CS 2505 Spring 2019
Data Lab: Data and Bitwise Operations
Assigned: March 19
Due: Tuesday March 29, 23:59
Ends: Friday April 5, 23:59
1 Introduction
The purpose of this assignment is to become more familiar with bit-level representations of integers. 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
代做CS 2505留学生作业、代做Bitwise Operations作业、代写C++实验作业、C++程序语言作业调试
Download the file datalab-handout.tarfrom the course website to a (protected) directory on a Linux
machine on 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 assigned 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 arithmetic and logical operators:
! & | + << >>
(Of course, you are allowed to use the assignment operator.) A few of the functions further restrict this list.
Also, you are not allowed to use any literal constants longer than 8 bits. See the comments in bits.c for
detailed rules and a discussion of the desired coding style.
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4 The Puzzles
This section describes the puzzles that you will be solving in bits.c.
4.1 Bit Manipulations
Table 1 describes a set of functions that manipulate and test sets of bits. The “Rating” field gives the
difficulty rating for the puzzle, the “Max Ops” field gives the maximum number of operators you are allowed
to use to implement each function, and the “Points” field shows how many points a solution to the puzzle is
worth. 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.
Name Description Rating Max
Ops Points
bitAnd(x, y) returns x & y 1 8 30
upperBits(n) pads n upper bits with 1’s 1 10 30
byteSwap(x, n, m) swaps the nth byte and the mth byte of x 2 25 25
isLess(x, y) if x < y then return 1, else return 0 3 24 15
Table 1: Required Functions
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 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
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:
unix> ./btest -f subOK
You can feed it specific function arguments using the option flags -1, -2, and -3:
unix> ./btest -f subOK -1 0xFFFFFFFF 0xFAFAFAFA
Check the file README for documentation on running the btest program.
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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 correctness and
performance points for your solution. It takes no arguments:
unix> ./driver.pl
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:
Correctness points. (maximum 80 points) The 4 puzzles you must solve have been given a difficulty rating
between 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 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 5 points for each correct 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:
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/*
* isNotMultOf4 - returns 0 if x is a multiple of 4,
* non-0 otherwise
* Examples: isMultOf4(0x033B104C) = 0
* isMultOf4(0x033B1046) != 0
* Legal ops: ? & ? |
* 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 & 0x00000003.
*
*/
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:
// 00000000 00000000 00000000 00000011.
return x & mask; // 0 if low bits are 00, non-0 otherwise
}
We will evaluate your explanations for some, but 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
below. 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
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 whether
your solution passes testing.
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7 Advice
The nature of this assignment requires creating a 32-bit executable. However, 64-bit Linux distributions,
including CentOS, do not include some libraries 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 libraries. The following
command may suffice:
> yum install glibc-devel.i686
If not, you may find the discussion below to be helpful:
stackoverflow.com/questions/23638271/how-to-compile-32-bit-apps-on-64-bit-rhel
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 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 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 */
}
The effect will be that dlc will ”zap” the offending code, and it will not compile, or will compile but
not perform correctly. 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.
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