C编程代写代做、代做Manipulating Bits

日期：2018-04-21 08:46

CSCE 231, Fall 2017

Lab 2: Manipulating Bits (Data Lab)

Assigned: Sep. 11

Due: Sept. 22 on or before 11:59PM.

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

This is an individual project. All submissions are electronic. Clarifications and corrections will be posted

on the course Web page.

3 Handout Instructions

Start by copying datalab-handout.tar from canvas to a (protected) directory on csce.unl.edu in

which you will do your work. Note that you must use csce.unl.edu to do this work. You can login to

csce.unl.edu by using the same login information as that used to login to cse.unl.edu. Once you have copied

the file to csce.unl.edu, give the following command to unpack the provided archive file:

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 15 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 operators:

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! ˜ & ˆ | + << >>

A few of the functions further restrict this list. 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.

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 (the number of points) for the puzzle, and the “Max ops” field gives the maximum number

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 correct behavior of your functions, although they don’t satisfy

the coding rules for your functions.

Name Description Rating 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

bang(x) Compute !n without using ! operator. 4 12

Table 1: Bit-Level Manipulation Functions.

4.2 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.

5 Evaluation

Your score will be computed out of a maximum of 72 points based on the following distribution:

42 Correctness points.

30 Performance points.

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Name Description Rating 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/2

n 2 15

negate(x) -x without negation 2 5

isPositive(x) x > 0? 3 8

isLessOrEqual(x,y) x <= y? 3 24

isAsciiDigit(x) 0x30 <= x <= 0x39? 3 15

isNonZero(x) x != 0? 4 10

howManyBits(x) Compute the number of bits required to 4 90

represent x in two’s complement

ilog2(x) Compute ⌊log2

(x)⌋ 4 90

Table 2: Arithmetic Functions

Correctness points. The 15 puzzles you must solve have been given a difficulty rating between 1 and 4, such

that their weighted sum totals to 40. 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 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. 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 two points

for each correct function that satisfies the operator limit.

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 bitAnd

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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> ./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 TAs will use driver.pl to evaluate your solution.

6 Handin Instructions

Submit your bits.c solution file via canvas after you are done. This must be submitted by September 22,

11:59pm.

7 Advice

• 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. 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:

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int foo(int x)

{

int a = x;

a *= 3; /* Statement that is not a declaration */

int b = a; /* ERROR: Declaration not allowed here */

}