Project 1 : manipulating bits

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CSCI 247 Computer Systems I
Project 1 : manipulating bits
The purpose of this assignment is to become more familiar with bit-level representations of integers and
floating point numbers. You will solve a series of programming tasks, some of which are quite trivial, but
others are indeed implementations of often-used tasks that are part of important applications for
network procedures, calculating distances, etc.
Outcome
The goal is for you to find yourself thinking much more about bits in working your way through the
programming tasks.
As with the other parts of this class, you can work in groups of two, or solo. However, you are NOT
allowed to work in groups of 3 or more, and groups cannot communication solutions nor approaches
with other groups.
Files
Download from the files section of Canvas the project 1 zip file, and move it to your CS account. Use
sftp, or an ftp client such as FileZilla. Unzip it via unzip project1_manipulatingBits.zip
Implementation Details
The only file you will be modifying and turning in is bits.c.
The bits.c file contains a skeleton for each of several programming tasks (functions). Your assignment is
to complete each function skeleton using only straight-line code for the integer puzzles (i.e., no loops
nor conditionals) and a limited number of C arithmetic and logical operators. Specifically, you are
only allowed to use the following eight operators:
! ~ & ^ | + << >>
A few of the functions in bits.c further restrict this list, so read closely the comments for each function.
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.
Important: Carefully read the instructions in the bits.c file before you start. These give the coding rules
that you will need to follow.
Hint: The comments for each function also provide a hint, which mentions approximately how many
lines of code a good solution might require. That is not to imply that your solution must use that few
number of lines of code, but if you find yourself writing far more than that many lines of code,
perhaps you are overthinking it and you should step back and brainstorm.
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CSCI 247, project 1 Filip Jagodzinski, Summer 2020
The Puzzles (tasks, functions)
There are 3 types of puzzles: Bit manipulation, Two’s Complement, and Floating Point Manipulations.
This section describes the puzzles that you will be solving in bits.c.
Bit Manipulations
Table 1 describes a set of functions that manipulate and test bit patterns. The Difficulty field gives the
difficulty rating (the number of points) for the puzzle, and the Max ops field gives the maximum number
of operators you can use to implement each function. See the comments in bits.c for more details on
the desired behavior of the functions. You may also refer to the test functions in tests.c. These are used
as reference functions to express the correct behavior of your functions, although they don't satisfy the
coding rules for your functions.
Table 1: Bit-Level Manipulation Functions.
Function name Description Difficulty Max Ops
bitAnd(x,y) x & y using only | and ~ 1 8
getByte(x,n) Get byte n from x 2 6
logicalShift(x,n) Shift right logical 3 20
bitCount(x) Count the number of 1's in x. 4 40
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.
Table 2: Arithmetic Functions
Function name Description Difficulty Max Ops
tmin() Most negative two's complement integer 1 4
fitsBits(x,n) Does x fit in n bits? 2 15
divpwr2(x,n) Compute x/2n 2 15
negate(x) -x without negation 2 5
isPositive(x) x > 0? 3 8
ilog2(x) Compute log2(x) 4 90
Floating-Point Operations
For this part of the assignment, you will implement some common single-precision floating-point
operations. You can use standard control structures (conditionals, loops), and you may use both int and
unsigned data types, including arbitrary unsigned and integer constants. You may not use any unions,
structs, or arrays. Most significantly, you may not use any floating point data types, operations, or
constants. Instead, any floating-point operand will be passed to the function as having type unsigned,
and any returned floating-point value will be of type unsigned. Your code should perform the bit
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CSCI 247, project 1 Filip Jagodzinski, Summer 2020
manipulations that implement the specified 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.
Table 3: Floating-Point Functions. Value f is the floating-point number having the same bit
representation as the unsigned integer uf.
Function name Description Difficulty Max Ops
float_neg(uf) Compute -f 2 10
float_twice(uf) Computer 2*f 4 30
Functions float_neg and float_twice 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. We will follow a convention that for any function
returning a NaN value, it will return the one with bit representation 0x7FC00000. The provided program
fshow helps you understand the structure of floating point numbers. To compile fshow, type:
unix> make
You can use fshow to see what an arbitrary pattern represents as a floating-point number:
unix> ./fshow 2080374784
Floating point value 2.658455992e+36
Bit Representation 0x7c000000, sign = 0, exponent = f8, fraction = 000000
Normalized. 1.0000000000 X 2^(121)
You can also give fshow hexadecimal and floating point values, and it will decipher their bit structure.
Auto-grading your work
You are being provided some autograding tools -- 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:
unix> make
unix> ./btest

The make program is an industry/CS standard macro-like approach for compiling and linking programs,
which otherwise you’d need to do manually via the command line.
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CSCI 247, project 1 Filip Jagodzinski, Summer 2020
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:
unix> ./btest -f bitAnd
You can feed it specific function arguments using the option flags -1, -2, and -3:
unix> ./btest -f bitAnd -1 7 -2 0xf
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:
unix> /home/clausoa/bin/dlc bits.c
This command will invoke the dlc program, that is in the /home/clausoa/bin directory.
The program runs silently unless it detects a problem, such as an illegal operator, too many operators, or
non-straight-line code in the integer puzzles. Running with the -e switch:
unix> /home/clausoa/bin/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.
NOTE: dlc is installed in Dr. Clauson’s personal bin directory. If you want to simplify your life, you can
add that bin directory to your PATH variable (google bash PATH) or create an alias (google bash alias).
driver.pl
This is a driver program that uses btest and dlc to compute the correctness and performance points for
your code. It will compile your bits.c file, and test each of your functions. The driver.pl program takes no
arguments:
unix> ./driver.pl
The driver.pl program will be used to evaluate your solution.
If you get an execution error, you might need to grant execution rights to the driver.pl program. To do
that, you would issue the following (which also gives read and write permissions):
unix> chmod u+rwx driver.pl
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CSCI 247, project 1 Filip Jagodzinski, Summer 2020
Technical caveats
• Don't include the <stdio.h> header file in your bits.c file, as it confuses dlc and results in
some non-intuitive error messages. You will still be able to use printf in your bits.c file for
debugging without including the <stdio.h> header, although gcc will print a warning that
you can ignore.
• The dlc program enforces a stricter form of C declarations than is the case for C++ or that is
enforced by gcc. Any declaration must appear in a block (what you enclose in curly braces)
before any statement that is not a declaration. In other words, for each function you must
declare all your variables first. 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
}

Rubric and Submission
Upload your bits.c file to Canvas. Important: If you are not able to complete one or more of the puzzles
(functions), then do not upload a bits.c file that does not compile. Instead, simply keep the original
version of that function (the one that returns 2).
Correctness points. The 12 puzzles are assigned a difficulty rating between 1 and 4, such that their
weighted sum totals 30. Your functions will be evaluated using the btest program. You will get full credit
for a puzzle if it passes all 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. 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 can use for each function. This limit is very
generous and is designed only to catch egregiously inefficient solutions. You will receive two points for
each correct function that satisfies the operator limit.
Style points. 6 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.
Item Points
Correctness (difficulty level points for each puzzle 30
Performance (using maximum count of operators) 24
Formatting and Style 6