Table of Contents

1 Introduction

In this assignment you need to write x86-64 assembly by hand. This is not something most programmers do often, but when it comes up in the workplace being one of the few there who can do it will help your company and make you shine.

Write your code in a file named matlib.s. We provide a base file that includes the input and output interaction (in main and printNum) to test the code you will write: matlib.s. Write your code where the comments say “TO DO: write this function”.

2 Work with NX

You don’t have to do this, but we strongly recommend you work with NX throughout this assignment.

Log in to NX (see lab01 for a reminder on how to do this).
Open a terminal
Use [the modules tool] to get access to an assembler by typing
```
 module load clang-llvm
```
We suggest using a terminal-based editor. nano is easy to learn because it lists its own keyboard shortcuts at the bottom of the screen (note it uses ^ to mean “while pressing the control key”). emacs is more involved to learn, but also more powerful. vim is a modal editor that is even harder to learn, but those who learn it tend to revere with almost religious passion.

Why a terminal-based editor?

It is common to interact with servers that do not have their own monitors. In these cases, you typically attach to the server via ssh and have access only to a terminal, not a full windowing environment. The more comfortable you are with doing common programming tasks in the terminal, the better these experiences will be.

3 Write two functions

In AT&T syntax x86-64 assembly, write two routines: one that computes the product of two numbers, and one that computes the power of two numbers.

It should be possible to assemble your code by typing clang matlib.s to generate a file, a.out, that can be run by by typing ./a.out. When run, it should¹ ask for two integers and display their product and exponent.

3.1 Product

The first subroutine, product, should compute and return the product of the two integer arguments. It must not use multiplication or division instructions. It must compute this iteratively, not recursively.

There are other correct solutions, but a simple one might follow an approach like the following pseudo-code:

function product(x, y)
    z = 0
    while y > 0 repeat
        z += x
        y -= 1
    end while
    return z
end function

There also exists a much more efficient solution that uses bit shifts.

You may assume that both of the parameters are positive integers (i.e., neither negative or zero) and that the result can fit in a single 64-bit register.

3.2 Power

The second subroutine, power, should compute and return its first argument raised to the power of its second argument. It must use the product routine you wrote to do this, not x86-64 multiplication instructions or other routines you did not write. It must compute this recursively, not iteratively.

There are other correct solutions, but a simple one might follow an approach like the following pseudo-code:

function power(x, y)
    if y == 1 then
        return x
    else
        return product(x, power(x, y-1))
    end if
end function

You may assume that both of the parameters are positive integers (i.e., neither negative or zero) and that the result can fit in a single 64-bit register.

4 Submit

Submit your assembly as matlib.s.

Along the way, you might accidentally write code that runs forever. If the program freezes while running, try pressing Ctrl+C to interrupt it.↩