As grinder points out, since the primes are being found in ascending order, it would make sense (and go really fast) to limit the for loop to just the hash keys that are the primes found so far.

But there's another issue in comparing the OP code with liverpole's revision: the outputs are different.

If I add  warn "$x $y $colr\n"; after the call to "createText" in each version, then run each of them with a "maximum number" value of 6000 and redirect stderr to a separate file for each version, both scripts produce 6000 lines of output, and the x and y values match perfectly line-by-line in the two files. But the color values are quite different, starting at the first line.

I wanted to check that, because it seemed to me that liverpole's faster version was not as "dark" as the OP version, and sure enough, the optimized/faster script produces 1694 white pixels, 4306 black ones, in contrast to the OP code, which produces only 783 white, and 5217 black. The two versions disagree on color in 911 of the 6000 outputs. (That is, all the disagreements involve points where the OP said "black" and liverpole said "white".)

It probably involves the strange use of  $prime_[1] in the OP (where it probably should have been "$p" instead of "1", but it's hard to be sure what the intent was there). update: I had assumed (probably wrongly) that the OP code was drawing primes in black, but my tabulation showed 783 white dots drawn for a max value of 6000, and that turns out to be the correct number of primes in that range. Sorry liverpole, it looks like there's a problem in your math somewhere.

In reply to Re^2: ulam's spiral too slow by graff
in thread ulam's spiral too slow by orange

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.