Lecture 5

Pseudo instructions, macros, and includes. Conditions, loops, loads, and stores.

Lecture

Slides (PDF, PPTX).

Outline

• Program structure: segments and labels.
• Branch instructions and their use in conditions and loops.
• Data segment and data directives (.byte, .half, .word, .space, .align, .ascii, .asciz).
• Load and store instructions and their use for accessing static data.
• Macros (directives .macro, .end_macro, .include, and .eqv)
• Examples of programs processing static variables stored in the data segment.

Examples:

• hello.s
• if_then_else.s
• while.s
• for.s
• for_nested.s
• macros1.s
• macros2.s
• macros3.s
• macrolib.s
• fibonacci.s
• euclid.s
• data.s
• loadstore.s
• loadstore2.s
• loadstore3.s
• min_max.s

Workshop

Outline

• Study and run all the examples from the lecture.
• Practice writing programs with conditions and loops.
• Practice writing programs that access values in the data segment.
• Practice using macros. Pay attention to the code generated from macros.

Tasks

1. Write a program that inputs two integer values x and y and prints all the values in the range min(x, y)..max(x, y).

2. Write a program that fills an array of 32 integers from values from the standard input. It reads values in a loop and finishes reading when all 32 values are read or when value 0 is read.

3. Write a program that inputs two positive integer values N and D, finds their quatient (Q) and remainder (R) using the algorithm below, prints the result.

   function divide_unsigned(N, D)
       Q := 0; R := N
       while R ≥ D do
          Q := Q + 1
          R := R − D
       end
      return (Q, R)
   end
   

4. Write your own macros print_hex and print_bin for printing values in hexadecimal and binary formats respectively. What if you want to print immediate values? What kind of macro do you need in this case?

5. Write a program that inputs two unsigned integer values x and y, calculates x ** y (x raised to the power of y), and prints the result. The exponentiation should be implemented as a multiplication in a loop. If an overflow occurs, the program must exit the loop and print an error message.

Homework

Solve the following tasks:

1. DoubleSum
2. DigitSum
3. PlusMinus
4. EvenBack
5. NoDups

Commit the programs to your private GitHub account. Place them into the folder ca/lab05.

References

• RARS help system (click in the main menu Help > Help or press F1).
• Multiplication and division algorithms. Sections 3.3 and 3.4 in [CODR] and Appendix J in [CAQA].
• Macros (Wikipedia).
• Macros in Assembly Language (Wikipedia).
• RISC-V Assembly Programmer’s Manual.
• Memory Alignment (Wikipedia).