diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,3 @@
+## 0.1
+
+* Initial release.
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 Bodigrim
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,16 @@
+# tasty-bench-fit
+
+Benchmark a given function for variable input sizes and find out its time complexity.
+
+```haskell
+> fit $ mkFitConfig (\x -> sum [1..x]) (10, 10000)
+1.2153e-8 * x
+> fit $ mkFitConfig (\x -> Data.List.nub [1..x]) (10, 10000)
+2.8369e-9 * x ^ 2
+> fit $ mkFitConfig (\x -> Data.List.sort $ take (fromIntegral x) $ iterate (\n -> n * 6364136223846793005 + 1) (1 :: Int)) (10, 100000)
+5.2990e-8 * x * log x
+```
+
+One can usually get reliable results for functions, which do not allocate much: like in-place vector sort or fused list operations like `sum [1..x]`.
+
+Unfortunately, fitting functions, which allocate a lot, is likely to be disappointing: GC kicks in irregularly depending on nursery and heap sizes and often skews observations beyond any recognition. Consider running such measurements with `-O0` or in `ghci` prompt. This is how the usage example above was generated. Without optimizations your program allocates much more and triggers GC regularly, somewhat evening out its effect.
diff --git a/src/Test/Tasty/Bench/Fit.hs b/src/Test/Tasty/Bench/Fit.hs
new file mode 100644
--- /dev/null
+++ b/src/Test/Tasty/Bench/Fit.hs
@@ -0,0 +1,197 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE NumDecimals #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+-- | Guess complexity of the function.
+module Test.Tasty.Bench.Fit (
+  -- * Fit benchmarks
+  fit,
+  fits,
+  mkFitConfig,
+  FitConfig (..),
+
+  -- * Complexity
+  Complexity (..),
+  Measurement (..),
+  guessComplexity,
+  evalComplexity,
+
+  -- * Predicates
+  isConstant,
+  isLogarithmic,
+  isLinear,
+  isLinearithmic,
+  isQuadratic,
+  isCubic,
+) where
+
+import Control.DeepSeq (NFData)
+import Data.List (maximumBy)
+import Data.List.NonEmpty (NonEmpty (..))
+import qualified Data.List.NonEmpty as NE
+import Data.Map (Map)
+import qualified Data.Map as M
+import Data.Ord (comparing)
+import System.IO.Unsafe (unsafeInterleaveIO)
+import Test.Tasty (Timeout, mkTimeout)
+import Test.Tasty.Bench (Benchmarkable, RelStDev (..), measureCpuTimeAndStDev, nf)
+import Test.Tasty.Bench.Fit.Complexity (
+  Complexity (..),
+  Measurement (..),
+  evalComplexity,
+  guessComplexity,
+  isConstant,
+  isCubic,
+  isLinear,
+  isLinearithmic,
+  isLogarithmic,
+  isQuadratic,
+ )
+
+#ifdef DEBUG
+import Debug.Trace
+#endif
+
+-- | Configuration for 'fit'.
+data FitConfig = FitConfig
+  { fitBench :: Word -> Benchmarkable
+  -- ^ Which function to measure? Typically 'nf' @f@.
+  , fitLow :: Word
+  -- ^ The smallest size of the input.
+  -- It should be as small as possible, but big enough for the main asymptotic
+  -- term to dwarf constant overhead and other terms.
+  , fitHigh :: Word
+  -- ^ The largest size of the input.
+  -- As large as practically possible, at least 100x larger than
+  -- the smallest size.
+  , fitTimeout :: Timeout
+  -- ^ Timeout of individual measurements.
+  , fitRelStDev :: RelStDev
+  -- ^ Target relative standard deviation of individual measurements.
+  , fitOracle :: Map Word Measurement -> Complexity
+  -- ^ An oracle to determine complexity from measurements.
+  -- Typically 'guessComplexity'.
+  }
+
+-- | Generate a default 'fit' configuration.
+mkFitConfig
+  :: (NFData a)
+  => (Word -> a)
+  -- ^ Raw function to measure, without 'nf'.
+  -> (Word, Word)
+  -- ^ The smallest and the largest sizes of the input.
+  -> FitConfig
+mkFitConfig f (low, high) =
+  FitConfig
+    { fitBench = nf f
+    , fitLow = low
+    , fitHigh = high
+    , fitTimeout = mkTimeout 1e8
+    , fitRelStDev = RelStDev 0.02
+    , fitOracle = guessComplexity
+    }
+
+-- | Determine time complexity of the function:
+--
+-- >>> fit $ mkFitConfig (\x -> sum [1..x]) (10, 10000)
+-- 1.2153e-8 * x
+-- >>> fit $ mkFitConfig (\x -> Data.List.nub [1..x]) (10, 10000)
+-- 2.8369e-9 * x ^ 2
+-- >>> fit $ mkFitConfig (\x -> Data.List.sort $ take (fromIntegral x) $ iterate (\n -> n * 6364136223846793005 + 1) (1 :: Int)) (10, 100000)
+-- 5.2990e-8 * x * log x
+--
+-- One can usually get reliable results for functions, which do not
+-- allocate much: like in-place vector sort or fused list operations like
+-- 'sum' @[1..x]@.
+--
+-- Unfortunately, fitting functions, which allocate a lot,
+-- is likely to be disappointing: GC kicks in irregularly depending on nursery
+-- and heap sizes and often skews observations beyond any recognition.
+-- Consider running such measurements with @-O0@ or in @ghci@ prompt. This is how
+-- the usage example above was generated. Without optimizations your program
+-- allocates much more and triggers GC regularly, somewhat evening out its effect.
+fit :: FitConfig -> IO Complexity
+fit cnf = converge <$> fits cnf
+
+converge :: NonEmpty Complexity -> Complexity
+converge xs = case zs of
+  [] -> NE.last xs
+  (_, _, z) : _ -> z
+  where
+    ys = NE.toList xs
+    zs =
+      dropWhile (\(x, y, z) -> p x z || p y z) $
+        zip3 ys (tail ys) (drop 2 ys)
+    p
+      Complexity {cmplVarPower = varPow, cmplLogPower = logPow, cmplMultiplier = mult}
+      Complexity {cmplVarPower = varPow', cmplLogPower = logPow', cmplMultiplier = mult'} =
+        abs (varPow - varPow') > 0.001
+          || logPow /= logPow'
+          || abs ((mult - mult') / mult) > 0.01
+
+-- | Same as 'fit', but interactively emits a list of complexities,
+-- gradually converging to the final result.
+--
+-- If 'fit' takes too long, you might wish to implement your own criterion
+-- of convergence atop of 'fits' directly.
+fits :: FitConfig -> IO (NonEmpty Complexity)
+fits FitConfig {..} = unsafeInterleaveIO $ do
+  lowTime <- measure fitLow
+  highTime <- measure fitHigh
+  let mp = M.fromList [(fitLow, lowTime), (fitHigh, highTime)]
+      cmpl = fitOracle mp
+  cmpl `seq` (cmpl :|) <$> go mp
+  where
+    measure :: Word -> IO Measurement
+    measure =
+      fmap (uncurry Measurement)
+        . measureCpuTimeAndStDev fitTimeout fitRelStDev
+        . fitBench
+
+    processGap
+      :: forall t
+       . (Ord t)
+      => [(Word, t)]
+      -> Map Word Measurement
+      -> IO (Map Word Measurement)
+    processGap gaps mp
+      | M.null gaps' = pure mp
+      | otherwise = (\m -> M.insert maxGap m mp) <$> measure maxGap
+      where
+        gaps' = M.fromList gaps `M.difference` mp
+        maxGap = fst $ maximumBy (comparing snd) $ M.toList gaps'
+
+    go :: Map Word Measurement -> IO [Complexity]
+    go mp = unsafeInterleaveIO $ do
+      let xys = M.toAscList $ fmap measTime mp
+          paired = zip xys (drop 1 xys)
+
+          arithGaps :: [(Word, Double)]
+          arithGaps =
+            map
+              (\((x, tx), (y, ty)) -> (round ((d x + d y) / 2), ty - tx))
+              paired
+
+          geomGaps :: [(Word, Double)]
+          geomGaps =
+            map
+              (\((x, tx), (y, ty)) -> (round (sqrt (d x * d y)), ty / tx))
+              paired
+
+      mp' <- processGap arithGaps mp
+      mp'' <- processGap geomGaps mp'
+      traceShowM' (M.keys mp'')
+      let cmpl = fitOracle mp''
+      traceShowM' cmpl
+      (cmpl :) <$> (if mp == mp'' then pure [] else go mp'')
+
+d :: Word -> Double
+d = fromIntegral
+
+traceShowM' :: (Applicative m, Show a) => a -> m ()
+#ifdef DEBUG
+traceShowM' = traceShowM
+#else
+traceShowM' = const (pure ())
+#endif
diff --git a/src/Test/Tasty/Bench/Fit/Complexity.hs b/src/Test/Tasty/Bench/Fit/Complexity.hs
new file mode 100644
--- /dev/null
+++ b/src/Test/Tasty/Bench/Fit/Complexity.hs
@@ -0,0 +1,283 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE PostfixOperators #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+
+-- | Guess complexity from data.
+module Test.Tasty.Bench.Fit.Complexity (
+  Complexity (..),
+  Measurement (..),
+  guessComplexity,
+  evalComplexity,
+
+  -- * Predicates
+  isConstant,
+  isLogarithmic,
+  isLinear,
+  isLinearithmic,
+  isQuadratic,
+  isCubic,
+) where
+
+import Control.DeepSeq (NFData)
+import Data.List (intercalate, minimumBy)
+import Data.List.Infinite (Infinite (..), (...))
+import qualified Data.List.NonEmpty as NE
+import Data.Map (Map)
+import qualified Data.Map as M
+import Data.Ord (comparing)
+import GHC.Generics (Generic)
+import Math.Regression.Simple (
+  Fit (..),
+  V2 (..),
+  levenbergMarquardt1WithYerrors,
+  levenbergMarquardt2WithYerrors,
+  linear,
+ )
+import Text.Printf (printf)
+import Prelude hiding (log)
+import qualified Prelude as P
+
+#ifdef DEBUG
+import Debug.Trace
+#endif
+
+log :: Word -> Double
+log x = if x >= 1 then P.log (d x) else 0
+
+-- | 'Complexity' @a@ @b@ @k@ represents a time complexity
+-- \( k \, x^a \log^b x \), where \( x \) is problem's size.
+data Complexity = Complexity
+  { cmplVarPower :: !Double
+  , cmplLogPower :: !Word
+  , cmplMultiplier :: !Double
+  }
+  deriving (Eq, Ord, Generic)
+
+instance NFData Complexity
+
+-- | Is the complexity \( f(x) = k \)?
+isConstant :: Complexity -> Bool
+isConstant = \case
+  Complexity {cmplVarPower = 0, cmplLogPower = 0} -> True
+  _ -> False
+
+-- | Is the complexity \( f(x) = k \log x \)?
+isLogarithmic :: Complexity -> Bool
+isLogarithmic = \case
+  Complexity {cmplVarPower = 0, cmplLogPower = 1} -> True
+  _ -> False
+
+-- | Is the complexity \( f(x) = k \, x \)?
+isLinear :: Complexity -> Bool
+isLinear = \case
+  Complexity {cmplVarPower = 1, cmplLogPower = 0} -> True
+  _ -> False
+
+-- | Is the complexity \( f(x) = k \, x \log x \)?
+isLinearithmic :: Complexity -> Bool
+isLinearithmic = \case
+  Complexity {cmplVarPower = 1, cmplLogPower = 1} -> True
+  _ -> False
+
+-- | Is the complexity \( f(x) = k \, x^2 \)?
+isQuadratic :: Complexity -> Bool
+isQuadratic = \case
+  Complexity {cmplVarPower = 2, cmplLogPower = 0} -> True
+  _ -> False
+
+-- | Is the complexity \( f(x) = k \, x^3 \)?
+isCubic :: Complexity -> Bool
+isCubic = \case
+  Complexity {cmplVarPower = 3, cmplLogPower = 0} -> True
+  _ -> False
+
+instance Show Complexity where
+  show Complexity {..} =
+    intercalate " * " $
+      filter
+        (not . null)
+        [ case cmplMultiplier of
+            1 -> ""
+            _ -> printf "%.2g" cmplMultiplier
+        , case cmplVarPower of
+            0 -> ""
+            1 -> "x"
+            _ -> "x ^ " <> round3 cmplVarPower
+        , case cmplLogPower of
+            0 -> ""
+            1 -> "log x"
+            _ -> "(log x) ^ " <> show cmplLogPower
+        ]
+    where
+      round3 :: Double -> String
+      round3 x = if x == d x' then show x' else printf "%.3f" x
+        where
+          x' :: Word
+          x' = round x
+
+-- | Evaluate time complexity for a given size of the problem.
+evalComplexity :: Complexity -> Word -> Double
+evalComplexity Complexity {..} x =
+  cmplMultiplier * d x ** cmplVarPower * log x ^ cmplLogPower
+
+bestOf :: [(Complexity, Double)] -> Complexity
+bestOf = fst . minimumBy (comparing weigh)
+  where
+    weigh (Complexity {..}, wssr) =
+      wssr
+        * powPenalty
+        -- Penalty for high power of logarithm.
+        * d (max 1 cmplLogPower)
+      where
+        -- Penalty for non-integer power.
+        powPenalty :: Double
+        powPenalty = case abs (cmplVarPower - d (round cmplVarPower)) of
+          0 -> 1
+          -- Severe penalty for almost integer powers
+          diff ->
+            if diff < 0.05
+              then 100
+              else (if diff < 0.15 then 32 else 10)
+
+-- | Represents a time measurement for a given problem's size.
+data Measurement = Measurement
+  { measTime :: !Double
+  , measStDev :: !Double
+  }
+  deriving (Eq, Ord, Generic)
+
+instance Show Measurement where
+  show (Measurement t err) = printf "%.3g ± %.3g" t err
+
+instance NFData Measurement
+
+-- | Guess time complexity from a map where keys
+-- are problem's sizes and values are time measurements (or instruction counts).
+--
+-- >>> :set -XNumDecimals
+-- >>> guessComplexity $ Data.Map.fromList $ map (\(x, t) -> (x, Measurement t 1)) [(2, 4), (3, 10), (4, 15), (5, 25)]
+-- 0.993 * x ^ 2
+-- >>> guessComplexity $ Data.Map.fromList $ map (\(x, t) -> (x, Measurement t 1)) [(1e2, 2.1), (1e3, 2.9), (1e4, 4.1), (1e5, 4.9)]
+-- 0.433 * log x
+--
+-- This function uses following simplifying assumptions:
+--
+-- * All coefficients are non-negative.
+-- * The power of \( \log x \) ('cmplLogPower') is unlikely to be \( > 1 \).
+-- * The power of \( x \) ('cmplVarPower') is unlikely to be fractional.
+--
+-- This function is unsuitable to guess
+-- [superpolynomial](https://en.wikipedia.org/wiki/Time_complexity#Superpolynomial_time)
+-- and higher classes of complexity.
+guessComplexity :: Map Word Measurement -> Complexity
+guessComplexity xys =
+  trace'
+    ("guessComplexity " ++ show (M.assocs xys))
+    bestOf
+    (takeUntilLocalMin cmpls)
+  where
+    cmpls :: Infinite ((Complexity, Double), (Complexity, Double))
+    cmpls = fmap (guessComplexityForFixedLog xys) (0 ...)
+
+    takeUntilLocalMin
+      :: Infinite ((Complexity, Double), (Complexity, Double))
+      -> [(Complexity, Double)]
+    takeUntilLocalMin ((c1, c2) :< (c3, c4) :< cs)
+      | snd c1 > snd c3 || snd c2 > snd c4 =
+          c1 : c2 : takeUntilLocalMin ((c3, c4) :< cs)
+      | otherwise =
+          [c1, c2]
+
+guessComplexityForFixedLog
+  :: Map Word Measurement
+  -> Word
+  -> ((Complexity, Double), (Complexity, Double))
+guessComplexityForFixedLog xys logPow = trace' msg res
+  where
+    -- varPow might be negative here, so always pass it through mkCmpl
+    V2 _ varPow = guessComplexityWithoutLog xys logPow
+    mkCmpl varPow' = guessComplexityForFixedPowAndLog xys varPow' logPow
+    res@((res1, wssr1), (res2, wssr2)) =
+      (mkCmpl (max 0 varPow), mkCmpl (d (round varPow)))
+
+    msg =
+      printf
+        "forFixedLog:\n\t%s, RSS %.4g\n\t%s, RSS %.4g"
+        (show res1)
+        wssr1
+        (show res2)
+        wssr2
+
+guessComplexityWithoutLog :: Map Word Measurement -> Word -> V2
+guessComplexityWithoutLog (M.assocs -> xys) logPow = finish
+  where
+    -- Fit y_i ~ a x_i^b, which is equivalent to log y_i ~ log a + b log x_i.
+    -- This is not ideal, because minimizing the sum of (log y_i - log a - b log x_i) ^ 2
+    -- is not equivalent to minimizing the sum of (y_i - a * x_i^b) ^ 2, but close enough,
+    -- so we are going to use it as a starting point for Levenberg-Marquardt.
+    V2 b0 la0 =
+      linear (\(x, Measurement y _) -> (log x, P.log (y / log x ^ logPow))) xys
+    start = V2 (exp la0) (max 0 b0)
+
+    Fit {fitParams = finish} =
+      NE.last $
+        levenbergMarquardt2WithYerrors
+          ( \(V2 mult varPow) (x, Measurement y err) ->
+              ( y
+              , mult * d x ** varPow * log x ^ logPow
+              , V2
+                  (d x ** varPow * log x ^ logPow)
+                  (mult * d x ** varPow * log x ^ (logPow + 1))
+              , err
+              )
+          )
+          start
+          xys
+
+guessComplexityForFixedPowAndLog
+  :: Map Word Measurement
+  -> Double
+  -> Word
+  -> (Complexity, Double)
+guessComplexityForFixedPowAndLog (M.assocs -> xys) varPow logPow = (res, wssr)
+  where
+    -- We want to find a which minimizes \sum_i (y_i - a f(x_i))^2 for f(x) = x^b * log^c x.
+    -- Then d/da = 0 means that \sum_i (2 a f(x_i)^2 - 2 f(x_i) y_i) = 0
+    -- or equivalently a = \sum_i f(x_i) y_i / \sum_i x_i^2.
+    eval x = d x ** varPow * log x ^ logPow
+    sumXY = sum $ map (\(x, Measurement y _) -> eval x * y) xys
+    sumX2 = sum $ map (\(x, _) -> eval x ** 2) xys
+    start = sumXY / sumX2
+
+    ft =
+      NE.last $
+        levenbergMarquardt1WithYerrors
+          ( \mult (x, Measurement y err) ->
+              ( y
+              , mult * d x ** varPow * log x ^ logPow
+              , d x ** varPow * log x ^ logPow
+              , err
+              )
+          )
+          start
+          xys
+    res =
+      Complexity
+        { cmplMultiplier = fitParams ft
+        , cmplVarPower = varPow
+        , cmplLogPower = logPow
+        }
+    wssr = fitWSSR ft
+
+d :: Word -> Double
+d = fromIntegral
+
+trace' :: String -> b -> b
+#ifdef DEBUG
+trace' = trace
+#else
+trace' = const id
+#endif
diff --git a/tasty-bench-fit.cabal b/tasty-bench-fit.cabal
new file mode 100644
--- /dev/null
+++ b/tasty-bench-fit.cabal
@@ -0,0 +1,63 @@
+cabal-version:   2.0
+name:            tasty-bench-fit
+version:         0.1
+license:         MIT
+license-file:    LICENSE
+maintainer:      andrew.lelechenko@gmail.com
+author:          Bodigrim
+tested-with:
+    ghc ==9.6.1 ghc ==9.4.4 ghc ==9.2.7 ghc ==9.0.2 ghc ==8.10.7
+    ghc ==8.8.4 ghc ==8.6.5 ghc ==8.4.4
+
+homepage:        https://github.com/Bodigrim/tasty-bench-fit
+synopsis:        Determine time complexity of a given function
+description:
+    Benchmark a given function for variable input sizes
+    and find out its time complexity.
+
+category:        Development
+build-type:      Simple
+extra-doc-files:
+    CHANGELOG.md
+    README.md
+
+source-repository head
+    type:     git
+    location: https://github.com/Bodigrim/tasty-bench-fit
+
+flag debug
+    description: Emit ongoing diagnostic information.
+    default:     False
+    manual:      True
+
+library
+    exposed-modules:  Test.Tasty.Bench.Fit
+    hs-source-dirs:   src
+    other-modules:    Test.Tasty.Bench.Fit.Complexity
+    default-language: Haskell2010
+    ghc-options:      -Wall
+    build-depends:
+        base >=4.11 && <5,
+        containers >=0.5.11 && <0.7,
+        deepseq >=1.4 && <1.5,
+        infinite-list >=0.1 && <0.2,
+        tasty >=1.4 && <1.5,
+        tasty-bench >=0.3.4 && <0.4,
+        regression-simple >=0.2.1 && <0.3
+
+    if flag(debug)
+        cpp-options: -DDEBUG
+
+test-suite tasty-bench-fit-test
+    type:             exitcode-stdio-1.0
+    main-is:          Main.hs
+    hs-source-dirs:   test
+    default-language: Haskell2010
+    build-depends:
+        base,
+        containers <0.7,
+        tasty,
+        tasty-bench,
+        tasty-bench-fit,
+        tasty-quickcheck <0.11,
+        tasty-expected-failure <0.13
diff --git a/test/Main.hs b/test/Main.hs
new file mode 100644
--- /dev/null
+++ b/test/Main.hs
@@ -0,0 +1,132 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Main
+  ( main
+  ) where
+
+import Data.List (nub, sort)
+import qualified Data.Map as M
+import Test.Tasty
+import Test.Tasty.Bench (RelStDev(..))
+import Test.Tasty.Bench.Fit
+import Test.Tasty.ExpectedFailure
+import Test.Tasty.QuickCheck
+
+main :: IO ()
+main = defaultMain $ testGroup "All"
+  [ testShow
+  , testGuess
+  , testProperty "sum is linear" $ ioProperty $ do
+    c <- fit $ mkFitConfig (\x -> sum [1..x]) (10, 10000)
+    pure $ counterexample (show c) $ isLinear c
+  -- , testProperty "nub is quadratic" $ ioProperty $ do
+  --   c <- fit $ mkFitConfig (\x -> nub [1..x]) (10, 10000)
+  --   pure $ counterexample (show c) $ isQuadratic c
+  -- , testProperty "sort is linearithmic" $ ioProperty $ do
+  --   c <- fit $ (mkFitConfig (\x -> Data.List.sort $ take (fromIntegral x) $
+  --     iterate (\n -> n * 6364136223846793005 + 1) (1 :: Word)) (10, 100000))
+  --   pure $ counterexample (show c) $ isLinearithmic c
+  ]
+
+testShow :: TestTree
+testShow = testGroup "Show"
+  [ testProperty "Constant" $
+    show (Complexity {cmplMultiplier = 5.978911764705882e-9, cmplVarPower = 0, cmplLogPower = 0}) === "5.98e-9"
+  , testProperty "Logarithmic" $
+    show (Complexity {cmplMultiplier = 5.968840304461118e-8, cmplVarPower = 0, cmplLogPower = 1}) === "5.97e-8 * log x"
+  , testProperty "Logarithmic2" $
+    show (Complexity {cmplMultiplier = 5.793061712300056e-8, cmplVarPower = 0, cmplLogPower = 2}) === "5.79e-8 * (log x) ^ 2"
+  , testProperty "Sqrt" $
+    show (Complexity {cmplMultiplier = 8.974841776295381e-10, cmplVarPower = 0.4690504530830262, cmplLogPower = 0}) === "8.97e-10 * x ^ 0.469"
+  , testProperty "Linear" $
+    show (Complexity {cmplMultiplier = 5.793579541827657e-10, cmplVarPower = 1, cmplLogPower = 0}) === "5.79e-10 * x"
+  , testProperty "Linearithmic" $
+    show (Complexity {cmplMultiplier = 1.354437369864389e-9, cmplVarPower = 1, cmplLogPower = 1}) === "1.35e-9 * x * log x"
+  , testProperty "Linearithmic2" $
+    show (Complexity {cmplMultiplier = 5.754981209362351e-10, cmplVarPower = 1, cmplLogPower = 2}) === "5.75e-10 * x * (log x) ^ 2"
+  , testProperty "Quadratic" $
+    show (Complexity {cmplMultiplier = 5.763471892706858e-10, cmplVarPower = 2, cmplLogPower = 0}) === "5.76e-10 * x ^ 2"
+  , testProperty "Cubic" $
+    show (Complexity {cmplMultiplier = 5.736276961481605e-10, cmplVarPower = 3, cmplLogPower = 0}) === "5.74e-10 * x ^ 3"
+  ]
+
+testGuess :: TestTree
+testGuess = testGroup "Guess"
+  [ testProperty "Constant" $ checkComplexity isConstant
+    [(10,5.881e-9),(15,6.05e-9),(20,6.0e-9),(30,5.938e-9),(40,6.074e-9),(61,6.194e-9),(80,6.282e-9),(122,6.105e-9),(160,6.108e-9),(244,5.927e-9),(320,5.93e-9),(488,5.949e-9),(640,5.9e-9),(976,5.892e-9),(1280,5.918e-9),(1953,5.901e-9),(2560,5.918e-9),(3906,5.947e-9),(5120,5.901e-9),(7812,5.906e-9),(10240,5.907e-9),(15625,5.95e-9),(20480,5.982e-9),(31250,5.993e-9),(40960,5.946e-9),(62500,5.901e-9),(81920,5.922e-9),(125000,5.93e-9),(163840,5.928e-9),(250000,6.228e-9),(327680,5.961e-9),(500000,6.025e-9),(655360,5.929e-9),(1000000,5.96e-9)]
+  , testProperty "Logarithmic" $ checkComplexity isLogarithmic
+    [(10,1.54191e-7),(15,1.7357e-7),(20,1.90191e-7),(30,2.20661e-7),(40,2.31167e-7),(61,2.55251e-7),(80,2.71941e-7),(122,2.97561e-7),(160,3.1158e-7),(244,3.38001e-7),(320,3.50998e-7),(488,3.7589e-7),(640,3.93221e-7),(976,4.15118e-7),(1280,4.30965e-7),(1953,4.5525e-7),(2560,4.70494e-7),(3906,4.98164e-7),(5120,5.1214e-7),(7812,5.50508e-7),(10240,5.51175e-7),(15625,5.75977e-7),(20480,5.98614e-7),(31250,6.14841e-7),(40960,6.32332e-7),(62500,6.60092e-7),(81920,6.67221e-7),(125000,6.94264e-7),(163840,7.08961e-7),(250000,7.3384e-7),(327680,7.48206e-7),(500000,7.75123e-7),(655360,7.90332e-7),(1000000,8.12204e-7)]
+  , testProperty "Logarithmic2" $ checkComplexity isLogarithmic2
+    [(10,3.2606e-7),(15,4.41324e-7),(20,5.44409e-7),(30,6.84828e-7),(40,8.1833e-7),(61,1.017501e-6),(80,1.155663e-6),(122,1.376089e-6),(160,1.527048e-6),(244,1.783776e-6),(320,1.963467e-6),(488,2.255293e-6),(640,2.482833e-6),(976,2.813505e-6),(1280,2.995748e-6),(1953,3.392042e-6),(2560,3.609635e-6),(3906,4.011062e-6),(5120,4.266189e-6),(7812,4.679779e-6),(10240,4.963383e-6),(15625,5.409899e-6),(20480,5.70888e-6),(31250,6.266229e-6),(40960,6.554699e-6),(62500,7.130075e-6),(81920,7.429367e-6),(125000,7.953335e-6),(163840,8.318951e-6),(250000,8.901232e-6),(327680,9.295489e-6),(500000,9.926727e-6),(655360,1.034403e-5),(1000000,1.0997949e-5)]
+  , testProperty "Logarithmic6" $ checkComplexity isLogarithmic6
+    [(10,8.628924e-6),(15,2.2718701e-5),(20,4.1468945e-5),(30,8.90083e-5),(40,1.44395898e-4),(61,2.76677148e-4),(80,4.07342187e-4),(122,7.0664375e-4),(160,9.83112109e-4),(244,1.594223437e-3),(320,2.119596093e-3),(488,3.235329687e-3),(640,4.227651562e-3),(976,6.111234375e-3),(1280,7.672078125e-3),(1953,1.08728375e-2),(2560,1.344470625e-2),(3906,1.8441325e-2),(5120,2.2353e-2),(7812,2.97963125e-2),(10240,3.5516875e-2),(15625,4.6447275e-2),(20480,5.477735e-2),(31250,7.038505e-2),(40960,8.21456e-2),(62500,0.10381915),(81920,0.1200662),(125000,0.1495741),(163840,0.1715495),(250000,0.2110635),(327680,0.2401788),(500000,0.2922768),(655360,0.3303902),(1000000,0.3993154)]
+  , testProperty "Sqrt" $ checkComplexity isSqrt
+    [(10,9.179e-9),(15,9.129e-9),(20,9.721e-9),(30,1.0412e-8),(40,1.0851e-8),(61,1.1441e-8),(80,1.2102e-8),(122,1.3903e-8),(160,1.4497e-8),(244,1.6241e-8),(320,1.746e-8),(488,2.0412e-8),(640,2.2189e-8),(976,2.5812e-8),(1280,2.7865e-8),(1953,3.3284e-8),(2560,3.5825e-8),(3906,4.7608e-8),(5120,5.3362e-8),(7812,6.3584e-8),(10240,7.0786e-8),(15625,8.4566e-8),(20480,9.4943e-8),(31250,1.13772e-7),(40960,1.29419e-7),(62500,1.56251e-7),(81920,1.76977e-7),(125000,2.16214e-7),(163840,2.46864e-7),(250000,3.01931e-7),(327680,3.43224e-7),(500000,4.24035e-7),(655360,4.80871e-7),(1000000,5.90708e-7)]
+  , testProperty "Linear" $ checkComplexity isLinear
+    [(10,1.2137e-8),(19,1.7499e-8),(20,1.8083e-8),(39,2.849e-8),(40,2.9045e-8),(78,5.6604e-8),(80,5.7759e-8),(156,1.01422e-7),(160,1.03728e-7),(312,1.9109e-7),(320,1.962e-7),(625,3.73153e-7),(640,3.81767e-7),(1250,7.34564e-7),(1280,7.49969e-7),(2500,1.469915e-6),(2560,1.505307e-6),(5000,2.896041e-6),(5120,2.967195e-6),(10000,5.777413e-6)]
+  , testProperty "Linearithmic" $ checkComplexity isLinearithmic
+    [(10,2.2405e-8),(19,4.8021e-8),(20,5.0446e-8),(39,9.8831e-8),(40,1.02064e-7),(78,2.13687e-7),(80,2.20389e-7),(156,4.71726e-7),(160,5.15425e-7),(312,1.094096e-6),(320,1.141173e-6),(625,2.407279e-6),(640,2.426035e-6),(1250,5.195858e-6),(1280,5.407168e-6),(2500,1.1405377e-5),(2560,1.1602465e-5),(5000,2.4561621e-5),(5120,2.5307434e-5),(10000,5.5566052e-5)]
+  , testProperty "Linearithmic2" $ checkComplexity isLinearithmic2
+    [(10,4.7181e-8),(19,1.12792e-7),(20,1.22449e-7),(39,3.20318e-7),(40,3.32249e-7),(78,8.75328e-7),(80,9.04648e-7),(156,2.329658e-6),(160,2.419274e-6),(312,6.00791e-6),(320,6.189526e-6),(625,1.5036761e-5),(640,1.5424169e-5),(1250,3.6494995e-5),(1280,3.7753466e-5),(2500,8.7988085e-5),(2560,9.1063623e-5),(5000,2.09651562e-4),(5120,2.13942675e-4),(10000,4.88197265e-4)]
+  , testProperty "Quadratic" $ checkComplexity isQuadratic
+    [(10,6.9102e-8),(15,1.41744e-7),(20,2.42625e-7),(31,5.7397e-7),(40,9.56442e-7),(62,2.248535e-6),(80,3.740179e-6),(125,9.10119e-6),(160,1.4752551e-5),(250,3.5977856e-5),(320,5.9150854e-5),(500,1.44069628e-4),(640,2.36670605e-4),(1000,5.76093359e-4)]
+  , testProperty "Quadrithmic4" $ checkComplexity isQuadrithmic4
+    [(5,3.5023e-8),(9,1.59489e-7),(10,2.12688e-7),(19,1.627995e-6),(20,1.919146e-6),(39,1.5753015e-5),(40,1.704226e-5),(78,1.25921337e-4),(80,1.35570312e-4),(156,9.08977343e-4),(160,9.75295703e-4),(312,6.07931875e-3),(320,6.496996875e-3),(625,3.86003e-2),(640,4.0853375e-2),(1250,0.2314005),(1280,0.2456381),(2500,1.339004),(2560,1.4231234),(5000,7.528904)]
+  , testProperty "Cubic" $ checkComplexity isCubic
+    [(10,5.98066e-7),(11,7.7601e-7),(20,4.609741e-6),(23,6.99185e-6),(40,3.6676177e-5),(46,5.5854089e-5),(80,2.92877148e-4),(93,4.66834472e-4),(160,2.344111718e-3),(187,3.740370312e-3),(320,1.8751396875e-2),(375,3.018281875e-2),(640,0.150031325),(750,0.2414234),(1280,1.1982404),(1500,1.9280254),(2560,9.5926602),(3000,15.4408018)]
+  , testProperty "Quartic" $ checkComplexity isQuartic
+    [(5,1.6603e-8),(7,3.0392e-8),(10,9.1955e-8),(15,3.25706e-7),(20,9.76705e-7),(31,5.34298e-6),(40,1.472517e-5),(62,8.4625488e-5),(80,2.34295019e-4),(125,1.395396875e-3),(160,3.74655e-3),(250,2.23739875e-2),(320,6.0027625e-2),(500,0.357446),(640,0.9591132),(1000,5.725087)]
+
+  , testProperty "Karatsuba" $ checkComplexity isKaratsuba
+    [(10,4.8364e-8),(12,6.0228e-8),(20,9.9186e-8),(24,1.21309e-7),(40,2.31972e-7),(48,2.9911e-7),(80,6.2843e-7),(97,8.46736e-7),(160,1.846619e-6),(195,2.503655e-6),(320,5.42057e-6),(390,7.376403e-6),(640,1.6124441e-5),(781,2.2078021e-5),(1280,4.8210919e-5),(1562,6.6098962e-5),(2560,1.44684423e-4),(3125,1.98921875e-4),(5120,4.34806054e-4),(6250,5.9602539e-4),(10240,1.301581445e-3),(12500,1.784770312e-3),(20480,3.903389843e-3),(25000,5.354964062e-3),(40960,1.171065625e-2),(50000,1.604174375e-2),(81920,3.509155625e-2),(100000,4.82393125e-2)]
+  , testProperty "Strassen" $ checkComplexity isStrassen
+    [(10,4.02343e-7),(11,5.14162e-7),(20,2.64022e-6),(23,3.884503e-6),(40,1.8058444e-5),(46,2.6682556e-5),(80,1.258875e-4),(93,1.92064208e-4),(160,8.8356914e-4),(187,1.362714843e-3),(320,6.163835937e-3),(375,9.710895312e-3),(640,4.32488375e-2),(750,6.8603265625e-2),(1280,0.30328925),(1500,0.4761277),(2560,2.1247246),(3000,3.3290002)]
+
+  , testProperty "Linear again" $ checkComplexity isLinear
+    [(1,6.9753e-8),(2,1.28492e-7),(4,2.46261e-7),(5,3.05419e-7),(8,4.82596e-7),(10,6.01227e-7)]
+  ]
+
+checkComplexity :: (Complexity -> Bool) -> [(Word, Double)] -> Property
+checkComplexity p xys = counterexample (show cmpl) (p cmpl)
+  where
+    cmpl = guessComplexity $ fmap (`Measurement` 1) $ M.fromList xys
+
+isSqrt :: Complexity -> Bool
+isSqrt = \case
+  Complexity {cmplVarPower = varPow, cmplLogPower = 0} -> varPow > 0.4 && varPow < 0.6
+  _ -> False
+
+isLogarithmic2 :: Complexity -> Bool
+isLogarithmic2 = \case
+  Complexity {cmplVarPower = 0, cmplLogPower = 2} -> True
+  _ -> False
+
+isLogarithmic6 :: Complexity -> Bool
+isLogarithmic6 = \case
+  Complexity {cmplVarPower = 0, cmplLogPower = 6} -> True
+  _ -> False
+
+isLinearithmic2 :: Complexity -> Bool
+isLinearithmic2 = \case
+  Complexity {cmplVarPower = 1, cmplLogPower = 2} -> True
+  _ -> False
+
+isQuadrithmic4 :: Complexity -> Bool
+isQuadrithmic4 = \case
+  Complexity {cmplVarPower = 2, cmplLogPower = 4} -> True
+  _ -> False
+
+isQuartic :: Complexity -> Bool
+isQuartic = \case
+  Complexity {cmplVarPower = 4, cmplLogPower = 0} -> True
+  _ -> False
+
+isKaratsuba :: Complexity -> Bool
+isKaratsuba = \case
+  Complexity {cmplVarPower = varPow, cmplLogPower = 0} -> varPow > 1.5 && varPow < 1.7
+  _ -> False
+
+isStrassen :: Complexity -> Bool
+isStrassen = \case
+  Complexity {cmplVarPower = varPow, cmplLogPower = 0} -> varPow > 2.7 && varPow < 2.9
+  _ -> False
