Homework 3, The Sieve File.

Short Description:

Goals

• Employed open, read, write, close and lseek.

Formal Description

• Initialize a file of length n (give or take), to a given character. This is a simple write loop. This loop must use the write system call.
• Set current prime to 2
• While the current prime is less than or equal to the square root of n
  • Cross off all multiples of the current prime with a different character. This must include at least one lseek and write system calls.
  • Starting at the current prime + 1, find the next value not crossed off. Make this the current prime. This must be done with lseek and write.
• Starting again at 2, print out all values that have not been "crossed off".

Discussion

• You must do your computations in a file, not an array, vector, map, list, ...
• You may not use iostreams or c style FILEs. All file I/O must be done via read/write.
• If you wish, you may work at the bit level using &, |, ^, and ~. This way, your file will be $\lceil \frac{n}{8} \rceil$ bytes long instead of n, but your work will be way more complex.
  • I will give up to 50% extra credit for this technique. If you do this, please note this in a README file in your submission.
  • I did not do this, I think it might not be too hard but ...
• If you wish, you may visualize your result by producing an image file.
  • You may choose a value for n which factors nice (200x2000 for example).
  • This must all be done as part of your program.
  • You may use the "system" system call to execute commands such as cat, cp, ...
  • You must use the output of the first part directly, ie add a header or footer to this file, you may not rewrite the file.
  • In this portion of your program only, you may use iostream, fstreams, or FILES.
  • I made a net pbm file then called pbmtopng to convert it to a usable image file.
  • Yes, Chris, you can write a svg file if you wish, the rest of you, can write a jsascript interpreter which will load your file and display it.
  • here is my picture.
  • See these examples.
  • I will give up to 25% extra credit for this visualization. If you do this, please note this in a README file in your submission.
• If you do anything else you believe is worthy of extra credit, note it in a README file in your submission.

Required Files

Submission