in reply to Re^6: NaN output
in thread NaN output

I'll repeat it.

Oops ... was that for *my* benefit ?
You're not telling me anything (here) that I don't already know.
However, looking back at my posts, at no time did I state that explicitly ... though I did make a couple of attempts to make it implicitly apparent - eg a reference to "trick" and the acknowledgement that I wasn't contradicting anything you had said.

I did think it worthy of mention (but even that's probably debatable in hindsight) that in perl you can start with integers and operate on them in such a way that you derive a NaN - because you can't do that in (eg) C, afaik.

I also wondered whether that might have been something like the pathway that led Laurent_R to the view that you could get a NaN from integer overflow.
But it seems Laurent_R was alert to that aspect, anyway.

Cheers,
Rob

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Re^8: NaN output
by BrowserUk (Patriarch) on Mar 06, 2014 at 09:41 UTC
    You're not telling me anything (here) that I don't already know.

    And what was there in your post that you thought that I didn't already know?

    All I said was, you cannot get NaN from integer overflow. That was, is and always will be true.

    How Laurent_R's misunderstanding came about is irrelevant; that it should be corrected isn't.

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
      And what was there in your post that you thought that I didn't already know?

      Absolutely nothing (except see below my sig).
      You thought I was replying to you ? ... that I was trying to correct something you had said ? ... that I was trying to improve on something you had said ?
      You thought I was writing that post (at least in part) for your own edification ?
      After all, my post appeared directly beneath yours ... and it did start with a quote from your post.

      Well, it's "none of the above". I wasn't really replying to you, nor was I attempting to correct/improve your post. I was just making a divergent and trivial follow-on comment that was triggered partly by the (quoted) remark you had made, and partly by what Laurent_R had written.
      I thought you would pick up on that. (You *can* read minds, can't you ?)
      My apologies for that - my intent would have been much clearer if I had positioned my reply beneath Laurent_R's post and been way more explicit wrt what I was trying to say. There was really no need for me to reference your post at all - it's just that it was your remark that triggered the observation.

      Shit - all that for something I've written that probably wasn't of much interest to anyone other than me, anyway.
      Oh, well ... all I can do is try to do better next time.

      Cheers,
      Rob

      PS: Actually I wasn't sure whether you were aware that you could start with a couple of IV's and generate a NaN. It's pretty trivial, so it's of little consequence whether that had occurred to you or not. It seems a bit odd to me - as someone once said, "NaN is a purely floating point concept".
      I thought you *might* find that mildly interesting in some way.
      Yeah - I assume way too much :-)
[reply]
        you could start with a couple of IV's and generate a NaN.

        The problem (for me) is that there are no IVs involved in your construction.

        The basic compile-time constant: 2**1025 never results in the construction of any IVs.

        The interpreter constructs a compile-time constant from the expression and stores it as an NV:

        Perl> use Devel::Peek;;
Perl> $x = 2**1025;;
Perl> Dump( $x );;
SV = NV(0xb4598) at 0x3d73ee8
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  NV = 1.#INF

        [download]

        And then at runtime, one NV (value 1.#INF) is divided by another NV (also 1.#INF) and the results is an NV (value: -1.#IND):

        $y = $x / $x;;
Dump $y;;
SV = NV(0xb45a0) at 0x3d6c6a8
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  NV = -1.#IND

        [download]

        No IVs were ever involved because the textual integer expression from the source code never made into the byte-coded Perl.

        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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