Hi Don (and cafe), Given the example you just posted, is there a simple way to generate the de-sugared haskell / core / STG / labelled-assembly versions of a piece of haskell code? For instance, how did you generate the content below? I guess this is the core language version? I'm a C/C++ coder and looking for the equivalent of "Show Disassembly". Cheers, Sam -----Original Message----- From: haskell-cafe-bounces@haskell.org on behalf of Don Stewart Sent: Mon 18/05/2009 14:50 To: Kenneth Hoste Cc: Haskell Cafe mailing list Subject: Re: [Haskell-cafe] fast Eucl. dist. - Haskell vs C kenneth.hoste:
Hello,
For a while now, I've been trying to come up with a fast Haskell-only function which implements Euclidean distance in n-dimensional space.
So far, I've been disappointed by the performance of my best effort in Haskell, compared to C. I'm hoping some of the Haskell experts and/or performance gurus on this list can help me out on resolving this, and also maybe shed some light on some strange (imho) things I've run into.
My current best try uses the uvector package, has two 'vectors' of type (UArr Double) as input, and relies on the sumU and zipWithU functions which use streaming to compute the result:
dist_fast :: UArr Double -> UArr Double -> Double dist_fast p1 p2 = sumDs `seq` sqrt sumDs where sumDs = sumU ds ds = zipWithU euclidean p1 p2 euclidean x y = d*d where d = x-y
The problem in your uvector code is the use of lists, rather than uvector generators. Replace [1..n] with enumFromTo: import Control.Monad import System.Environment import System.IO import Data.Array.Vector dist :: UArr Double -> UArr Double -> Double dist p1 p2 = sumU (zipWithU euclidean p1 p2) where euclidean x y = d*d where d = x-y main = do [dim] <- map read `fmap` getArgs print $ dist (enumFromToFracU 1.0 dim) (enumFromToFracU 1.0 dim) Now the entire thiing will fuse to a loop. $s$wfold_s1RR :: Double# -> Double# -> Double# -> Double# $s$wfold_s1RR = \ (sc_s1RH :: Double#) (sc1_s1RI :: Double#) (sc2_s1RJ :: Double#) -> case >## sc1_s1RI a5_s1QR of wild4_a1tn { False -> case >## sc_s1RH a5_s1QR of wild5_X1vx { False -> let { x1_a1Jg [ALWAYS Just L] :: Double# x1_a1Jg = -## sc1_s1RI sc_s1RH } in $s$wfold_s1RR (+## sc_s1RH 1.0) (+## sc1_s1RI 1.0) (+## sc2_s1RJ (*## x1_a1Jg x1_a1Jg)); True -> sc2_s1RJ }; True -> sc2_s1RJ }; } in case $s$wfold_s1RR 1.0 1.0 0.0 of ww_s1QH { __DEFAULT -> a19 (D# ww_s1QH) and this assembly: $ ghc -O2 -fvia-C -optc-O3 s1T9_info: movsd 5(%rbx), %xmm7 ucomisd %xmm7, %xmm6 ja .L15 ucomisd %xmm7, %xmm5 jbe .L18 .L14: .L15: movsd (%rbp), %xmm5 leaq 8(%rbp), %rbp jmp *(%rbp) .L18: movapd %xmm6, %xmm7 subsd %xmm5, %xmm7 mulsd %xmm7, %xmm7 addsd (%rbp), %xmm7 movsd %xmm7, (%rbp) movsd .LC0(%rip), %xmm7 addsd %xmm7, %xmm5 addsd %xmm7, %xmm6 jmp s1T9_info Which I'd wager will match the C, which has to allocate the two arrays (GHC essentially decides it doesn't need the arrays any more. -- Don _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe