Introduction to Computer Systems Homework 1

cs154: Introduction to Computer Systems

Homework 1

Submit your answers by adding and committing one file with your answers into the hw1 directory of your
CNETID-cs154-spr-20 svn repository1
.
The file should be named either hw1.txt or hw1.pdf for answers written in a plain ASCII text file, or
PDF file, respectively. PDFs of scanned hand-written pages must be clearly legible, and must not exceed 5
megabytes. No other file formats, or filenames are acceptable, and no files besides hw1.txt or hw1.pdf
will be graded. There is no need or benefit to including your name or CNetID in your HW filename. Not
following directions may result in losing points.
(Q1) 10 points
Consider the following self-contained program:
#include <stdio.h
int main() {
int foo;
char endian;
foo = 0;
endian = 0;
printf("hello world, from a %s-endian machine\n",
endian ? "big" : "little");
return endian;
}
Figure out what should be used in the assignments to foo and endian (instead of the current initializations
to zero) for the program to correctly describe the endian-ness of the machine it is running on. The assignment
to foo should be a constant, and the assignment to endian should be an expression involving foo. No
other variables or lines of code are needed. Your program should not assume anything about word size, but
you can assume int contains more than one bytes, and char has only one byte.
Write your answer like:
foo =
endian =
To get full credit you need to explain your reasoning in one or two sentences: why does this code work?
(Q2) 8 points + 2 bonus points
For questions marked with bonus, you won’t lose any point if you skip them, or answer them incorrectly, but
correct answers can help make up for the lost points in the SAME question (Q2 here). However, the total
points will not exceed the regular upper bound. For example, if you get 7 points from the regular parts (A,
B, C, D here), and 2 points from the bonus one, then your total points will be 8.
For each of the following, create C expressions involving a given int x that evaluate to 1 if and only if
the condition is true, and 0 otherwise. A “nibble” is half a byte (4 bits). Follow the bit-level integer coding
rules in the textbook, with the additional restriction that you may not use equality (==) or inequality (!=)
tests.
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see https://classes.cs.uchicago.edu/current/15400-1/svn.html
A. At least one bit of x is 1.
B. At least one bit of x is 0.
C. Any of the bits in the least significant nibble of x is 1.
D. Any odd bit of x is 1. The least-significant bit is an even bit. For this part you can assume an int is
32-bits.
(Bonus) E. Any of the bits in the most significant nibble of x is 0.
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