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POquick/fast integer multiplication in ruby?
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copied!<p>I am trying to make a quick/efficient Mandelbrot implementation in Ruby. A long long time ago, one way to speed it up was using fixed point integers instead of floats.</p> <p>So i made the following benchmark, comparing float and integer raising to a square, using multiplication or square ** operand.</p> <pre><code>require 'benchmark' Benchmark.bmbm(10) do |x| x.report("float-multip") do for z in 0..100000 zf = z.to_f y = zf*zf end end x.report("float-square") do for z in 0..100000 zf = z.to_f y = zf**2 end end x.report("int-multip") do zo = 0 for zi in 0..100000 y2 = zo*zo zo += 1 end end x.report("int-multip") do for zi in 0..100000 y2 = zi**2 end end end </code></pre> <p>and this generates the following output:</p> <pre><code>Rehearsal ------------------------------------------------ float-multip 0.125000 0.000000 0.125000 ( 0.125000) float-square 0.125000 0.000000 0.125000 ( 0.125000) int-multip 0.250000 0.000000 0.250000 ( 0.250000) int-multip 0.282000 0.000000 0.282000 ( 0.282000) --------------------------------------- total: 0.782000sec user system total real float-multip 0.110000 0.000000 0.110000 ( 0.110000) float-square 0.125000 0.000000 0.125000 ( 0.125000) int-multip 0.219000 0.016000 0.235000 ( 0.235000) int-multip 0.265000 0.015000 0.280000 ( 0.282000) </code></pre> <p>which clearly shows the the Fixnum multiplication is almost twice as slow as floating point.</p> <p>I have two questions:</p> <ul> <li>Can anyone explain this? A reason I can imagine is that Fixnum multiplication is slower because of the internal checking whether or not it needs to be converted to a Bignum.</li> <li>secondly is there than a quick integer multiplication for ruby?</li> </ul>

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