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-- Copyright (C) 2002 Morgan Kaufmann Publishers, Inc
-- This file is part of VESTs (Vhdl tESTs).
-- VESTs is free software; you can redistribute it and/or modify it
-- under the terms of the GNU General Public License as published by the
-- Free Software Foundation; either version 2 of the License, or (at
-- your option) any later version.
-- VESTs is distributed in the hope that it will be useful, but WITHOUT
-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-- FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
-- for more details.
-- You should have received a copy of the GNU General Public License
-- along with VESTs; if not, write to the Free Software Foundation,
-- Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
package bounded_buffer_adt is
subtype byte is bit_vector(0 to 7);
type bounded_buffer_object; -- private
type bounded_buffer is access bounded_buffer_object;
function new_bounded_buffer ( size : in positive ) return bounded_buffer;
-- creates a bounded buffer object with 'size' bytes of storage
procedure test_empty ( variable the_bounded_buffer : in bounded_buffer;
is_empty : out boolean );
-- tests whether the bounded buffer is empty (i.e., no data to read)
procedure test_full ( variable the_bounded_buffer : in bounded_buffer;
is_full : out boolean );
-- tests whether the bounded buffer is full (i.e., no data can be written)
procedure write ( the_bounded_buffer : inout bounded_buffer; data : in byte );
-- if the bounded buffer is not full, writes the data
-- if it is full, assertion violation with severity failure
procedure read ( the_bounded_buffer : inout bounded_buffer; data : out byte );
-- if the bounded buffer is not empty, read the first byte of data
-- if it is empty, assertion violation with severity failure
----------------------------------------------------------------
-- the following types are private to the ADT
type store_array is array (natural range <>) of byte;
type store_ptr is access store_array;
type bounded_buffer_object is record
byte_count : natural;
head_index, tail_index : natural;
store : store_ptr;
end record bounded_buffer_object;
end package bounded_buffer_adt;
package body bounded_buffer_adt is
function new_bounded_buffer ( size : in positive ) return bounded_buffer is
begin
return new bounded_buffer_object'(
byte_count => 0, head_index => 0, tail_index => 0,
store => new store_array(0 to size - 1) );
end function new_bounded_buffer;
procedure test_empty ( variable the_bounded_buffer : in bounded_buffer;
is_empty : out boolean ) is
begin
is_empty := the_bounded_buffer.byte_count = 0;
end procedure test_empty;
procedure test_full ( variable the_bounded_buffer : in bounded_buffer;
is_full : out boolean ) is
begin
is_full := the_bounded_buffer.byte_count = the_bounded_buffer.store'length;
end procedure test_full;
procedure write ( the_bounded_buffer : inout bounded_buffer; data : in byte ) is
variable buffer_full : boolean;
begin
test_full(the_bounded_buffer, buffer_full);
if buffer_full then
report "write to full bounded buffer" severity failure;
else
the_bounded_buffer.store(the_bounded_buffer.tail_index) := data;
the_bounded_buffer.tail_index := (the_bounded_buffer.tail_index + 1)
mod the_bounded_buffer.store'length;
the_bounded_buffer.byte_count := the_bounded_buffer.byte_count + 1;
end if;
end procedure write;
procedure read ( the_bounded_buffer : inout bounded_buffer; data : out byte ) is
variable buffer_empty : boolean;
begin
test_empty(the_bounded_buffer, buffer_empty);
if buffer_empty then
report "read from empty bounded buffer" severity failure;
else
data := the_bounded_buffer.store(the_bounded_buffer.head_index);
the_bounded_buffer.head_index := (the_bounded_buffer.head_index + 1)
mod the_bounded_buffer.store'length;
the_bounded_buffer.byte_count := the_bounded_buffer.byte_count - 1;
end if;
end procedure read;
end package body bounded_buffer_adt;
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