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Poll: How many programmers don't know about bit-wise operations?

news.ycombinator.com

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Re: Poll: How many programmers don't know about bit-wise operations?

#71

Post by dspeyer »

shdon wrote: post #13

((width * bytes_per_pixel)+3&~3) anyone? Can't remember how many times I've done that for Windows bitmap stride. WORD/DWORD/QWORD alignment was something I had to do frequently in C or C++ code. Even fixed point math for speed in the really old days.

That's a code snippet where extra parenthesis might help. The first several times I read it as:

    ((width * bytes_per_pixel)+(3&~3))
and thought "what's the point?"

I don't know why bitwise ops are so low precedence. They've always felt more like multiplication to me.

Re: Poll: How many programmers don't know about bit-wise operations?

#72

Post by PommeDeTerre »

fakeer wrote: post #65
philsnow wrote: post #16

I've found that people who list any of the following on their resume are way more likely to know how to bitwise their way out of a paper bag: - C (not "C/C++", those people generally mean "C++") - video codecs - compression of any kind - encryption / cryptography of any kind - embedded anything

>> those people generally mean "C++" I've never worked on C++(as in on commercial project or in a C++ team) however I've always mentioned it on my resume as C/C++, because I've worked on C(Kernel wrt Android and a little bit more) but for C++ I've only built one academic project(very minor) during UG and also took (2nd yr) DS in C++. I just do not want to miss a good job offer which requires C++. Because in the inter…

No offense is meant, but I think you're doing yourself and potential employers a disservice by listing C++ on your resume when, based on your description, you have essentially no real-world experience with it.

There is much, much more to writing solid, production-grade C++ code than could ever be learned during a minor academic project and a single undergraduate data structures course. This is especially true with the many changes brought on recent by C++11, as well as developments within the Boost camp.

It's one thing to leave C++ unlisted on your resume, and to then bring it up during an interview. But it seems, at least to me, wrong to list it without actually having the experience (be it open source projects or past commercial work) to back up the claim.

Re: Poll: How many programmers don't know about bit-wise operations?

#73

Post by huhtenberg »

philsnow wrote: post #16

I've found that people who list any of the following on their resume are way more likely to know how to bitwise their way out of a paper bag: - C (not "C/C++", those people generally mean "C++") - video codecs - compression of any kind - encryption / cryptography of any kind - embedded anything

> C (not "C/C++", those people generally mean "C++")

Bzzzt... that'd be the "C++/C" people. Those who word it as "C/C++" typically meant C with reluctant C++ if pressed.

Re: Poll: How many programmers don't know about bit-wise operations?

#74

Post by huhtenberg »

daeken wrote: post #34
jared314 wrote: post #23

I have always wondered why I was taught binary as if they were arrays, but programming languages never allowed me to use bits like arrays. It's always masking and shifting uint16_t or int32_t, instead of what I really want, "result = bits[3] xor bits2[3]".

You can do this with bit field structs in C: http://www.cs.cf.ac.uk/Dave/C/node13.html Super handy when you're dealing with oddly packed int representations and such.

You would think so, but - No, there are no bitfield arrays. You can't have -

  struct octet
  {  
    int bit:1 [8];
  };
which is what the OP is asking for.

Re: Poll: How many programmers don't know about bit-wise operations?

#75

Post by cognivore »

The original article by was on how compilers did optimizations using bitwise operations, which makes perfect sense. In day to day programming they can be useful, but all too often I run into code where they've obfuscated what's going on being clever with their operators, bitwise included. If the compiler can optimize it for us, write something clear and and obvious but not necessarily optimal. Code is for people.

Re: Poll: How many programmers don't know about bit-wise operations?

#76

Post by informatimago »

jared314 wrote: post #23

I have always wondered why I was taught binary as if they were arrays, but programming languages never allowed me to use bits like arrays. It's always masking and shifting uint16_t or int32_t, instead of what I really want, "result = bits[3] xor bits2[3]".

That's because you're using crude programming languages. Sophisticated programming languages let you use arrays of bits, as well as manipulating bits in integers.

    (let ((a (make-array '(4 2) :element-type 'bit
                         :initial-contents '((1 1) (1 0) (0 1) (0 0))))
          (b (make-array '(4 2) :element-type 'bit
                         :initial-contents '((1 0) (1 0) (1 0) (1 0)))))
      (list (list a 'xor b '--> (bit-xor a b))
            (list (aref a 0 1) 'xor (aref b 0 1) '--> (logxor (aref a 0 1) (aref b 0 1)))
            (list #b1100 'xor #b1010 '--> (logxor #b1100 #b1010))))
    --> ((#2A(#*11 #*10 #*01 #*00) xor #2A(#*10 #*10 #*10 #*10) --> #2A(#*01 #*00 #*11 #*10))
         (1 xor 0 --> 1)
         (12 xor 10 --> 6))

Re: Poll: How many programmers don't know about bit-wise operations?

#79

Post by anigbrowl »

saravk wrote: post #36
anigbrowl wrote: post #4

I like the elegance of bitwise operations and use them sometimes in signal processing applications to avoid a performance hit, though I'm no expert. But I avoid them in any high level code because a) the compiler is likely going to optimize that anyway and b) to be as human-readable as possible, the code should clearly describe the objective rather than exploit the underlying mechanism. In other words if I want to mu…

This is where macros (C) come in to play. Using macros (do all the bit shifting and masking inside) you can write very human readable code that is easy to maintain and while at the same time offers all the advantages of using bit-masks. The major advantage of bitwise operators for me is the memory savings that come with them. I used to write the route calculation algorithms for routers and every bit/byte save had an…

Great point and excellent context.

Re: Poll: How many programmers don't know about bit-wise operations?

#80

Post by fakeer »

PommeDeTerre wrote: post #72
fakeer wrote: post #65

Earlier quoted context omitted.

>> those people generally mean "C++" I've never worked on C++(as in on commercial project or in a C++ team) however I've always mentioned it on my resume as C/C++, because I've worked on C(Kernel wrt Android and a little bit more) but for C++ I've only built one academic project(very minor) during UG and also took (2nd yr) DS in C++. I just do not want to miss a good job offer which requires C++. Because in the inter…

No offense is meant, but I think you're doing yourself and potential employers a disservice by listing C++ on your resume when, based on your description, you have essentially no real-world experience with it. There is much, much more to writing solid, production-grade C++ code than could ever be learned during a minor academic project and a single undergraduate data structures course. This is especially true with th…

None taken.

You are right or you maybe right. When I joined my first job and started writing code from Day3(after initial HR/management hoopla doopla) I didn't have any commercial experience at all and I was up and going within 15 days. Must say it was a good team and now as I've experience and have some(or a little more than some) idea how things work, I believe I can pull it off.

Besides in the interviews I clearly mention the fact. It's not as if I've pasted some fictitious project/work. It's just there in C/C++. Along with Java and Python. That's it. And as I've already mentioned even when I mention C++ they test me for C only a little bit Java.

Back here, other than in startups and a few companies you are just tested for DS/Algo etc and not at all especially for a platform/technology. With the belief that the candidate will pick a language putting some effort which I believe, thought it may not be very fruitful for for a critical project where immediate expertise is required. In my last switch I was interviewed in C and worked on Java after that.

>>you have essentially no real-world experience

What do you called a real world experience? something that brought in rupees? Or sth that was used my thousands of people if not millions? Well, if that's your criteria then no I do not have real wold C++ experience.

But if you meant by sth that actually existed in real world and sth that I built from scratch and sth that was used by people - even a few, then I used my C++ text editor for over 6 months and some of my friends used it too, for some time :-)

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