Hi, Am Sonntag, den 18.09.2011, 18:46 -0400 schrieb Edward Kmett:
You can use a smaller DeBruijn multiplication table to handle 32 bits, but the one that I gave puts the answer in the most significant 6 bits of a 64 bit word, so if you use it with a 32 bit word, they'll be setting bits you don't have and all answers will be 0.
I’m not sure how to cleanly select the right implementation inside Data.IntMap. Also, we have architectures with 31 bit words (s390, at least). If anything, then the functions ought to move into the Bits type class and into GHC.Word. There it makes also more sense to select architecture-specific implementations, e.g. the primitive operation on x86.
Also, if you don't care about the particular order in which you visit the bits you could store the bits in a different order in the Word(64) than you would if you just set them directly by preshuffling them.
The order is unfortunately relevant, and I am not sure I have a use for an arbitrarily ordered fold. Greetings, Joachim -- Joachim "nomeata" Breitner mail@joachim-breitner.de | nomeata@debian.org | GPG: 0x4743206C xmpp: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/