Data Lab #

This is likely the first lab students should do. Quoting from the assignment write-up, the “purpose of this assignment is to become more familiar with bit-level representations of integers and floating point numbers.” Chapter Two is the chapter concerned with this area.

Contents #

• Files downloaded from CS:APP website as datalab-handout.tar, and listed below in the original README contents

Lab Assignment Write-Up #

csapp.cs.cmu.edu/3e/datalab.pdf.

This write-up is very helpful for even those doing self-study. Read through it to learn how to approach this lab’s problem(s).

Original README.md #

***********************
The CS:APP Data Lab
Directions to Students
***********************

Your goal is to modify your copy of bits.c so that it passes all the tests in btest without violating any of the coding guidelines.

0. Files: #

• Makefile - Makes btest, fshow, and ishow
• README - This file
• bits.c - The file you will be modifying and handing in
• bits.h - Header file
• btest.c - The main btest program
  • btest.h - Used to build btest
  • decl.c - Used to build btest
  • tests.c - Used to build btest
  • tests-header.c - Used to build btest
• dlc* - Rule checking compiler binary (data lab compiler)
• driver.pl* - Driver program that uses btest and dlc to autograde bits.c
• Driverhdrs.pm - Header file for optional “Beat the Prof” contest
• fshow.c - Utility for examining floating-point representations
• ishow.c - Utility for examining integer representations

1. Modifying bits.c and checking it for compliance with dlc #

IMPORTANT: Carefully read the instructions in the bits.c file before you start. These give the coding rules that you will need to follow if you want full credit.

Use the dlc compiler (./dlc) to automatically check your version of bits.c for compliance with the coding guidelines:

   unix> ./dlc bits.c

dlc returns silently if there are no problems with your code. Otherwise it prints messages that flag any problems. Running dlc with the -e switch:

	unix> ./dlc -e bits.c  

causes dlc to print counts of the number of operators used by each function.

Once you have a legal solution, you can test it for correctness using the ./btest program.

2. Testing with btest #

The Makefile in this directory compiles your version of bits.c with additional code to create a program (or test harness) named btest.

To compile and run the btest program, type:

unix> make btest
unix> ./btest [optional cmd line args]

You will need to recompile btest each time you change your bits.c program. When moving from one platform to another, you will want to get rid of the old version of btest and generate a new one. Use the commands:

unix> make clean
unix> make btest

Btest tests your code for correctness by running millions of test cases on each function. It tests wide swaths around well known corner cases such as Tmin and zero for integer puzzles, and zero, inf, and the boundary between denormalized and normalized numbers for floating point puzzles. When btest detects an error in one of your functions, it prints out the test that failed, the incorrect result, and the expected result, and then terminates the testing for that function.

Here are the command line options for btest:

unix> ./btest -h
Usage: ./btest [-hg] [-r <n>] [-f <name> [-1|-2|-3 <val>]*] [-T <time limit>]
    -1 <val>  Specify first function argument
    -2 <val>  Specify second function argument
    -3 <val>  Specify third function argument
    -f <name> Test only the named function
    -g        Format output for autograding with no error messages
    -h        Print this message
    -r <n>    Give uniform weight of n for all problems
    -T <lim>  Set timeout limit to lim

Examples:

Test all functions for correctness and print out error messages: unix> ./btest

Test all functions in a compact form with no error messages: unix> ./btest -g

Test function foo for correctness: unix> ./btest -f foo

Test function foo for correctness with specific arguments: unix> ./btest -f foo -1 27 -2 0xf

Btest does not check your code for compliance with the coding guidelines. Use dlc to do that.

3. Helper Programs #

We have included the ishow and fshow programs to help you decipher integer and floating point representations respectively. Each takes a single decimal or hex number as an argument. To build them type:

unix> make

Example usages:

unix> ./ishow 0x27
Hex = 0x00000027,	Signed = 39,	Unsigned = 39

unix> ./ishow 27
Hex = 0x0000001b,	Signed = 27,	Unsigned = 27

unix> ./fshow 0x15213243
Floating point value 3.255334057e-26
Bit Representation 0x15213243, sign = 0, exponent = 0x2a, fraction = 0x213243
Normalized.  +1.2593463659 X 2^(-85)

linux> ./fshow 15213243
Floating point value 2.131829405e-38
Bit Representation 0x00e822bb, sign = 0, exponent = 0x01, fraction = 0x6822bb
Normalized.  +1.8135598898 X 2^(-126)