http://snippets.dzone.com/posts Tue, 07 Oct 2008 10:24:15 GMT DZone Snippets: knuth code http://snippets.dzone.com/posts/show/5181 In Donald Knuth's TAoCP Pre-Fascicle 1a: Bitwise Tricks and Techniques, he shows a patchwork quilt defined by f(x, y) = ((x ^ y) & ((y - 350) >> 3)) ** 2, designed by D. Sleator in 1976. I wanted to recreate this quilt myself using Ruby. The following program generates a PNG file of the "quilt." <br /> <br /><code> <br />require 'rubygems' <br />require 'png' <br /> <br />def f(x, y) <br /> ( (x ^ y) & ((y - 350) >> 3) ) ** 2 <br />end <br /> <br />canvas = PNG::Canvas.new(500, 500) <br /> <br />0.upto(499) do |y| <br /> 0.upto(499) do |x| <br /> canvas[x, 499 - y] = ((f(x, y) >> 12) & 1) == 1 ? PNG::Color::Black : PNG::Color::White <br /> end <br />end <br /> <br />png = PNG.new(canvas) <br />png.save 'pattern.png' <br /></code> Wed, 27 Feb 2008 10:17:32 GMT http://snippets.dzone.com/posts/show/5181 peter (Peter Cooperx)