Computer Organization (CSC 252) Spring 2019

Assignment 1: Datalab

If you want to use slip days you have to tell us beforehand. We won't assume slip days for late submissions.

Update

If you downloaded/copied the handout tarball before 8:00PM, 1/24, please download/copy it again as we have updated it. Ironically, we made this update because the compiler on the CSUG machine just got slightly smarter and we had to make the code dumber so that it does what it's supposed to do.

Introduction

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 on this assignment. In case of the latter, only one submission is needed.

Due Dates

For the trivia assignment: 11:59pm, Friday, January 25.
For the main assignment: 11:59pm, Friday, February 1.

Getting Started

We are providing you with a skeleton code file and testing utilities. To obtain these, download this to a (protected) directory on the CSUG machine in which you plan to do your work. Alternatively, you may copy it from /u/cs252/labs19/datalab/datalab-handout.tar

Then type the command:

tar xvf datalab-handout.tar

to the shell. This will cause twelve files to be created in your directory:

README
Makefile
bits.h
btest.h
bits.c
btest.c
decl.c
fshow.c
ishow.c
tests.c
driver.pl
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:

    ./btest

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.

Grading

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

Advice

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

      ./driver.pl

Trivia Assignment

The Trivia assignment is designed mainly to get your familiar with the development environment on the CSUG machine and to get you start thinking about the assignment.

Run the following program.

#include <stdio.h>

int main(int argc, char *argv[]){
    int bitPattern1 = 0x10011001;
    int bitPattern2 = 0x01100110;
    int bitPattern3 = 0xFFFFFFFF;
    int bitPattern4 = 0x00000000;

    /* pair 1 */
    printf("bitPattern1 &  bitPattern2 = %x\n", bitPattern1 &  bitPattern2);
    printf("bitPattern1 && bitPattern2 = %x\n", bitPattern1 && bitPattern2);

    /* pair 2 */
    printf("bitPattern1 |  bitPattern2 = %x\n", bitPattern1 |  bitPattern2);
    printf("bitPattern1 || bitPattern2 = %x\n", bitPattern1 || bitPattern2);

    /* pair 3 */
    printf("bitPattern1 &  bitPattern3 = %x\n", bitPattern1 &  bitPattern3);
    printf("bitPattern1 && bitPattern3 = %x\n", bitPattern1 && bitPattern3);

    /* pair 4 */
    printf("bitPattern1 |  bitPattern3 = %x\n", bitPattern1 |  bitPattern3);
    printf("bitPattern1 || bitPattern3 = %x\n", bitPattern1 || bitPattern3);

    /* pair 5 */
    printf("bitPattern2 &  bitPattern4 = %x\n", bitPattern2 &  bitPattern4);
    printf("bitPattern2 && bitPattern4 = %x\n", bitPattern2 && bitPattern4);

    /* pair 6 */
    printf("bitPattern2 |  bitPattern4 = %x\n", bitPattern2 |  bitPattern4);
    printf("bitPattern2 || bitPattern4 = %x\n", bitPattern2 || bitPattern4);

    return 0;
}

Write the values of the four bitpatterns in binary notation.
Why do the two outputs differ for pairs 1, 2, 3, 4, and 6?

What is the output when the following program runs on a CSUG Linux machine? Why would the output be different if the program were run on a PowerPC-based game console or an old Apple Macintosh?

#include <stdio.h>
int main(int argc, char *argv[]){
    int *translation;
    char bytearray[4];

    bytearray[0] = 0x00;
    bytearray[1] = 0x00;
    bytearray[2] = 0xFF;
    bytearray[3] = 0xFF;

    translation = (int*) &bytearray;
    printf("Bit pattern 0x00FF = %d.\n", *translation);
    return 0;
}

How many lines long is the original bits.c file?
What does btest print when compiled and run with the original bits.c file?

What/how to turn in

The trivia assignment will be submitted via Blackboard. The main assignment will be submitted using the command:

    /u/cs252/bin/TURN_IN .

Note that there's a dot in that command! Make sure you are in the directory that contains bits.c when running the above script. Watch Blackboard for any clarifications or revisions to the assignment.

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 (there is no separate README file for this assignment)