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module Algo.FindIndexR (findIndexR, findIndexR_naive, findIndexR_manual)
where
import Data.Vector.Unboxed (Vector)
import qualified Data.Vector.Generic as V
findIndexR :: (Double -> Bool, Vector Double) -> Maybe Int
{-# NOINLINE findIndexR #-}
findIndexR = uncurry V.findIndexR
findIndexR_naive :: (Double -> Bool, Vector Double) -> Maybe Int
{-# NOINLINE findIndexR_naive #-}
findIndexR_naive (pred, v) = fmap (V.length v - 1 -)
$ V.foldl (\a x -> if pred x
then Just 1
else succ<$>a) Nothing v
findIndexR_manual :: (Double -> Bool, Vector Double) -> Maybe Int
{-# NOINLINE findIndexR_manual #-}
findIndexR_manual (pred, v) = go $ V.length v - 1
where go i | i < 0 = Nothing
| pred (V.unsafeIndex v i) = Just i
| otherwise = go $ i-1
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