Re^4: pack and unpack with 8 bit integers

Hello Anonymous Monk,

First of all I want to say a big thank you for the analytic answer to my question.

You helped me to understand a lot, not only about the binary process on Perl but also how my future questions should be written so people can follow easier and sujest possible alternative solutions.

Well I am working on Simple Network Time Protocol (SNTP). I have created a simple version UDP SNTP Client/Server RFC. Where I was introduced to the idea to submit my code to CPAN library.

So I decided to add all the features and details that the RFC 2030 describes.

I have created the improved version and it seems fine from my point of view. I will post it possibly today or tomorrow to ask for possible minor improvements from all the expert Monks here.

So in order to make my script as generic as possible I wanted to follow the instructions "by letter". But to be 100% honest it would not make a difference if I have a 3 bit int "i" or 3 bit character "c". The representation is only an integer number 7. So I want to believe that it will not be a problem, with the 8 bit character that I am cutting to 3 bit. The program on both sides client and server can encode and decode the number. So I assume there is no problem about it.

Since I am not really experienced with binaries I tried to do my best, and I hope that the scripts will have minimum possible bugs.

So more or less I described my task that actually I am doing for fun while I am trying to improve my skills and keep my mind busy.

Again thank you for your time and effort answering my question and providing such an analytic answer.

Seeking for Perl wisdom...on the process of learning...not there...yet!

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Re^5: pack and unpack with 8 bit integers by Anonymous Monk on Sep 22, 2014 at 23:01 UTC
Thanks for the further information, I look forward to seeing your code. Unsigned integers of almost any size aren't a problem. You can mask a value before handing it off to pack, e.g. `pack("C", 5 & 0b111)` will get you the value 5 represented as the lowest 3 bits of the returned byte (the masking is not even necessary if you know your input is in the proper range). The inverse would be to unpack and then mask the value. It gets a little more complicated if you want signed integers, as you have to perform Sign extension as previously mentioned. In general, it is important to remember to check the range of the value you want to store, so that there are no unexpected overflows! Since I am not really experienced with binaries I tried to do my best, and I hope that the scripts will have minimum possible bugs. When in doubt, test, test, test! Your two conversion functions to and from 3-bit numbers only require 8 test cases each (plus maybe a few to check for invalid values), that's no problem to write up, and you'll have immediate certainty that your conversion functions work. Even if it sometimes gets a little annoying to write lots of test cases, they are your safety net. And with some practice it gets easier and easier to properly modularize your code so that it's more easily tested.	[reply] [d/l]
Re^6: pack and unpack with 8 bit integers by thanos1983 (Parson) on Sep 23, 2014 at 14:51 UTC
Hello Anonymous Monk, Again thank you for your time and effort reading and replying on my question. I was not aware that I could mask the value. Hmmm maybe I should take a look on it, I have never tried something similar to that. Well there is always first time for everything. Finally I manage to finalize the code and I have released it for comments from experts just like you. Here is a link to the post SNTP Client/Server V2 RFC. This is only a best version, because I guess I will have many errors that I need to take care of. When in doubt, test, test, test! If you see how many small scripts I have created just for the conversion of decimals, floating points to binary and vice versa you will laugh with me. But as you said it was the only way. Thank you again for your time and effort. Seeking for Perl wisdom...on the process of learning...not there...yet!	[reply] [d/l] [select]