Description
Write a complete module that will be used as part of your SIC/XE assembler to evaluate the operand field of an assembly language statement.
- This must be a separate module from the symbol table module developed in assignment #1.
Basic Algorithm
- read symbols and their attributes one line at a time from a text file named DAT.
- SYMBOL VALUE RFLAG
- exact same process was used with step #1 of assignment #1.
- read expressions one at a time from the text file whose name was read from the command line.
- if no file name was specified then prompt the user for the file name.
- evaluate the current expression.
- maximum of two values/operands per expression
- any combination of symbols and numeric literals
- (+) addition and (-) subtraction are the only supported arithmetic operations
- use the table given to determine the expressions overall relocatable flag value
- if the expression begins with = then the operand field contains a literal
- each unique valid literal is inserted into the literal table
- maximum of two values/operands per expression
- display the expression information
- the required output format is shown – order of attributes is required – see last page
- display a detailed error message if the expression is invalid
- display the contents of the literal table
- the required output format is shown – order of attributes is required – see last page
The expression file will contain one expression per line similar to the following (0 or more leading spaces):
GREEN Simple/Direct Addressing – use RFLAG value
@GREEN Indirect Addressing – use RFLAG value
#GREEN Immediate Addressing – use RFLAG value
GREEN,X Indexed Addressing – use RFLAG value
#9 Immediate Addressing – Absolute value
GREEN+YELLOW VALUE + VALUE and RFLAG + RFLAG
GREEN–15 VALUE – 15 and RFLAG – Absolute value
=0cABC Character Literal – 1 character per byte
=0x5A Hexadecimal Literal – 2 hexadecimal digits per byte
Rules for evaluating the relocatability of an expression:
- Absolute value – not relative to the starting address of the program – RFLAG is FALSE (0)
- Relative value – relative to the starting address of the program – RFLAG is TRUE (1)
| RFLAG #1 | Operation | RFLAG #2 | Adjusted RFLAG |
| ABSOLUTE | – | ABSOLUTE | ABSOLUTE |
| ABSOLUTE | – | RELATIVE | ERROR |
| ABSOLUTE | + | ABSOLUTE | ABSOLUTE |
| ABSOLUTE | + | RELATIVE | RELATIVE |
| RELATIVE | – | ABSOLUTE | RELATIVE |
| RELATIVE | – | RELATIVE | ABSOLUTE |
| RELATIVE | + | ABSOLUTE | RELATIVE |
| RELATIVE | + | RELATIVE | ERROR |
Literal Table
- a linked list is used to store each literal along with its associated attributes:
- literal name – the actual literal expression including = and quotes
- g., =0CABC =0Cabc =0X0F =0X123
- g., =0cABC =0cabc =0x0f =0x123
- operand value – object code equivalent in hexadecimal
- g., 414243 616263 0F ERROR
- length in bytes
- g., 3 3 1 ERROR
- address – initially the literal occurrence within the expression file – eventually the actual address
- g., 0 – first literal encountered, 1 – second literal encountered, …
- the literal table would be a good candidate for an additional standalone module.
- literal name – the actual literal expression including = and quotes
Make sure that each module only contains items/operations directly related to that module.
- this applies to all required modules: Symbol Table and Expression Processing
- this applies to all optional modules: Literal Table, String Processing, Error Handling, etc…
- g., the Symbol Table does NOT handle:
- file processing, expression processing, the literal table, string/character processing, most error handling, etc…
- g., the Symbol Table does NOT handle:
Fully document all parts of your program:
- driver/main program
- modules
- header (.h) files
- implementation (.c/.cpp) files
- C# programs adjust accordingly
- see documentation requirements on the course web site
All output should be in an easy to understand format.
- see the example on the last page of this document.
- do not allow results to scroll off the screen.
- temporarily pause the screen where appropriate.
- Tera Term Pro uses a default screen size of approximately 20 lines and 80 columns per line.
- Visual Studio projects adjust accordingly.
All error messages must provide as much detail as possible.
- print out error messages as they are encountered within the expression file
- describe each error in detail as well as display the component or components that generated the error
- make sure not to stop when an error is encountered – process every line in the data file
Expression Processing Example
SYMS.DAT Expression File
RED: 13 TRUE RED
PURPLE: 6 FALSE PURPLE+#17
BLACK: -7 TRUE @BLACK
PINK: 9 TRUE #WHITE
WHITE: 5 FALSE =0CDEFG
WHITE,X
22
=0X5A
PINK+#3
=0X5A
PINK–#3
@#25+RED
=0C5A
#7
When a symbol is encountered its attribute values are determined by looking up the symbol in the symbol table.
EXPRESSIONS
EXPRESSION VALUE RELOCATABLE N-Bit I-Bit X-Bit
RED 13 RELATIVE 1 1 0
PURPLE+#17 23 ABSOLUTE 1 1 0
@BLACK -7 RELATIVE 1 0 0
#WHITE 5 ABSOLUTE 0 1 0
WHITE,X 5 ABSOLUTE 1 1 1
#22 22 ABSOLUTE 0 1 0
PINK+#3 12 RELATIVE 1 1 0
PINK–#3 6 RELATIVE 1 1 0
@#25+RED 38 RELATIVE 1 0 0
#7 7 ABSOLUTE 0 1 0
LITERAL TABLE
NAME VALUE LENGTH ADDRESS
=0CDEFG 44454647 4 1
=0X5A 5A 1 2
=0C5A 3541 2 3
Notes:
- @ # ,X apply to the entire expression not an individual operand within the expression
- g., @(OP1+OP2) #(OP1-OP2) (OP1+OP2),X
- ( ) not part of statement syntax
- Except would be # associated with a numeric literal: PURPLE+#17
- encountering duplicate literals is not an error
- only enter valid literal names the first time each unique one is encountered
- think of them as constants – declared once and used multiple times
- display the contents of the symbol table for debugging purposes
