Optimizing numerical array performance in Haskell

Question

I\'m working on a terrain generation algorithm for a MineCraft-like world. Currently, I\'m using simplex noise based on the implementation in the paper \'Simplex Noise Demys

Answer 1

The thing that stands out initially is that your code is highly polymorphic. You should specialize your floating point type uniformly to Double, so GHC (and LLVM) have a chance of applying more aggressive optimizations.

Note, for those trying to reproduce, this code imports:

import qualified Data.Vector as V
import Data.Bits
import Data.Time.Clock
import System.Random
import System.Random.Shuffle

type Permutation = V.Vector Int

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Ok. There's lots of things you can try to improve this code.

Improvements

Data representation

• Specialize to a concrete floating point type, instead of polymorphic floating point functions
• Replace tuple (a,a,a) with unboxed triple T !Double !Double !Double
• Switch from Data.Array to Data.Array.Unboxed for Permutations
• Replace use of boxed array of triples with multidimensional unboxed array from repa package

Compiler flags

• Compile with -O2 -fvia-C -optc-O3 -fexcess-precision -optc-march=native (or equivalent with -fllvm)
• Increase spec constr threshold -- -fspec-constr-count=16

More efficient library functions

• Use mersenne-random instead of StdGen to generate randoms
• Replace mod with rem
• Replace V.! indexing with unchecked indexing VU.unsafeIndex (after moving to Data.Vector.Unboxed

Runtime settings

• Increase the default allocation area: -A20M or -H

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Also, check your algorithm is identical to the C# one, and you're using the same data structures.