findIndicesEnd

haskell · Jul 3, 2018 · b8a0a8a · b8a0a8a
1 parent f061966
commit b8a0a8a
Showing 1 changed file with 10 additions and 0 deletions.
diff --git a/Data/ByteString.hs b/Data/ByteString.hs
@@ -158,6 +158,7 @@ module Data.ByteString (
         findIndex,              -- :: (Word8 -> Bool) -> ByteString -> Maybe Int
         findIndices,            -- :: (Word8 -> Bool) -> ByteString -> [Int]
         findIndexEnd,           -- :: (Word8 -> Bool) -> ByteString -> Maybe Int
+        findIndicesEnd,         -- :: (Word8 -> Bool) -> ByteString -> [Int]
         count,                  -- :: Word8 -> ByteString -> Int
 
         -- * Zipping and unzipping ByteStrings
@@ -1170,6 +1171,15 @@ findIndices p ps = loop 0 ps
                  | p (unsafeHead qs) = n : loop (n+1) (unsafeTail qs)
                  | otherwise         =     loop (n+1) (unsafeTail qs)
 
+-- | The 'findIndicesEnd' function extends 'findIndexEnd', by returning the
+-- indices of all elements satisfying the predicate, in ascending order.
+findIndicesEnd :: (Word8 -> Bool) -> ByteString -> [Int]
+findIndicesEnd p ps = loop (length ps - 1) ps
+   where
+     loop !n !qs | null qs           = []
+                 | p (unsafeLast qs) = n : loop (n-1) (unsafeInit qs)
+                 | otherwise         =     loop (n-1) (unsafeInit qs)
+
 -- ---------------------------------------------------------------------
 -- Searching ByteStrings