stringsearch-0.3.6.1: Data/ByteString/Lazy/Search/DFA.hs
{-# LANGUAGE BangPatterns #-}
-- |
-- Module : Data.ByteString.Lazy.Search.DFA
-- Copyright : Daniel Fischer
-- Licence : BSD3
-- Maintainer : Daniel Fischer <daniel.is.fischer@googlemail.com>
-- Stability : Provisional
-- Portability : non-portable (BangPatterns)
--
-- Fast search of lazy 'L.ByteString' values. Breaking,
-- splitting and replacing using a deterministic finite automaton.
module Data.ByteString.Lazy.Search.DFA ( -- * Overview
-- $overview
-- ** Complexity and performance
-- $complexity
-- ** Partial application
-- $partial
-- * Finding substrings
indices
, nonOverlappingIndices
-- * Breaking on substrings
, breakOn
, breakAfter
, breakFindAfter
-- * Replacing
, replace
-- * Splitting
, split
, splitKeepEnd
, splitKeepFront
) where
import Data.ByteString.Search.Internal.Utils (automaton, keep, ldrop, lsplit)
import Data.ByteString.Search.Substitution
import qualified Data.ByteString as S
import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Lazy.Internal as LI
import Data.ByteString.Unsafe (unsafeIndex)
import Data.Array.Base (unsafeAt)
--import Data.Array.Unboxed (UArray)
import Data.Bits
import Data.Int (Int64)
-- $overview
--
-- This module provides functions related to searching a substring within
-- a string. The searching algorithm uses a deterministic finite automaton
-- based on the Knuth-Morris-Pratt algorithm.
-- The automaton is implemented as an array of @(patternLength + 1) * σ@
-- state transitions, where σ is the alphabet size (256), so it is only
-- suitable for short enough patterns, therefore the patterns in this module
-- are required to be strict 'S.ByteString's.
--
-- When searching a pattern in a UTF-8-encoded 'L.ByteString', be aware that
-- these functions work on bytes, not characters, so the indices are
-- byte-offsets, not character offsets.
-- $complexity
--
-- The time and space complexity of the preprocessing phase is
-- /O/(@patternLength * σ@).
-- The searching phase is /O/(@targetLength@), each target character is
-- inspected only once.
--
-- In general the functions in this module have about the same performance as
-- the corresponding functions using the Knuth-Morris-Pratt algorithm but
-- are considerably slower than the Boyer-Moore functions. For very short
-- patterns or, in the case of 'indices', patterns with a short period
-- which occur often, however, times are close to or even below the
-- Boyer-Moore times.
-- $partial
--
-- All functions can usefully be partially applied. Given only a pattern,
-- the automaton is constructed only once, allowing efficient re-use.
------------------------------------------------------------------------------
-- Exported Functions --
------------------------------------------------------------------------------
-- | @'indices'@ finds the starting indices of all possibly overlapping
-- occurrences of the pattern in the target string.
-- If the pattern is empty, the result is @[0 .. 'length' target]@.
{-# INLINE indices #-}
indices :: S.ByteString -- ^ Strict pattern to find
-> L.ByteString -- ^ Lazy string to search
-> [Int64] -- ^ Offsets of matches
indices !pat = lazySearcher True pat . L.toChunks
-- | @'nonOverlappingIndices'@ finds the starting indices of all
-- non-overlapping occurrences of the pattern in the target string.
-- It is more efficient than removing indices from the list produced
-- by 'indices'.
{-# INLINE nonOverlappingIndices #-}
nonOverlappingIndices :: S.ByteString -- ^ Strict pattern to find
-> L.ByteString -- ^ Lazy string to search
-> [Int64] -- ^ Offsets of matches
nonOverlappingIndices !pat = lazySearcher False pat . L.toChunks
-- | @'breakOn' pattern target@ splits @target@ at the first occurrence
-- of @pattern@. If the pattern does not occur in the target, the
-- second component of the result is empty, otherwise it starts with
-- @pattern@. If the pattern is empty, the first component is empty.
-- For a non-empty pattern, the first component is generated lazily,
-- thus the first parts of it can be available before the pattern has
-- been found or determined to be absent.
--
-- @
-- 'uncurry' 'L.append' . 'breakOn' pattern = 'id'
-- @
breakOn :: S.ByteString -- ^ Strict pattern to search for
-> L.ByteString -- ^ Lazy string to search in
-> (L.ByteString, L.ByteString)
-- ^ Head and tail of string broken at substring
breakOn pat = breaker . L.toChunks
where
lbrk = lazyBreaker True pat
breaker strs = let (f, b) = lbrk strs
in (L.fromChunks f, L.fromChunks b)
-- | @'breakAfter' pattern target@ splits @target@ behind the first occurrence
-- of @pattern@. An empty second component means that either the pattern
-- does not occur in the target or the first occurrence of pattern is at
-- the very end of target. If you need to discriminate between those cases,
-- use breakFindAfter.
-- If the pattern is empty, the first component is empty.
-- For a non-empty pattern, the first component is generated lazily,
-- thus the first parts of it can be available before the pattern has
-- been found or determined to be absent.
-- @
-- 'uncurry' 'L.append' . 'breakAfter' pattern = 'id'
-- @
breakAfter :: S.ByteString -- ^ Strict pattern to search for
-> L.ByteString -- ^ Lazy string to search in
-> (L.ByteString, L.ByteString)
-- ^ Head and tail of string broken after substring
breakAfter pat = breaker . L.toChunks
where
lbrk = lazyBreaker False pat
breaker strs = let (f, b) = lbrk strs
in (L.fromChunks f, L.fromChunks b)
-- | @'breakFindAfter'@ does the same as 'breakAfter' but additionally indicates
-- whether the pattern is present in the target.
--
-- @
-- 'fst' . 'breakFindAfter' pat = 'breakAfter' pat
-- @
breakFindAfter :: S.ByteString -- ^ Strict pattern to search for
-> L.ByteString -- ^ Lazy string to search in
-> ((L.ByteString, L.ByteString), Bool)
-- ^ Head and tail of string broken after substring
-- and presence of pattern
breakFindAfter pat
| S.null pat = \str -> ((L.empty, str), True)
breakFindAfter pat = breaker . L.toChunks
where
!patLen = S.length pat
lbrk = lazyBreaker True pat
breaker strs = let (f, b) = lbrk strs
(f1, b1) = lsplit patLen b
mbpat = L.fromChunks f1
in ((foldr LI.chunk mbpat f, L.fromChunks b1), not (null b))
-- | @'replace' pat sub text@ replaces all (non-overlapping) occurrences of
-- @pat@ in @text@ with @sub@. If occurrences of @pat@ overlap, the first
-- occurrence that does not overlap with a replaced previous occurrence
-- is substituted. Occurrences of @pat@ arising from a substitution
-- will not be substituted. For example:
--
-- @
-- 'replace' \"ana\" \"olog\" \"banana\" = \"bologna\"
-- 'replace' \"ana\" \"o\" \"bananana\" = \"bono\"
-- 'replace' \"aab\" \"abaa\" \"aaabb\" = \"aabaab\"
-- @
--
-- The result is a lazy 'L.ByteString',
-- which is lazily produced, without copying.
-- Equality of pattern and substitution is not checked, but
--
-- @
-- 'replace' pat pat text == text
-- @
--
-- holds (the internal structure is generally different).
-- If the pattern is empty but not the substitution, the result
-- is equivalent to (were they 'String's) @cycle sub@.
--
-- For non-empty @pat@ and @sub@ a lazy 'L.ByteString',
--
-- @
-- 'L.concat' . 'Data.List.intersperse' sub . 'split' pat = 'replace' pat sub
-- @
--
-- and analogous relations hold for other types of @sub@.
replace :: Substitution rep
=> S.ByteString -- ^ Strict pattern to replace
-> rep -- ^ Replacement string
-> L.ByteString -- ^ Lazy string to modify
-> L.ByteString -- ^ Lazy result
replace pat
| S.null pat = \sub -> prependCycle sub
| otherwise =
let !patLen = S.length pat
breaker = lazyBreaker True pat
repl subst strs
| null strs = []
| otherwise =
let (pre, mtch) = breaker strs
in pre ++ case mtch of
[] -> []
_ -> subst (repl subst (ldrop patLen mtch))
in \sub -> let {-# NOINLINE subst #-}
!subst = substitution sub
repl1 = repl subst
in L.fromChunks . repl1 . L.toChunks
-- | @'split' pattern target@ splits @target@ at each (non-overlapping)
-- occurrence of @pattern@, removing @pattern@. If @pattern@ is empty,
-- the result is an infinite list of empty 'L.ByteString's, if @target@
-- is empty but not @pattern@, the result is an empty list, otherwise
-- the following relations hold (where @patL@ is the lazy 'L.ByteString'
-- corresponding to @pat@):
--
-- @
-- 'L.concat' . 'Data.List.intersperse' patL . 'split' pat = 'id',
-- 'length' ('split' pattern target) ==
-- 'length' ('nonOverlappingIndices' pattern target) + 1,
-- @
--
-- no fragment in the result contains an occurrence of @pattern@.
split :: S.ByteString -- ^ Strict pattern to split on
-> L.ByteString -- ^ Lazy string to split
-> [L.ByteString] -- ^ Fragments of string
split pat
| S.null pat = const (repeat L.empty)
split pat = map L.fromChunks . splitter . L.toChunks
where
!patLen = S.length pat
breaker = lazyBreaker True pat
splitter strs
| null strs = []
| otherwise = splitter' strs
splitter' strs
| null strs = [[]]
| otherwise =
case breaker strs of
(pre, mtch) ->
pre : case mtch of
[] -> []
_ -> splitter' (ldrop patLen mtch)
-- | @'splitKeepEnd' pattern target@ splits @target@ after each (non-overlapping)
-- occurrence of @pattern@. If @pattern@ is empty, the result is an
-- infinite list of empty 'L.ByteString's, otherwise the following
-- relations hold:
--
-- @
-- 'L.concat' . 'splitKeepEnd' pattern = 'id,'
-- @
--
-- all fragments in the result except possibly the last end with
-- @pattern@, no fragment contains more than one occurrence of @pattern@.
splitKeepEnd :: S.ByteString -- ^ Strict pattern to split on
-> L.ByteString -- ^ Lazy string to split
-> [L.ByteString] -- ^ Fragments of string
splitKeepEnd pat
| S.null pat = const (repeat L.empty)
splitKeepEnd pat = map L.fromChunks . splitter . L.toChunks
where
breaker = lazyBreaker False pat
splitter [] = []
splitter strs =
case breaker strs of
(pre, mtch) -> pre : splitter mtch
-- | @'splitKeepFront'@ is like 'splitKeepEnd', except that @target@ is split
-- before each occurrence of @pattern@ and hence all fragments
-- with the possible exception of the first begin with @pattern@.
-- No fragment contains more than one non-overlapping occurrence
-- of @pattern@.
splitKeepFront :: S.ByteString -- ^ Strict pattern to split on
-> L.ByteString -- ^ Lazy string to split
-> [L.ByteString] -- ^ Fragments of string
splitKeepFront pat
| S.null pat = const (repeat L.empty)
splitKeepFront pat = map L.fromChunks . splitter . L.toChunks
where
!patLen = S.length pat
breaker = lazyBreaker True pat
splitter strs = case splitter' strs of
([] : rst) -> rst
other -> other
splitter' [] = []
splitter' strs =
case breaker strs of
(pre, mtch) ->
pre : case mtch of
[] -> []
_ -> case lsplit patLen mtch of
(pt, rst) ->
if null rst
then [pt]
else let (h : t) = splitter' rst
in (pt ++ h) : t
------------------------------------------------------------------------------
-- Searching Function --
------------------------------------------------------------------------------
lazySearcher :: Bool -> S.ByteString -> [S.ByteString] -> [Int64]
lazySearcher _ !pat
| S.null pat =
let zgo _ [] = []
zgo !prior (!str : rest) =
let !l = S.length str
!prior' = prior + fromIntegral l
in [prior + fromIntegral i | i <- [1 .. l]] ++ zgo prior' rest
in (0:) . zgo 0
| S.length pat == 1 =
let !w = S.head pat
ixes = S.elemIndices w
go _ [] = []
go !prior (!str : rest)
= let !prior' = prior + fromIntegral (S.length str)
in map ((+ prior) . fromIntegral) (ixes str) ++ go prior' rest
in go 0
lazySearcher !overlap pat = search 0 0
where
!patLen = S.length pat
!auto = automaton pat
!p0 = unsafeIndex pat 0
!ams = if overlap then patLen else 0
search _ _ [] = []
search !prior st (!str:rest) = match st 0
where
!strLen = S.length str
{-# INLINE strAt #-}
strAt :: Int -> Int
strAt i = fromIntegral (str `unsafeIndex` i)
match 0 !idx
| idx == strLen = search (prior + fromIntegral strLen) 0 rest
| unsafeIndex str idx == p0 = match 1 (idx + 1)
| otherwise = match 0 (idx + 1)
match state idx
| idx == strLen = search (prior + fromIntegral strLen) state rest
| otherwise =
let nstate = unsafeAt auto ((state `shiftL` 8) + strAt idx)
!nxtIdx = idx + 1
in if nstate == patLen
then (prior + fromIntegral (nxtIdx - patLen)) :
match ams nxtIdx
else match nstate nxtIdx
------------------------------------------------------------------------------
-- Breaking --
------------------------------------------------------------------------------
-- Code duplication :(
-- Needed for reasonable performance.
lazyBreaker :: Bool -> S.ByteString -> [S.ByteString]
-> ([S.ByteString], [S.ByteString])
lazyBreaker before pat
| S.null pat = \strs -> ([], strs)
| S.length pat == 1 =
let !w = S.head pat
!a = if before then 0 else 1
ixes = S.elemIndices w
scan [] = ([], [])
scan (!str:rest) =
let !strLen = S.length str
in case ixes str of
[] -> let (fr, bk) = scan rest in (str : fr, bk)
(i:_) -> let !j = i + a
in if j == strLen
then ([str],rest)
else ([S.take j str], S.drop j str : rest)
in scan
lazyBreaker !before pat = bscan [] 0
where
!patLen = S.length pat
!auto = automaton pat
!p0 = unsafeIndex pat 0
bscan _ _ [] = ([], [])
bscan !past !sta (!str:rest) = match sta 0
where
!strLen = S.length str
{-# INLINE strAt #-}
strAt :: Int -> Int
strAt i = fromIntegral (str `unsafeIndex` i)
match 0 idx
| idx == strLen =
let (fr, bk) = bscan [] 0 rest
in (foldr (flip (.) . (:)) id past (str:fr), bk)
| unsafeIndex str idx == p0 = match 1 (idx + 1)
| otherwise = match 0 (idx + 1)
match state idx
| idx == strLen =
let (kp, !rl) = if before
then keep state (str:past)
else ([], str:past)
(fr, bk) = bscan kp state rest
in (foldr (flip (.) . (:)) id rl fr, bk)
| otherwise =
let !nstate = unsafeAt auto ((state `shiftL` 8) + strAt idx)
!nxtIdx = idx + 1
in if nstate == patLen
then case if before then nxtIdx - patLen else nxtIdx of
0 -> (foldr (flip (.) . (:)) id past [], str:rest)
stIx | stIx < 0 -> rgo (-stIx) (str:rest) past
| stIx == strLen ->
(foldr (flip (.) . (:)) id past [str],rest)
| otherwise ->
(foldr (flip (.) . (:)) id past
[S.take stIx str], S.drop stIx str : rest)
else match nstate nxtIdx
-- Did I already mention that I suck at finding names?
{-# INLINE rgo #-}
rgo :: Int -> [S.ByteString] -> [S.ByteString]
-> ([S.ByteString], [S.ByteString])
rgo !kp acc (!str:more)
| sl == kp = (reverse more, str:acc)
| sl < kp = rgo (kp - sl) (str:acc) more
| otherwise = case S.splitAt (sl - kp) str of
(fr, bk) ->
(foldr (flip (.) . (:)) id more [fr], bk:acc)
where
!sl = S.length str
rgo _ _ [] = error "Not enough past!"
-- If that error is ever encountered, I screwed up badly.