Assignment 1: Datalab

If you want to use slip days you have to tell us before the deadline (by emailing Sudhanshu Gupta and Shuang Zhai). We won't by default assume slip days for late submissions.

If you code does not compile on the CSUG machine, you get a 0.


The purpose of this assignment is to become more familiar with representing and manipulating data as bits.  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. 

You can choose to work individually or in pairs (2 people) on this assignment.  In case of the latter, only one submission is needed.

Due Dates

11:59 pm, Friday, Jan. 31. 

Getting Started

We are providing you with a skeleton code file and testing utilities.  To obtain these, type the command:

cp /u/cs252/labs20/datalab/datalab-handout.tar .
which copies the files to your current directory on the CSUG machine.

Then type the command:

tar xvf datalab-handout.tar
to the shell.  This will cause twelve files to be created in your directory:
  • Makefile
  • bits.h
  • btest.h
  • bits.c
  • btest.c
  • decl.c
  • fshow.c
  • ishow.c
  • tests.c
  • dlc

The only file you will be modifying is bits.c.  All other files should be left as-is.  The file btest.c allows you to evaluate the functional correctness of your code.  The file README contains additional documentation about btest.  Use the command:
    make btest 
to generate the test code and run it with the command:

Looking at the file bits.c you'll notice a C stucture team into which you should insert information identifying yourself.  Do this right away so you don't forget. 

The bits.c file also contains a skeleton for each of the 15 programming puzzles.  Your assignment is to complete each function skeleton using only straightline code (i.e., no loops or conditionals) and a limited number of C arithmetic and logical operators.  Specifically, you are allowed to use only the following eight operators:

 ! ~ & ^ | + << >> 
A few of the functions further restrict this list.  See the comments in bits.c for detailed rules and a discussion of the desired coding style.  Note also that casts and arrays are not allowed, that you may only declare variables of type int, and that you may only initialize variables to values in the range 0L - 255L


Your code will be compiled with gcc and run and tested on one of the CSUG Linux machines.  Your score will be computed out of a maximum of 78 points based on the following distribution:

(43) Correctness
(30) Performance
based on the number of operators used in each function
(5) Style
based on the TAs' subjective evaluation of the quality of your solutions and your comments

The 15 puzzles you must solve have been given a difficulty rating between 1 and 4, such that their weighted sum totals to 43.  We will evaluate your functions using the test arguments in btest.c.  You will get full credit for a puzzle if it passes all of the tests performed by btest.c, half credit if it fails one test, and no credit otherwise. 

Regarding performance, our main concern at this point in the course is that you 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 function that satisfies the operator limit. 

Finally, we've reserved 5 points for a subjective evaluation of the style of your solutions and your commenting.  Your solutions should be as clean and straightforward as possible.  Your comments should be informative, but they need not be extensive. 

Project Details

Part I: Bit Manipulations

Function Description Rating Max Ops
bitXor(x,y) (x^y) using only ~ and & 1 14
oddBits() Return word with all odd-numbered bits set to 1. 2 8
reverseBytes(x) Reverse the bytes of x. 3 25
rotateRight(x,n) Rotate x to the right by n. 3 25
bitCount(x) Returns count of number of 1's in word. 4 40

The table above describes a set of functions that manipulate and test sets of bits.  The "rating" field gives the difficulty rating (and thus 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. 

Part II: Two's Complement Arithmetic

Function Description Rating Max Ops
tmax() Return maximum two's complement integer. 1 4
addOK(x,y) Determine if can compute x+y without overflow. 3 20
rempwr2(x,n) Compute x%(2n), for 0 <= n <= 30. 3 20
satMul2(x) Multiplies by 2, saturating to Tmin or Tmax if overflow. 3 20
isGreater(x,y) If x>y then return 1, else return 0. 3 24
multFiveEighths(x) Multiplies by 5/8 rounding toward 0. 3 12
isNonZero(x) Check whether x is nonzero using the legal operators except !. 4 10

The table above describes a set of functions that make use of the two's complement representation of integers.  The "rating" and "max ops" fields have the same meaning as in Part I. 

Part III: Floating Point Operations

Function Description Rating Max Ops
float_abs(uf) Return bit-level equivalent of absolute value of f. 2 10
float_f2i(uf) Return bit-level equivalent of expression (int) f. 4 30
float_half(uf) Return bit-level equivalent of expression 0.5*f. 4 30

The table above describes a set of functions that operate on the bit-level representations of (single-precision) floating-point numbers.  The "rating" and "max ops" fields have the same meaning as in Part I. 

In this section, you are allowed to use standard control structures (conditionals, loops, and you may use both int and unsigned data types, including arbitrary unsigned and integer constants.  You may not use any unions, structs, or arrays.  Most significantly, you may not use any floating point data types, operations, or contants. 

You can use fshow to see what an arbitrary pattern represents as a floating-point number, e.g.

   		./fshow 2080374784 


You are welcome to do your code development using any system or compiler you choose.  Just make sure that the version you turn in compiles and runs correctly on the CSUG Linux machines.  If it doesn't compile, we can't grade it. 

The dlc program, a modified version of an ANSI C compiler, will be used to check your programs for compliance with the coding style rules.  You can also use it to measure the operator counts of your functions.  You can run these tests by executing the command:

       ./dlc -e bits.c 
The program runs only on the CSUG Linux machines. 

Check the file README for documentation on running the btest program.  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, e.g.,

      ./btest -f bitXor 

The is a program that uses both btest and dlc. It takes no arguments.


What/how to turn in

First make sure you are in the directory that contains bits.c. The main assignment can be submitted using the command:

    /u/cs252/bin/TURN_IN . 
Note that there's a dot in that command!  Watch Blackboard for any clarifications or revisions to the assignment. 

The TURN_IN script will ask you for your partner's ID. If you work by yourself, simply press enter; otherwise type his/her netid. Before running the TURN_IN script, be sure that you have

  • included your full name(s) and email address(es) at the top of bits.c
  • removed any extraneous print statements
  • included any appropriate commentary on your code as C comments in bits.c.