On Dec 3, 2007 9:10 PM, Don Stewart <[EMAIL PROTECTED]> wrote: > > Is there anything in any of the interfaces to Integer that will allow > > me to quickly find the highest bit set in an Integer? > Well, you could use testBit, which is pretty efficient,
But testBit tests only one bit at a time. To prove that i is the highest bit of n I need to prove that all higher bits are set to zero, and I can't do that with testBit. The obvious thing is "shiftR n i == 0" but I'm worried that that entails the wasteful operation of shifting all of the bits above bit i. Internally the implementation of Integer must know a good upper bound on where the highest bit is. Maybe I need to delve into GHC.Prim. -- Dan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
