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    <p>Pass 2, about 30% better (on my machine) than my previous. The main saving came from unrolling the inner loop to amortize the overhead.</p> <p>Also included (commented out) is an aborted attempt to save time by exiting early (&amp; set the pixel black) when you are stuck in the central cardioid. It works, but it's slower no matter how I jiggered it.</p> <p>I've got to run, but I'll leave a parting suggestion. There may be some optimization possible by run-length encoding the results (so instead of saving a bunch of bit-twiddled chars you'd save a list (number of white dots, number of black dots, number of white dots, etc.)). This would:</p> <ol> <li>Reduce the storage/GC overhead </li> <li>Allow some optimizations on the output generation (when the numbers were >> 8)</li> <li>Permit some orbit detection.</li> </ol> <p>No idea if it could be coded tight enough to fly, but that is where I would try next if I had more time.</p> <pre><code>-- The Computer Language Shootout -- http://shootout.alioth.debian.org/ -- contributed by Mike Pall -- with optimizations by Markus J. Q. (MarkusQ) Roberts local width = tonumber(arg and arg[1]) or 100 local height, wscale = width, 2/width local m, limit2 = 50, 4.0 local write, char = io.write, string.char local h2 = math.floor(height/2) local hm = height - h2*2 local top_half = {} for y=0,h2+hm do local Ci = 2*y / height - 1 local line = {""} for xb=0,width-1,8 do local bits = 0 local xbb = xb+7 for x=xb,xbb &lt; width and xbb or width-1 do bits = bits + bits local Zr, Zi, Zrq, Ziq = 0.0, 0.0, 0.0, 0.0 local Cr = x * wscale - 1.5 local Zri = Zr*Zi for i=1,m/5 do Zr = Zrq - Ziq + Cr Zi = Zri + Zri + Ci Zri = Zr*Zi Zr = Zr*Zr - Zi*Zi + Cr Zi = 2*Zri + Ci Zri = Zr*Zi Zr = Zr*Zr - Zi*Zi + Cr Zi = 2*Zri + Ci Zri = Zr*Zi Zr = Zr*Zr - Zi*Zi + Cr Zi = 2*Zri + Ci Zri = Zr*Zi Zr = Zr*Zr - Zi*Zi + Cr Zi = 2*Zri + Ci Zri = Zr*Zi Zrq = Zr*Zr Ziq = Zi*Zi Zri = Zr*Zi if Zrq + Ziq &gt; limit2 then bits = bits + 1 break end -- if i == 1 then -- local ar,ai = 1-4*Zr,-4*Zi -- local a_r = math.sqrt(ar*ar+ai*ai) -- local k = math.sqrt(2)/2 -- local br,bi2 = math.sqrt(a_r+ar)*k,(a_r-ar)/2 -- if (br+1)*(br+1) + bi2 &lt; 1 then -- break -- end -- end end end for x=width,xbb do bits = bits + bits + 1 end table.insert(line,char(255-bits)) end line = table.concat(line) table.insert(top_half,line) end write("P4\n", width, " ", height, "\n") for y=1,h2+hm do write(top_half[y]) end for y=h2,1,-1 do write(top_half[y]) end </code></pre>
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    1. POLua Challenge: Can you improve the mandelbrot implementation’s performance?
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    1. COCongratulations! It would've been nice to have more contestants, but either way great work!
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    2. COI agree. It would have been fun to have more time to spend on it too. Thanks for posting a great question.
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