{ {-*- haskell -*-}
--------------------------------------------------------------------
-- |
-- Module : Data.ByteString.Lex.Double
-- Copyright : (c) Galois, Inc. 2008
-- License : All rights reserved
--
-- Maintainer: Don Stewart <dons@galois.com>
-- Stability : provisional
-- Portability:
--
--------------------------------------------------------------------
--
-- Efficiently parse floating point literals from a ByteString
--
module Data.ByteString.Lex.Double ( readDouble, unsafeReadDouble ) where
import qualified Data.ByteString as B
import Data.ByteString.Internal
import Data.ByteString.Lex.Internal (strtod)
import qualified Data.ByteString.Unsafe as B
import Foreign
import Foreign.C.Types
import Foreign.C.String
}
%wrapper "strict-bytestring"
$space = [\ \t\xa0]
$digit = 0-9
$octit = 0-7
$hexit = [$digit A-F a-f]
@sign = [\-\+]
@decimal = $digit+
@octal = $octit+
@hexadecimal = $hexit+
@exponent = [eE] [\-\+]? @decimal
@number = @decimal
| @decimal \. @decimal @exponent?
| @decimal @exponent
| 0[oO] @octal
| 0[xX] @hexadecimal
lex :-
@sign? @number { strtod }
{
-- | Parse the initial portion of the ByteString as a Double precision
-- floating point value. The expected form of the numeric literal is
-- given by:
--
-- * An optional '+' or '-' sign
--
-- * Decimal digits, OR
--
-- * 0 [oO] and a sequence of octal digits, OR
--
-- * 0 [xX] and a sequence of hexadecimal digits, OR
--
-- * An optional decimal point, followed by a sequence of decimal digits,
--
-- * And an optional exponent
--
-- The result is returned as a pair of a double-precisoin floating point
-- value, and the remaining input, or Nothing, should no parse be found.
--
-- For example, to sum a file of floating point numbers, one per line,
--
-- > import qualified Data.ByteString.Char8 as S
-- > import qualified Data.ByteString.Unsafe as S
-- > import Data.ByteString.Lex.Double
-- >
-- > main = print . go 0 =<< S.getContents
-- > where
-- > go n s = case readDouble s of
-- > Nothing -> n
-- > Just (k,rest) -> go (n+k) (S.tail rest)
--
readDouble :: ByteString -> Maybe (Double, ByteString)
readDouble str = case alexScan (AlexInput '\n' str) 0 of
AlexEOF -> Nothing
AlexError _ -> Nothing
AlexToken (AlexInput _ rest) n _ ->
case my_strtod (B.unsafeTake n str) of d -> d `seq` Just $! (d , rest)
-- Safe, minimal copy of substring identified by Alex.
my_strtod :: ByteString -> Double
my_strtod b = inlinePerformIO $ B.useAsCString b $ \ptr -> c_strtod ptr nullPtr
{-# INLINE my_strtod #-}
foreign import ccall unsafe "stdlib.h strtod"
c_strtod :: CString -> Ptr CString -> IO Double
------------------------------------------------------------------------
--
-- | Bare bones, unsafe wrapper for strtod. This provides a non-copying
-- direct parsing of Double values from a ByteString. It uses strtod
-- directly on the bytestring buffer. strtod requires the string to be
-- null terminated, or for a guarantee that parsing will find a floating
-- point value before the end of the string.
--
unsafeReadDouble :: ByteString -> Maybe (Double, ByteString)
unsafeReadDouble b | B.null b = Nothing
unsafeReadDouble b = inlinePerformIO $
alloca $ \resptr ->
B.unsafeUseAsCString b $ \ptr -> do -- copy just the bytes we want to parse
-- resetErrno
d <- c_strtod ptr resptr --
-- err <- getErrno
newPtr <- peek resptr
return $! case d of
0 | newPtr == ptr -> Nothing
-- _ | err == eRANGE -> Nothing -- adds 10% overhead
_ | otherwise ->
let rest = B.unsafeDrop (newPtr `minusPtr` ptr) b
z = realToFrac d
in z `seq` rest `seq` Just $! (z, rest)
{-# INLINE unsafeReadDouble #-}
}