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    CompSci Weekend SuperThread (January 05, 2018) Computer Science

    January 05, 2018

    CompSci Weekend SuperThread (January 05, 2018) Computer Science

    CompSci Weekend SuperThread (January 05, 2018)

    Posted: 04 Jan 2018 05:05 PM PST

    /r/compsci strives to be the best online community for computer scientists. We moderate posts to keep things on topic.

    This Weekend SuperThread provides a discussion area for posts that might be off-topic normally. Anything Goes: post your questions, ideas, requests for help, musings, or whatever comes to mind as comments in this thread.

    Pointers

    • If you're looking to answer questions, sort by new comments.
    • If you're looking for answers, sort by top comment.
    • Upvote a question you've answered for visibility.
    • Downvoting is discouraged. Save it for discourteous content only.

    Caveats

    • It's not truly "Anything Goes". Please follow Reddiquette and use common sense.
    • Homework help questions are discouraged.
    submitted by /u/AutoModerator
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    Can someone explain to me how SWAR works like I am an absolute idiot? (*SPOILER ALERT: I REALLY AM AN IDIOT*)

    Posted: 04 Jan 2018 12:58 PM PST

    Vector processing within a register. Simple as that right? For some reason I cannot fathom how it really does work in practice I have seen pictures of 64 bit processors being split into different parts and having them work over different sizes of data but I cannot just get it in my head. It is frustrating....

    Will somebody be kind enough to help out the Karl Pilkington of computer science to prepare for this exam I have coming?

    submitted by /u/ElliotSpelledBackwar
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    What is the name of this coding scheme for very large integers?

    Posted: 04 Jan 2018 04:36 PM PST

    I've got a coding scheme in mind for very large, variable-length integers, and I am wondering if I am the inventor, or if it already exists and has a name and even an implementation.

    Here's the format:

    [length][data]

    Length is one byte long, and cannot be 0. It specifies the length of data.

    [0][length_2][length][data]

    If your number is too large for the above format, set the first byte equal to 0. This denotes one additional level of indirection. The first byte after the 0, labeled length_2, is the length of the length section. The length of the data section is then the value of the length section read as an unsigned integer.

    [0][0][length_3][length_2][length][data]

    If your number is too large for even that format, set the first two bytes equal to 0, which denotes two additional levels of indirection. Then the value of the one-byte length_3 section gives you the length of length_2, whose value gives the length of length, whose value gives the length of data.

    [0]n-1[length_n]...[length][data]

    This can be carried on indefinitely to represent arbitrarily large numbers.

    Note: The number 0 cannot simply be represented as 0x00 denoting a 0-length data section, since this would be interpreted as a layer of indirection; it actually has to be represented as 0x01 0x00 denoting a 1-length data section with value 0.

    So, what's this format called? Or do I get to name it? If I get to name it, I'm calling it "VLI format" for "Very Large Integer".

    submitted by /u/Negatratoron
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    Honest question about TAOCP/Donald Knuth

    Posted: 04 Jan 2018 04:03 PM PST

    So, we know that volume 4 is well on its way to completion, and volume 5 is slated for 2025. I recently got the MMIX supplement, volume 1, and 4A, and am really enjoying reading it so far. Alongside idolizing Knuth as a computer scientist and enjoying his writing, a lingering thought has been at the back of my head. He is 79 right now and will be at least 87 with the release of volume 5. What will happen in the event he unexpectedly dies? Will the remaining volumes be left incomplete, or will some other person be tasked with completing it? Is there anyone even capable of matching his knowledge to complete the book?

    submitted by /u/BushDidN0thingWr0ng
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    SPMD runs in lockstep? MPMD???

    Posted: 04 Jan 2018 03:32 PM PST

    I have not seen a Single Program Multiple Programs processor lock stepping in front of Buckingham Palace (though it is a funny thought), can anyone explain to me what is it meant by that.

    In my lecture notes, it is explained as "SIMD runs the same program on multiple processors in lockstep, so every processor is executing the same instruction". It might be clear to someone who knows how it works but clearly not to me.

    Then I have the Multiple Programs, Multiple Data designs which in my notes is just explained as "A Machine not running SPMD, so each processor running potentially different programs e.g. master-slave models or systolic pipelines." I have no idea what the lecturer is on about and googling it makes it even more confusing.

    To be completely frank, my lecturer made his notes in a way that they are perfectly clear to himself and anybody who is already familiar with whatever he is talking about which is not particularly good for me.

    submitted by /u/ElliotSpelledBackwar
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    Biggest Testing Failures of 2017 [X-POST]

    Posted: 04 Jan 2018 07:52 AM PST
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