# CS 211: Computer Architecture Homework 3: Bit Manipulation

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## Description

Introduction
This assignment is designed to give you a better understanding of bits and bit manipulation. Your task is to
write 3 small C bit-related programs. You must use bit operations to complete the task in each of the three.
You can assume all your input files will be in properly formatted.
Bit Introduction
C provides six operators for bit manipulation:
~ complement All 0 bits are set to 1 and 1 bits are set to 0.
& bitwise AND The bits in the result are set to 1 if the corresponding bits in the
two operands are both 1.
| bitwise inclusive OR The bits in the result are set to 1 if at least one of the corresponding bits in the two operands is 1.
^ bitwise exclusive OR The bits in the result are set to 1 if exactly one of the corresponding bits in the two operands is 1.
<< left shift Shifts the bits of the first operand left by the number of bits
specified by the second operand.
>> right shift Shifts the bits of the first operand right by the number of bits
specified by the second operand.
For example:
1 un si gned s h o r t x = 5 , y = 2 , z ; // i n bi n a r y 5 i s 101 and 2 i s 10
2 z = x & y ; // r e s u l t : 0
3 z = 5 | y ; // r e s u l t : 7
4 z = 5 ˆ 1 ; // r e s u l t : 4
An example using shifting:
1 un si gned s h o r t x = 5 ;
2 p r i n t f ( ”%u\n%u\n” , x << 1 , x >> 1 ) ;
First: Bit functions (35 Points)
You have to write a program that will read a number followed by a series of bit operations from a file and
perform the given operations sequentially on the number. The operations are as follows:
1
set(x, n, v) sets the nth bit of the number x to v
comp(x, n) sets the value of the nth bit of x to its complement (1 if 0 and 0 otherwise)
get(x, n) returns the value of the nth bit of the number x
The least significant bit (LSB) is considered to be index 0.
Input format: Your program will take the file name as input. The first line in the file provides the value
of the number x to be manipulated. This number should be considered an unsigned short. The following
lines will contain the operations to manipulate the number. To simplify parsing, the format of the operations will always be the command name followed by 2 numbers, separated by tabs. For the set(x, n, v)
command, the value of the second input number (v) will always be either 0 or 1. For the comp(x, n)
and get(x, n) commands the value of the second input number will always be 0 and can be ignored. Note
that the changes to x are cumulative, rather than each instruction operating independently on the original x.
Output format: Your output for comp and set commands will be the resulting value of the number x after
each operation, each on a new line. For get commands, the output should be the requested bit’s value.
Example Execution:
For example, a sample input file “file1.txt” contains the following (except the annotation comments):
5 # x = 5
get 0 0 # get(x, 0), ignoring second value (0)
comp 0 0 # comp(x, 0), ignoring second value (0)
set 1 1 # set(x, 1, 1)
The result of the sample run is:
\$ ./first file1.txt
1
4
6
Second: Bit Count functions (35 points)
In this part, you have to determine the parity of a number and the number of 1-bit pairs present in the
number. Parity refers to whether a number contains an even or odd number of 1-bits. 1-bit pairs are defined
by two adjacent 1’s without overlap with other pairs.
For example:
Number Binary sequence Parity Number of pairs
7 111 Odd 1
15 1111 Even 2
367 101101111 Odd 3
Input format: This program takes a single number as an argument from the command line. This number
should be considered as an unsigned short.
2
Output format: Your program should print either “Even-Parity” if the input has an even number of 1
bits and “Odd-Parity” otherwise, followed by a tab. Your program should then print the number of 1-bit
pairs present in the number followed by a new line character.
Example Execution:
\$ ./second 12
Even-Parity 1
\$ ./second 31
Odd-Parity 2
Third: Bit Pattern function (30 points)
In this part, you have to determine whether a number’s bit representation is a palindrome. A palindrome is
defined as a sequence that is the same both forwards and backwards.
We will be working with unsigned shorts which are 2 bytes or 16 bits. For example the number 384 has the
binary sequence 0000000110000000 and is thus a palindrome while the sequence 0100100010111011 is not.
Note that all values should be considered 16-bit, so while 5 is 101 in binary and looks like a palindrome, in
16 bits it’d be 0000000000000101, which is not.
You can and should use the same get(x, n) function that you created in part 1.
Input format: This program takes a single number as an argument from the command line. This number
should be considered as an unsigned short.
Output format: Your program should print either “Is-Palindrome” if the input is a palindrome and
“Not-Palindrome” otherwise, followed by a new line character.
Example Execution:
Some sample runs and results are:
\$ ./third 5
Not-Palindrome
\$ ./third 384
Is-Palindrome
\$ ./third 1001
Not-Palindrome
3
Submission
Your submission should be a tar file named hw3.tar that contains your hw3 folder (and names are case
sensitive):
hw3
Makefile
first.c
second.c
third.c
To create this file, put everything that you are submitting into a directory named hw3. Then, cd into the
directory containing hw3 (that is, hw3’s parent directory) and run the following command:
tar cvf hw3.tar hw3
The hw3 directory in your tar file must contain 3 subdirectories, one each for each of the parts. The name of
the directories should be named first through third (in lower case). Each directory should contain a C source
file, a header file (if necessary) and a make file. For example, the subdirectory first will contain, first.c, first.h
and Makefile (the names are case sensitive).
the following command will create the autograder folder.
There are two modes available for testing your assignment with the Autograder.
First mode
Testing when you are writing code with a hw3 folder
(1) Lets say you have a hw3 folder with the directory structure as described in the assignment.
(2) Copy the folder to the directory of the autograder
(3) Run the autograder with the following command