Our February meeting had one presentation, by Travis, on parsing Roman Numerals. If you are not familiar with roman numerals, details can be found on Wikipedia 1. Luckily it was a simple problem, that kept everyone in the meeting involved.
The presenter, put together a couple versions of a parser, and later he compared the performance between them.
OS: Ubuntu 8.10 CPU: i7 920 @ 2.67GHz MEM: 3GB [yoann-c] runs: 0.008802 0.007679 0.007488 0.007645 0.007756 0.007639 0.007509 0.008596 0.007591 0.017954 average: 0.008866 s [travis-c-unrolled] runs: 0.013745 0.006565 0.006541 0.0063 0.00639 0.006344 0.00636 0.006961 0.006567 0.006396 average: 0.007217 s [travis-hs] runs: 0.178778 0.093547 0.092922 0.092819 0.092559 0.092501 0.092348 0.092178 0.092826 0.092133 average: 0.101261 s
It was obvious that the c versions were heavily optimized, travis-c-unrolled was essentially a case statement with every possible branch (3999), yoann-c was a rolled-up version.
The haskell version, provided below, performed the poorest. We did run it through the profiler to determine what the possible slow-downs were, but at quick glance there was nothing obvious. By that time it was getting late and we packed it in.
After the meeting we invited anyone to join in on a hackathon, sometime before ICFPC 2009. A date has yet to be decided, but we plan on working on a open source mail list manager, written in Haskell, called mhailist. If anyone is interested in signing up please contact firstname.lastname@example.org.
rnMeta :: String -> Int -> (Maybe Int, String) -> (Maybe Int, String) rnMeta _ _ t@(Nothing, _) = t rnMeta (c1:c5:c10:) mult (Just tot, xs) | lxs > 1 && x0 == c1 && x1 == c10 = (Just (tot + mult * 9), xs2) | lxs > 1 && x0 == c1 && x1 == c5 = (Just (tot + mult * 4), xs2) | lxs > 0 && x0 == c5 && nts1 < 4 = (Just (tot + mult * (5 + nts1)), xs1') | nts0 < 4 = (Just (tot + mult * nts0), xs0') | otherwise = (Nothing, xs) where lxs = length xs x0 = head xs xs1 = tail xs x1 = head xs1 xs2 = tail xs1 (ts0, xs0') = span (== c1) xs nts0 = length ts0 (ts1, xs1') = span (== c1) xs1 nts1 = length ts1 rnMeta (c1:) mult (Just tot, xs) | nts0 < 4 = (Just (tot + mult * nts0), xs0') | otherwise = (Nothing, xs) where (ts0, xs0') = span (== c1) xs nts0 = length ts0 rton :: String -> Maybe Int rton xs = case proc1 (proc2 (proc3 (proc4 (Just 0, xs)))) of (Just tot, ) -> Just tot _ -> Nothing where proc1 = rnMeta "IVX" 1 proc2 = rnMeta "XLC" 10 proc3 = rnMeta "CDM" 100 proc4 = rnMeta "M" 1000 main :: IO () main = interact (unlines . (map (getString . rton)) . lines) where getString :: Maybe Int -> String getString (Just tot) = show tot getString _ = "invalid Roman numeral"