PROGRAM 4


--  Filename:  prog3.adb     Author:  Anthony F. Ortiz

WITH Text_IO;    USE Text_IO;
WITH Direct_IO; 

PROCEDURE Ch7P1 is

    --  Input : A test file of key values
    --  Output: A direct nontext file of hashed key values
    --          and synonyms.
    --          The output file is first skeletonized.
    SUBTYPE Key_Type Is String (1..3);
    TYPE Relative_Record_Type Is Record
        key : Key_Type;
        synonym:  integer;
    End Record;

    PACKAGE Key_IO Is New Direct_IO (Relative_Record_Type);
    PACKAGE Positive_IO Is New Text_IO.Integer_IO (Key_IO.Positive_Count);
    PACKAGE Int_IO is new Integer_IO (Integer); use Int_IO;
    Use Key_IO;

    MAX               : Constant Key_IO.Positive_Count := 7;

    address           : Key_IO.Positive_Count;
    home              : Key_IO.Positive_Count;
    input_file        : Text_IO.File_Type;
    input_file_record : Relative_Record_Type;
    last              : Natural;
    record_position   : Key_IO.Positive_Count;
    relative_file     : Key_IO.File_Type;
    relative_record   : Relative_Record_Type;
    hold_record       : Relative_Record_Type;
    change_record     : Relative_Record_Type;
    
FUNCTION Hash (key : Key_Type) Return Key_IO.Positive_Count Is
BEGIN
    Return Key_IO.Positive_Count (Character'Pos (key (2))
                                  - Character'Pos ('0'));
END Hash;

BEGIN  -- Ch7P1
    --  Skeletonize relative file.
    Key_IO.Create (relative_file, Key_IO.OUT_FILE, "A:RELTEST.DAT");
    relative_record.key := "~~~";
    relative_record.synonym := -1;
    For record_position In 1..MAX Loop
        Key_IO.Write (relative_file, relative_record, record_position);
    End Loop;
    Key_IO.Close (relative_file);
    --  Insert records.
    Key_IO.Open (relative_file, Key_IO.INOUT_FILE, "A:RELTEST.DAT");
    Text_IO.Open (input_file, Text_IO.IN_FILE, "A:HASHIN.TXT");
    Text_IO.Put_Line ("KEY => ADDRESS");
    Text_IO.New_Line;
    Loop
        Exit When Text_IO.End_of_File (input_file);
        Text_IO.Get_Line (input_file, input_file_record.key, last);
        Text_IO.Skip_Line (input_file);
        address := Hash (input_file_record.key);
        home := address;
        Text_IO.Put (input_file_record.key);
        Text_IO.Put (" => ");
        Positive_IO.Put (address, 2);
        Text_IO.New_Line;
        Loop
            Key_IO.Read (relative_file, relative_record, address);                
            If home = address then
                hold_record.synonym := relative_record.synonym;
                hold_record.key := relative_record.key;
            End If;
            If relative_record.key = "~~~" Then
                input_file_record.synonym := hold_record.synonym;
                Key_IO.Write (relative_file, input_file_record, address);
                Exit;
            Else
                --  Use linear probing.
                address := address + 1;
                If address > MAX Then
                    address := 1;
                End If;
                --  Write the old file back with the synonym changed.                           
                change_record.synonym := integer (address);
                change_record.key := hold_record.key;
                Key_IO.Write (relative_file, change_record, home);
            End If;
            Exit When address = home;
        End Loop;
    End Loop;
    Text_IO.Close (input_file);
    Text_IO.New_Line;
    --  List file back.
    Key_IO.Reset (relative_file, Key_IO.IN_FILE);
    record_position := 1;
    Text_IO.Put_Line (" # KEY          SYNONYM");
    Text_IO.New_Line;
    Loop
        Exit When Key_IO.End_of_File (relative_file);
        Key_IO.Read (relative_file, relative_record);
        Positive_IO.Put (record_position, 2);
        Text_IO.Put ("   ");
        Text_IO.Put (relative_record.key);
        Put (relative_record.synonym, 10);
        Text_IO.New_Line;
        record_position := record_position + 1;
    End Loop;
    Key_IO.Close (relative_file);
END Ch7P1;

--  data file:  hashin.txt

R5A
R3A
R2A
R3B
R7A
R4A
R3C.

--  data file:  reltest.dat

--  this is not a text file.

--  outfile:  prog3.out

KEY => ADDRESS

R5A =>  5
R3A =>  3
R2A =>  2
R3B =>  3
R7A =>  7
R4A =>  4
R3C =>  3

 # KEY          SYNONYM

 1   R3C         4
 2   R2A        -1
 3   R3A         1
 4   R3B         6
 5   R5A        -1
 6   R4A        -1
 7   R7A        -1




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