On Dec 21, 2007 3:00 PM, Justin Bailey
It really did help. I started with an implementation that used Ints, and this sped the program up by at least 2x. I think that's because of the bit-manipulation I'm doing. For example, Data.Bits defines the bitwise and operation on Ints as:
(I# x#) .&. (I# y#) = I# (word2Int# (int2Word# x# `and#` int2Word# y#))
Which you can see has 3 conversions in it. The I# deconstruction/construction is also suspicious to me, but I don't know if there are performance costs there or not. Regardless, using Word# directly lets me write (assuming w1# and w2# are already words):
w1# `and#` w2#
Maybe better rewrite rules in the Data.Bits library would eliminate unnecessary conversions and this wouldn't be necessary
Wouldn't it be sufficient to use Data.Word and rely on GHC unboxing capabilities? Compiling import Data.Bits import Data.Word main = do a <- getLine b <- getLine print (read a .&. read b :: Word) with GHC 6.6.1 gives me (case GHC.Read.read @ GHC.Word.Word GHC.Word.$f40 a_afE of wild1_a1tT { GHC.Word.W# x#_a1tV -> case GHC.Read.read @ GHC.Word.Word GHC.Word.$f40 a87_a1ub of wild11_a1tW { GHC.Word.W# y#_a1tY -> GHC.Word.$w$dmshow1 (GHC.Prim.and# x#_a1tV y#_a1tY) } }) which of course does the right thing. Cheers, -- Felipe.