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|
{-# LANGUAGE CPP, MagicHash, Rank2Types #-}
-- |
-- Module : Data.Double.Conversion.Text
-- Copyright : (c) 2011 MailRank, Inc.
--
-- License : BSD-style
-- Maintainer : bos@serpentine.com
-- Stability : experimental
-- Portability : GHC
--
-- Fast, efficient support for converting between double precision
-- floating point values and text.
--
-- These functions are about 30 times faster than the default 'show'
-- implementation for the 'Double' type.
module Data.Double.Conversion.Text
(
toExponential
, toFixed
, toPrecision
, toShortest
) where
import Control.Monad (when)
#if MIN_VERSION_base(4,4,0)
import Control.Monad.ST.Unsafe (unsafeIOToST)
#else
import Control.Monad.ST (unsafeIOToST)
#endif
import Control.Monad.ST (runST)
import Data.Double.Conversion.FFI
import Data.Text.Internal (Text(Text))
import Foreign.C.Types (CDouble, CInt)
import GHC.Prim (MutableByteArray#)
import qualified Data.Text.Array as A
-- | Compute a representation in exponential format with the requested
-- number of digits after the decimal point. The last emitted digit is
-- rounded. If -1 digits are requested, then the shortest exponential
-- representation is computed.
toExponential :: Int -> Double -> Text
toExponential ndigits = convert "toExponential" len $ \val mba ->
c_Text_ToExponential val mba (fromIntegral ndigits)
where len = c_ToExponentialLength
{-# NOINLINE len #-}
-- | Compute a decimal representation with a fixed number of digits
-- after the decimal point. The last emitted digit is rounded.
toFixed :: Int -> Double -> Text
toFixed ndigits = convert "toFixed" len $ \val mba ->
c_Text_ToFixed val mba (fromIntegral ndigits)
where len = c_ToFixedLength
{-# NOINLINE len #-}
-- | Compute the shortest string of digits that correctly represent
-- the input number.
toShortest :: Double -> Text
toShortest = convert "toShortest" len c_Text_ToShortest
where len = c_ToShortestLength
{-# NOINLINE len #-}
-- | Compute @precision@ leading digits of the given value either in
-- exponential or decimal format. The last computed digit is rounded.
toPrecision :: Int -> Double -> Text
toPrecision ndigits = convert "toPrecision" len $ \val mba ->
c_Text_ToPrecision val mba (fromIntegral ndigits)
where len = c_ToPrecisionLength
{-# NOINLINE len #-}
convert :: String -> CInt
-> (forall s. CDouble -> MutableByteArray# s -> IO CInt)
-> Double -> Text
convert func len act val = runST go
where
go = do
buf <- A.new (fromIntegral len)
size <- unsafeIOToST $ act (realToFrac val) (A.maBA buf)
when (size == -1) .
fail $ "Data.Double.Conversion.Text." ++ func ++
": conversion failed (invalid precision requested)"
frozen <- A.unsafeFreeze buf
return $ Text frozen 0 (fromIntegral size)
|
