We can easily add this function to ghc-bignum.

I've opened https://gitlab.haskell.org/ghc/ghc/-/issues/18697 to track this.

Sylvain

On 16/09/2020 04:19, Keith wrote:

The short of it is,

clampNaturalToWord :: Natural → Word
clampNaturalToWord n = case n of
NatS# w -> W# w
_ -> maxBound

results in much better space and time use than naturalToWord, which always takes the least significant Word of the Natural.

Because naturalToWord takes the least significant Word, you always have to check for size before conversion. Even though you do check, GHC has to assume that, after conversion, the big Natural could have resulted in a small Word and will uselessly duplicate all branches for both cases.

Is there anything wrong with clamping by default in this case?

--Keith

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