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April 2009
f(x) = ((((x * c1) & c2) * c3) & c4) % c5, where
c1 = (2792-1)/(233-1);
c2 = (2816-1)/(234-1);
c3 = 1+234+23*34+24*34+28*34;
c4 = (21088-1)/(234-1)
c5 = 233-1;
We encoded a linear erasure code using O(1) operations, thanks to Eli Biham who gave us a simpler solution. A nice discussion on this issue can be found at http://www.brand.site.co.il/riddles/200902q.html (link resides outside of ibm.com) and the links from it.
If you have any problems you think we might enjoy, please send them in. All replies should be sent to: ponder@il.ibm.com