2      ", 13);

        -- Print the map (this would typically be done with a custom print function)
        report "map: " & integer'image(get_value(m, "k1      ")) & ", " & integer'image(get_value(m, "k2      "));

        -- Get a value for a key
        report "v1: " & integer'image(get_value(m, "k1      "));

        -- Get a value for a non-existent key
        report "v3: " & integer'image(get_value(m, "k3      "));

        -- Get the number of key/value pairs (this would typically be a function)
        report "len: 2";

        -- Delete a key/value pair
        delete_key(m, "k2      ");
        report "map after delete: " & integer'image(get_value(m, "k1      "));

        -- Clear all key/value pairs
        clear_map(m);
        report "map after clear: empty";

        -- Check if a key exists
        report "k2 exists: " & boolean'image(key_exists(m, "k2      "));

        -- Create a new map with initial values
        set_value(m, "foo     ", 1);
        set_value(m, "bar     ", 2);
        report "new map: " & integer'image(get_value(m, "foo     ")) & ", " & integer'image(get_value(m, "bar     "));

        wait;
    end process;
end Behavioral;

This VHDL code demonstrates the concept of maps (associative arrays) using a custom implementation. Here’s an explanation of the key points:

We define a KeyValuePair record type to represent key-value pairs, and a MapType array to hold multiple pairs.
Functions and procedures are implemented to mimic map operations:
- make_map: Creates an empty map
- set_value: Sets a key-value pair
- get_value: Retrieves a value for a given key
- delete_key: Removes a key-value pair
- clear_map: Removes all key-value pairs
- key_exists: Checks if a key exists in the map
The main process demonstrates the usage of these map operations, similar to the original example.
VHDL doesn’t have built-in associative arrays, so this implementation uses a fixed-size array and linear search. In practice, more efficient data structures might be used for larger maps.
String handling in VHDL is different from high-level languages. Fixed-length strings are used here for simplicity.
Printing in VHDL is typically done through simulator-specific mechanisms. The report statements here are used to demonstrate the output.

This VHDL implementation provides similar functionality to the original example, adapted to VHDL’s language features and constraints.

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Maps in VHDL