datalab.dvi
CS 2505 Spring 2022
Data Lab: Data and Bitwise Operations
Assigned: March 25
Due: April 5, 23:59
Ends: April 8, 23:59
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
You may work in pairs for this assignment. If you work with a partner, list both names and both PIDs in a
comment at the beginning of the bits.c file you submit.
3 Handout Instructions
Start by downloading the datalab-handout.tar to a (protected) directory on a Linux machine in
which you plan to do your work. Then give the command
unix> tar xvf datalab-handout.tar.
This will cause a number of files to be unpacked 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 13 programming puzzles. Your assignment is to
complete each function skeleton using only straightline code for the integer puzzles (i.e., no loops or con-
ditionals) and a limited number of C arithmetic and logical operators. Specifically, you are only allowed to
use the following eight operators:
1
! ˜ & ˆ | +
A few of the functions further restrict this list. Also, you are not allowed to use any constants longer than 8
its. 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.
Table 1 lists the puzzles in rought order of difficulty from easiest to hardest. The “Rating” field gives the
difficulty rating (the number of points) for the puzzle, and the “Max ops” field gives the maximum numbe
of operators you are allowed to 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 co
ect behavior of your functions, although they don’t satisfy
the coding rules for your functions.
Name Description Rating Max Ops Points
itXor(x,y) x || y using only & and ˜ XXXXXXXXXX
isEqual(x,y) return 1 if x == y and 0 otherwise XXXXXXXXXX
eplaceByte(x,n,c) Replace byte n in x with c XXXXXXXXXX
isNonZero(x) Check whether x is nonzero using legal operators except ! XXXXXXXXXX
Table 1: Required Functions
(Note: the point values shown above include 5 points for evaluating performance.)
5 Evaluation
Autograding your work
We have included some autograding tools in the handout directory — btest, dlc, and driver.pl —
to help you check the co
ectness of your work.
• btest: This program checks the functional co
ectness of the functions in bits.c. To build and
use it, type the following two commands:
unix> make
unix> .
test
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:
2
unix> .
test -f subOK
You can feed it specific function arguments using the option flags -1, -2, and -3:
unix> .
test -f subOK -1 0xFFFFFFFF 0xFAFAFAFA
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> ./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:
unix> ./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 co
ectness and
performance points for your solution. It takes no arguments:
unix> ./driver.pl
Note well: Your instructors will use driver.pl to evaluate your solution. If your code does
not compile when tested with driver.pl you will receive a 0 for the assignment.
Scoring rules
Your score will be computed out of a maximum of 100 points based on the following distribution:
Co
ectness points. (maximum 80 points) The 4 puzzles you must solve have been given a difficulty rating
etween 1 and 3. Each of the puzzles will be worth the number of points shown in the tables above, but the
5 points for each puzzle will be reserved for performance. 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 driver.pl, and no credit otherwise.
Performance points. (maximum 20 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
ute 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 fo
each function. This limit is very generous and is designed only to catch egregiously inefficient solutions.
You will receive 5 points for each co
ect function that satisfies the operator limit.
Explanation and analysis points. (maximum deduction 40 points) You must add to the header comment
for each function an explanation of the logic employed in your solution. This comment must be accurate,
precise and complete. For example:
3
*
* isNotMultOf4 - returns 0 if x is a multiple of 4,
* non-0 otherwise
* Examples: isMultOf4(0x033B104C) = 0
* isMultOf4(0x033B1046) != 0
* Legal ops: ˜ & ˆ |
* Max ops: 5
* Rating: 1
* Logic:
* x is a multiple of 4 if and only if x % 4 = 0. But, since
* x % 4 returns the remainder when x is divided by 4, and
* dividing by 4 will simply chop off the two low bits of x,
* x % 4 will yield the two low bits of the representation
* of x. So, x is a multiple of 4 if and only if its
* representation ends in two 0s.
*
* We can obtain the desired bits by applying the right
* mask to x. The key is to set the 30 high bits to 0,
* so we could do this: x & 0x XXXXXXXXXX.
*
*
int isMultOf4(int x) {
int mask = 0x03;
OK, it’s a one-byte constant ’0011’,
which will be sign-extended to a
32-bit value:
XXXXXXXXXX XXXXXXXXXX.
eturn x & mask;
0 if low bits are 00, non-0 otherwise
}
The explanation must be written in the header comment for the function, not merely embedded in comments
in the body of the function. A good explanation will not resort to merely describing code, but it is acceptable
to cite individual statements if that clarifies your explanation.
We will evaluate your explanations for some, but perhaps not all, of the functions. If your explanation for a
function is unsatisfactory, we will apply a deduction of up to 10 points to your score for that function.
The evaluation of these comments will be performed by the TAs, not by the autograding tools described
elow. It is up to you to make sure your explanations are worthy of credit.
6 Handin Instructions
You will submit your bits.c file to the Curator under the heading c06. Like the earlier programming
assignments, this is not autograded at the time of submission. Instead, we will periodically run autograding
4
code on your submissions, and post the results to the Curator system.
Of course, if you apply the tools btest, dlc, and driver.pl properly, you will already know whethe
your solution passes testing.
7 Advice
• The nature of this assignment requires creating a 32-bit executable. However, 64-bit Linux distribu-
tions, including CentOS, do not include some li
aries that are necessary to build a 32-bit executable.
That leaves you with two choices.
You can complete the assignment on a node in the rlogin cluster, which do support 32-bit builds.
Or, you can update your CentOS virtual machine to include the necessary li
aries. The following
command may suffice:
yum install glibc-devel.i686
If not, you may find the discussion below to be helpful:
stackoverflow.com/questions/ XXXXXXXXXX/how-to-compile-32-bit-apps-on-64-bit-rhel
• Don’t include the
header file in your bits.c file, as it confuses dlc and results in
some non-intuitive e
or messages. You will still be able to use printf in your bits.c file fo
debugging without including the header, although gcc will print a warning that you
can ignore.
• The dlc program enforces an archaic form of the C Standard. In particular, its rules for declarations
are different than those enforced by gcc. In particular, any declaration must appear in a block (what
you enclose in curly
aces) before any statement that is not a declaration. For example, it will
complain about the following code:
int foo(int x)
{
int mask = 0x7F; /* Declaration, OK *
int a = x & mask; /* Statement involving a declaration, OK *
a = a
4; /* Statement, not a declaration, OK *
int b = ˜x; /* E
or: declaration not allowed here *
eturn ( a | b); /* E
or after previous line is zapped *
}
The effect will be that dlc will ”zap” the offending code, and it will not compile, or will compile but
not perform co
ectly. You can avoid lots of disappointment if you make sure you use driver.pl
to do the final testing of your solution.
We will make no accommodations for failing to test your solution with driver.pl; you have been
warned.
5
• Write a simple, stand-alone driver for each of your function solutions, and try testing the logic of you
solutions manually. All that is needed is a main() function that passes test values to your function
and prints the results. For example:
#include #include int getByte(int x, int n);
int main(int argc, char** argv) {
if ( argc != 2 ) {
printf("Invocation: driver \n");
printf(" e.g., driver 8B320CF1\n");
eturn 1;
}
Interpret the command-line parameter, which is assumed to