in reply to Sheer idle curiousity . . .

What does your intuition tell you this code does?

d=>sub{
    $wait = 0 unless abs($wait);
    $wait = -34;
},

[download]

In particular, abs returns the absolute value. The absolute value of -34 is 34, which is "true". Since your condition is never false, you never fall through to the action of the "unless" clause.


Dave

Replies are listed 'Best First'.
Re^2: Sheer idle curiousity . . .
by TheMonkWithoutVows (Novice) on Oct 23, 2013 at 22:16 UTC

    My intuition tells me it's been a long day and typos are creeping in :-)

    The last test should have read:

       d=>sub{
                $wait = 0 unless ($wait == abs($wait));
                $wait = -34;
                },

    [download]
    I thought the results had shot up on my home pc. 
          Rate    d    c    b    a
d 3468819/s   --  -8% -10% -13%
c 3780923/s   9%   --  -1%  -5%
b 3834916/s  11%   1%   --  -4%
a 3997317/s  15%   6%   4%   --


and 

       Rate    d    c    b    a
d 3246175/s   --  -8% -15% -17%
c 3526456/s   9%   --  -7%  -9%
b 3799184/s  17%   8%   --  -2%
a 3890565/s  20%  10%   2%   --

    [download]

    It's still the outright winner - so the questions still stand.

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Re^2: Sheer idle curiousity . . .
by boftx (Deacon) on Oct 23, 2013 at 22:08 UTC

    Besides what David just said, it seems to me that the operation of simply setting a sign bit and then testing for 0 would inherently faster than any of the other comparisons if the resulting code is optimized. I know that would be the case if I were coding that in assembly.

    The answer to the question "Can we do this?" is always an emphatic "Yes!" Just give me enough time and money.
[reply]
      if the resulting code is optimized.

      Its not. It just results in less opcodes.

      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]

        That was what I was driving at. I know that I could code that in 2 or 3 opcodes using nothing but bitwise operations if hand-coding. If the zero flag were set with a simple load then I could code it in a single opcode (excluding the jump codes.)

        The answer to the question "Can we do this?" is always an emphatic "Yes!" Just give me enough time and money.
[reply]

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