Description

Assignment 1 – Data Lab: Manipulating Bits
Osman Batur ˙Ince (oince22@ku.edu.tr) is the lead person for this assignment.
1 Introduction
The purpose of this assignment is to become more familiar with bit-level representations of integers and floating point numbers. You’ll do this by solving a series of programming “puzzles.” Many of these puzzles are quite artificial, but you’ll find yourself thinking much more about bits in working your way through them.
2 Logistics
This is an individual project. All handins are electronic. Clarifications and corrections will be announced on Blackboard.
3 Handout Instructions
3.1 How to start
I Accept the GitHub Classroom assignment using the link: https://classroom.github.com/a/26XsGoXH
II Clone the GitHub repository created for you to a Linux machine in which you plan to do your work
(We advice you to do your work on our linux servers [linuxpool.ku.edu.tr]. See Section 8 for details.)
$ git clone https://github.com/COMP201-Fall2022/assignment-1-USER.git
(Replace USER with your GitHub username that you use to accept the assignment)
$ echo “I hereby declare that I have completed this asssignment individually, without support from anyone else.” > honor.txt
3.2 Task
There are a number of files in the directory. The only file you will be modifying and turning in is bits.c.
The bits.c file contains a skeleton for each of the 9 programming puzzles. Your assignment is to complete each function skeleton using only straightline code for the integer puzzles (i.e., no loops or conditionals) and a limited number of C arithmetic and logical operators. Specifically, you are only allowed to use the following eight operators:
! ˜ & ˆ | + << >>
A few of the functions further restrict this list. Also, you are not allowed to use any constants longer than 8 bits. See the comments in bits.c for detailed rules and a discussion of the desired coding style.
4 The Puzzles
This section describes the puzzles that you will be solving in bits.c.
4.1 Bit Manipulations
Name Description Rating Max Ops
bitXor(x,y) Implement xˆy using only ˜ and & 1 14
getByte(x,n) Extract byte n from word x 2 6
rotateLeft(x,n) Rotate x to the left by n 3 25
logicalNeg(x) Implement the logical negation without using ’!’ 4 12
Table 1: Bit-Level Manipulation Functions.
4.2 Two’s Complement Arithmetic
Table 2 describes a set of functions that make use of the two’s complement representation of integers. Again, refer to the comments in bits.c and the reference versions in tests.c for more information.
Name Description Rating Max Ops
fitsShort(x) return 1 if x can be represented as a 16-bit, two’s complement integer. 1 8
negate(x) return -x 2 5
isGreater(x,y) return 1 if x > y 3 24
Table 2: Two’s Complement Arithmetic Functions
4.3 Floating-Point Operations
Table 3 describes a set of functions that operate on the bit-level representations of floating-point numbers. Refer to the comments in bits.c and the reference versions in tests.c for more information.
Name Description Rating Max Ops
float_neg(uf) Return bit-level equivalent of expression -f for floating point f 2 10
float_f2i(uf) Return bit-level equivalent of expression (int) f for floating point f 4 30
Table 3: Floating-Point Functions. Value f is the floating-point number having the same bit representation as the unsigned integer uf.
Functions float_neg and float_f2i must handle the full range of possible argument values, including not-a-number (NaN) and infinity. The IEEE standard does not specify precisely how to handle NaN’s, and the IA32 behavior is a bit obscure. For both float_neg and float_f2i, when the argument is NaN, return the argument.
The included program fshow helps you understand the structure of floating point numbers. To compile fshow, switch to the handout directory and type:
$ make
You can use fshow to see what an arbitrary pattern represents as a floating-point number:
$ ./fshow 2080374784
Floating point value 2.658455992e+36
Bit Representation 0x7c000000, sign = 0, exponent = f8, fraction = 000000 Normalized. 1.0000000000 X 2ˆ(121)
You can also give fshow hexadecimal and floating point values, and it will decipher their bit structure.
5 Evaluation
Your score will be computed out of a maximum of 50 points based on the following distribution:
22 Correctness points.
18 Performance points.
5 Effective use of version control points.
5 Style points.
Correctness points. The 9 puzzles you must solve have been given a difficulty rating between 1 and 4, such that their weighted sum totals to 22. We will evaluate your functions using the btest program, which is described in the next section. You will get full credit for a puzzle if it passes all of the tests performed by btest, and no credit otherwise.
Performance points. Our main concern at this point in the course is that you can get the right answer. However, we want to instill in you a sense of keeping things as short and simple as you can. Furthermore, some of the puzzles can be solved by brute force, but we want you to be more clever. Thus, for each function we’ve established a maximum number of operators that you are allowed to use for each function. This limit is very generous and is designed only to catch egregiously inefficient solutions. You will receive 2 points for each correct function that satisfies the operator limit.
Effective use of version control points. You are required to push your changes to the repository frequently. If you only push the final version, even if it is implemented 100% correctly, you will lose a fraction of the grade because you are expected to learn to use Version Control Systems effectively. You do not have to push every small piece of change to Github but every meaningful change should be pushed. For example, each of the functions coded and tested can be one commit. For each function, there should be at least one commit (with proper commit message) that includes just modifications on that function.
Style points. Finally, we’ve reserved 5 points for a subjective evaluation of the style of your solutions and your commenting. Your solutions should be as clean and straightforward as possible. Your comments should be informative, but they need not be extensive.
Autograding your work
We have included some autograding tools in the handout directory — btest, dlc, and driver.pl — to help you check the correctness of your work.
• btest: This program checks the functional correctness of the functions in bits.c. To build and use it, type the following two commands:
$ make
$ ./btest
Notice that you must rebuild btest each time you modify your bits.c file.
You’ll find it helpful to work through the functions one at a time, testing each one as you go. You can use the -f flag to instruct btest to test only a single function:
$ ./btest -f bitXor
You can feed it specific function arguments using the option flags -1, -2, and -3:
$ ./btest -f bitXor -1 7 -2 10
Check the file README for documentation on running the btest program.
• dlc: This is a modified version of an ANSI C compiler from the MIT CILK group that you can use to check for compliance with the coding rules for each puzzle. The typical usage is:
$ ./dlc bits.c
The program runs silently unless it detects a problem, such as an illegal operator, too many operators, or non-straightline code in the integer puzzles. Running with the -e switch:
$ ./dlc -e bits.c
causes dlc to print counts of the number of operators used by each function. Type ./dlc -help for a list of command line options.
• driver.pl: This is a driver program that uses btest and dlc to compute the correctness and performance points for your solution. It takes no arguments:
$ ./driver.pl
6 Handin Instructions
As with Assignment 0, we use GitHub for the submissions as follows. Note that we want you to get used to using a version management system (Git) in terms of writing good commit messages and frequently committing your work so that you can get most out of Git.
I Commit all the changes you make: $ git commit -a -m “commit message”
Note: please use meaningful commit messages because
II Push your work to GitHub servers: $ git push origin main
7 Advice
• The dlc program enforces a stricter form of C declarations than is the case for C++ or that is enforced by gcc. In particular, any declaration must appear in a block (what you enclose in curly braces) before any statement that is not a declaration. For example, it will complain about the following code:
int foo(int x)
{
int a = x;
a *= 3; /* Statement that is not a declaration */ int b = a; /* ERROR: Declaration not allowed here */
}
• Use linuxpool.ku.edu.tr linux servers to test your code in order to avoid compatibility issues.
• If there is a permission error while you are trying to run a Perl script (or any script), make it executable with chmod +x {SCRIPT_NAME} command.
8 How to use linuxpool.ku.edu.tr linux servers
I Connect to KU VPN (If you are connected to the KU network, you can skip this step.)
See for details: https://confluence.ku.edu.tr/kuhelp/ithelp/it-services/network-and-wireless/vpn-access
$ ssh USER@linuxpool.ku.edu.tr
III When you are finished with your work, you can disconnect by typing: $ exit
We advice you to watch the following video about the usage of SSH, which is used to connect remote servers, and SCP, which is used to transfer files between remote servers and your local machine: https://www.youtube.com/watch?v=rm6pewTcSro

Figure 1: How to connect and disconnect using SSH
10 Late Submission Policy
Acknowledgement