These sound reasonable, do we have any (micro)benchmarks to validate
#9638: Speed up Data.Char.isDigit -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.9 Component: | Keywords: libraries/base | Architecture: Unknown/Multiple Resolution: | Difficulty: Easy (less than 1 Operating System: | hour) Unknown/Multiple | Blocked By: Type of failure: Runtime | Related Tickets: performance bug | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:3 carter]: that there's a meaningful improvement in performance to pay down the increased complexity of the implementation? Yes. I tested evaluating `nf (map isDigit) testcase` with the following test cases: {{{#!hs toosmall = replicate 700 '-' toobig = replicate 700 'a' justright = replicate 700 '7' arb = "12asaa489oneuhl98'c43rub93d'i'i98car278urnatehodth98228hteou84348hcae84--- - - 424 42 hteohu 2 4hto24hth ehua942dp.dghckbaa---; 48923" arbitrary = arb ++ arb ++ reverse arb ++ reverse arb }}} As expected, the fancy code seemed to be very slightly worse for `toosmall`, certainly not worse enough to really get a proper measurement (it's only one extra addition). The rest did better with the fancy code; the difference was consistently biggest for `arbitrary`. Obviously we're not talking huge changes, but I think this function and similar ones get a good bit of use, so it's probably worth bothering. {{{ benchmarking toosmall/old time 12.31 μs (12.27 μs .. 12.36 μs) 1.000 R² (0.999 R² .. 1.000 R²) mean 12.37 μs (12.34 μs .. 12.40 μs) std dev 100.2 ns (69.41 ns .. 138.7 ns) benchmarking toosmall/new time 12.42 μs (12.41 μs .. 12.43 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 12.43 μs (12.42 μs .. 12.44 μs) std dev 36.07 ns (24.75 ns .. 59.63 ns) benchmarking toobig/old time 13.05 μs (13.04 μs .. 13.06 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 13.05 μs (13.04 μs .. 13.06 μs) std dev 26.99 ns (19.95 ns .. 43.44 ns) benchmarking toobig/new time 12.43 μs (12.42 μs .. 12.45 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 12.45 μs (12.44 μs .. 12.48 μs) std dev 65.84 ns (32.99 ns .. 129.0 ns) benchmarking justright/old time 13.07 μs (13.06 μs .. 13.08 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 13.08 μs (13.06 μs .. 13.09 μs) std dev 42.63 ns (30.33 ns .. 56.90 ns) benchmarking justright/new time 12.41 μs (12.40 μs .. 12.42 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 12.41 μs (12.41 μs .. 12.42 μs) std dev 25.29 ns (21.00 ns .. 31.20 ns) benchmarking arbitrary/old time 11.69 μs (11.68 μs .. 11.71 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 11.69 μs (11.68 μs .. 11.71 μs) std dev 50.41 ns (21.45 ns .. 85.71 ns) benchmarking arbitrary/new time 10.65 μs (10.64 μs .. 10.66 μs) 1.000 R² (1.000 R² .. 1.000 R²) mean 10.65 μs (10.64 μs .. 10.66 μs) std dev 21.31 ns (14.90 ns .. 36.62 ns) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9638#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler