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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeOperators #-}
{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
module Util where
import qualified Data.Array.RankedS as OR
import GHC.TypeLits
import Data.Array.Mixed (fromSNat')
import Data.Array.Nested
-- Returns highest value that satisfies the predicate, or `lo` if none does
binarySearch :: (Num a, Eq a) => (a -> a) -> a -> a -> (a -> Bool) -> a
binarySearch div2 = \lo hi f -> case (f lo, f hi) of
(False, _) -> lo
(_, True) -> hi
(_, _ ) -> go lo hi f
where
go lo hi f = -- invariant: f lo && not (f hi)
let mid = lo + div2 (hi - lo)
in if mid `elem` [lo, hi]
then mid
else if f mid then go mid hi f else go lo mid f
orSumOuter1 :: (OR.Unbox a, Num a) => SNat n -> OR.Array (n + 1) a -> OR.Array n a
orSumOuter1 (sn@SNat :: SNat n) =
let n = fromSNat' sn
in OR.rerank @n @1 @0 (OR.scalar . OR.sumA) . OR.transpose ([1 .. n] ++ [0])
rshTail :: ShR (n + 1) i -> ShR n i
rshTail (_ :$: sh) = sh
rshTail ZSR = error "unreachable"
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