[Haskell-cafe] faster faster faster but not uglier (how to make nice code AND nice core)?

[Henning Thielemann]

On Wed, 19 May 2021, Johannes Waldmann wrote:

> I wanted a really fast implementation of a vector addition system
> where the "vector" contains small numbers only.

With integer elements?

> and  I want it packed into a machine word
> (and finally put these into Data.IntSet).

Why not using Integer? With a bit of bit tricks you can implement a vector 
add via Integer addition.
   https://en.wikipedia.org/wiki/SWAR

E.g. like this

   vectorAdd x y =
      maskOddElements (maskOddElements x + maskOddElements y)
      +
      maskEvenElements (maskEvenElements x + maskEvenElements y)

But I suspect that larger Integers are not hold in registers.

Chances are better for a record of Word8's, Word16's ...
Maybe if they are put in a compact region:
   http://hackage.haskell.org/package/ghc-compact


Or you use the CPU vector types that GHC provides.
   http://hackage.haskell.org/package/ghc-prim-0.7.0/docs/GHC-Prim.html#g:35

There seem to be some packages for small vectors:
   https://hackage.haskell.org/package/compact-word-vectors
   https://hackage.haskell.org/package/smallarray