added an explicit exponent sign got FGeneric and FScientific so that …

…a + will prepend the exponent digits if positive

Data/ByteString/Builder/RealFloat.hs

@@ -79,6 +79,7 @@ module Data.ByteString.Builder.RealFloat
   , standardDefaultPrecision
   , scientific
   , scientificZeroPaddedExponent
+  , scientificExplicitExponentSign
   , generic
   ) where
 
@@ -143,7 +144,7 @@ standardDefaultPrecision = FStandard
 --
 -- @since 0.11.2.0
 scientific :: FloatFormat a
-scientific = fScientific 'e' scientificSpecialStrings False
+scientific = fScientific 'e' scientificSpecialStrings False False
 
 -- | Like @scientific@ but has a zero padded exponent.
 scientificZeroPaddedExponent :: forall a. ZeroPadCount a => FloatFormat a
@@ -157,6 +158,17 @@ scientificZeroPaddedExponent = scientific
   where
   positiveZero = "0.0e" <> replicate (zeroPadCount @a) '0'
 
+scientificExplicitExponentSign :: FloatFormat a
+scientificExplicitExponentSign = scientific
+  { expoExplicitSign = True
+  , specials = scientificSpecialStrings
+    { positiveZero
+    , negativeZero = '-' : positiveZero
+    }
+  }
+  where
+  positiveZero = "0.0e+0"
+
 class ZeroPadCount a where zeroPadCount :: Int
 instance ZeroPadCount Float where zeroPadCount = 2
 instance ZeroPadCount Double where zeroPadCount = 3
@@ -178,7 +190,7 @@ standardSpecialStrings = scientificSpecialStrings
 --
 -- @since 0.11.2.0
 generic :: FloatFormat a
-generic = fGeneric 'e' Nothing (0,7) standardSpecialStrings False
+generic = fGeneric 'e' Nothing (0,7) standardSpecialStrings False False
 
 -- TODO: support precision argument for FGeneric and FScientific
 -- | Returns a rendered Float. Returns the \'shortest\' representation in
@@ -266,13 +278,13 @@ formatFloating :: forall a mw ew ei.
 formatFloating fmt f = case fmt of
   FGeneric {stdExpoRange = (minExpo,maxExpo), ..} -> specialsOr specials
     if e' >= minExpo && e' <= maxExpo
-       then std precision
-       else sci expoZeroPad eE
-  FScientific {..} -> specialsOr specials $ sci expoZeroPad eE
+      then std precision
+      else sci eE expoZeroPad expoExplicitSign
+  FScientific {..} -> specialsOr specials $ sci eE expoZeroPad expoExplicitSign
   FStandard {..} -> specialsOr specials $ std precision
   where
-  sci expoZeroPad eE = BP.primBounded (R.toCharsScientific @a Proxy expoZeroPad eE sign m e) ()
-  std precision = printSign f `mappend` showStandard (toWord64 m) e' precision
+  sci expoZeroPad expoExplicitSign eE = BP.primBounded (R.toCharsScientific @a Proxy expoZeroPad expoExplicitSign eE sign m e) ()
+  std precision = printSign f <> showStandard (toWord64 m) e' precision
   e' = R.toInt e + R.decimalLength m
   R.FloatingDecimal m e = toD @a mantissa expo
   (sign, mantissa, expo) = R.breakdown f

Data/ByteString/Builder/RealFloat/Internal.hs

@@ -757,6 +757,9 @@ asciiDot = ord '.'
 asciiMinus :: Int
 asciiMinus = ord '-'
 
+asciiPlus :: Int
+asciiPlus = ord '+'
+
 -- | Convert a single-digit number to the ascii ordinal e.g '1' -> 0x31
 toAscii :: Word# -> Word#
 toAscii a = a `plusWord#` word8ToWord# (asciiRaw asciiZero)
@@ -918,11 +921,17 @@ writeSign ptr True s1 =
    in (# ptr `plusAddr#` 1#, s2 #)
 writeSign ptr False s = (# ptr, s #)
 
+writeExpoSign :: Bool -> Addr# -> Bool -> State# d -> (# Addr#, State# d #)
+writeExpoSign False = writeSign
+writeExpoSign True = \ptr sign s1 ->
+  let s2 = poke ptr (asciiRaw if sign then asciiMinus else asciiPlus) s1
+  in (# ptr `plusAddr#` 1#, s2 #)
+
 -- | Returns the decimal representation of a floating point number in
 -- scientific (exponential) notation
 {-# INLINABLE toCharsScientific #-}
-{-# SPECIALIZE toCharsScientific :: Proxy Float  -> Bool -> Word8# -> Bool -> Word32 -> Int32 -> BoundedPrim () #-}
-{-# SPECIALIZE toCharsScientific :: Proxy Double -> Bool -> Word8# -> Bool -> Word64 -> Int32 -> BoundedPrim () #-}
+{-# SPECIALIZE toCharsScientific :: Proxy Float  -> Word8# -> Bool -> Bool -> Bool -> Word32 -> Int32 -> BoundedPrim () #-}
+{-# SPECIALIZE toCharsScientific :: Proxy Double -> Word8# -> Bool -> Bool -> Bool -> Word64 -> Int32 -> BoundedPrim () #-}
 toCharsScientific :: forall a mw ei.
   ( MaxEncodedLength a
   , WriteZeroPaddedExponent a
@@ -932,15 +941,16 @@ toCharsScientific :: forall a mw ei.
   , Integral ei
   , ToInt ei
   , FromInt ei
-  ) => Proxy a -> Bool -> Word8# -> Bool -> mw -> ei -> BoundedPrim ()
-toCharsScientific _ expoZeroPad eE !sign !mantissa !expo = boundedPrim (maxEncodedLength @a) $ \_ !(Ptr p0)-> do
+  ) => Proxy a -> Word8# -> Bool -> Bool -> Bool -> mw -> ei -> BoundedPrim ()
+toCharsScientific _ eE !expoZeroPad !expoExplicitSign !sign !mantissa !expo =
+  boundedPrim (maxEncodedLength @a) $ \_ !(Ptr p0)-> do
   let !olength@(I# ol) = decimalLength mantissa
       !expo' = expo + fromInt olength - 1
   IO $ \s1 ->
     let !(# p1, s2 #) = writeSign p0 sign s1
         !(# p2, s3 #) = writeMantissa p1 ol mantissa s2
         s4 = poke p2 eE s3
-        !(# p3, s5 #) = writeSign (p2 `plusAddr#` 1#) (expo' < 0) s4
+        !(# p3, s5 #) = writeExpoSign expoExplicitSign (p2 `plusAddr#` 1#) (expo' < 0) s4
         !(# p4, s6 #) = writeExponent p3 (abs expo') s5
      in (# s6, (Ptr p4) #)
   where
@@ -1018,6 +1028,7 @@ data FloatFormat a
     { eE :: Word8#
     , specials :: SpecialStrings
     , expoZeroPad :: Bool -- ^ pad the exponent with zeros
+    , expoExplicitSign :: Bool -- ^ Always prepend a + or - to the exponent
     }
   -- | standard notation with `Maybe Int` digits after the decimal
   | FStandard
@@ -1031,15 +1042,17 @@ data FloatFormat a
     , stdExpoRange :: (Int, Int)
     , specials :: SpecialStrings
     , expoZeroPad :: Bool -- ^ pad the exponent with zeros
+    , expoExplicitSign :: Bool -- ^ Always prepend a + or - to the exponent
     }
   deriving Show
-fScientific :: Char -> SpecialStrings -> Bool -> FloatFormat a
-fScientific eE specials expoZeroPad = FScientific
+fScientific :: Char -> SpecialStrings -> Bool -> Bool -> FloatFormat a
+fScientific eE specials expoZeroPad expoExplicitSign = FScientific
   { eE = asciiRaw $ ord eE
   , ..
   }
-fGeneric :: Char -> Maybe Int -> (Int, Int) -> SpecialStrings -> Bool -> FloatFormat a
-fGeneric eE precision stdExpoRange specials expoZeroPad = FGeneric
+fGeneric :: Char -> Maybe Int -> (Int, Int) -> SpecialStrings -> Bool -> Bool -> FloatFormat a
+fGeneric eE precision stdExpoRange specials expoZeroPad expoExplicitSign = FGeneric
   { eE = asciiRaw $ ord eE
   , ..
   }
+

tests/builder/Data/ByteString/Builder/Tests.hs

@@ -30,6 +30,7 @@ import           Control.Monad.Trans.Writer (WriterT, execWriterT, tell)
 import           Foreign (minusPtr)
 
 import           Data.Char (chr, isDigit)
+import           Data.Bifunctor (second)
 import           Data.Bits ((.|.), shiftL)
 import           Data.Foldable
 import           Data.Semigroup (Semigroup(..))
@@ -53,7 +54,7 @@ import           Control.Exception (evaluate)
 import           System.IO (openTempFile, hPutStr, hClose, hSetBinaryMode, hSetEncoding, utf8, hSetNewlineMode, noNewlineTranslation)
 import           Foreign (ForeignPtr, withForeignPtr, castPtr)
 import           Foreign.C.String (withCString)
-import           Numeric (showFFloat)
+import           Numeric (showFFloat, showEFloat)
 import           System.Posix.Internals (c_unlink)
 
 import           Test.Tasty (TestTree, TestName, testGroup)
@@ -761,6 +762,18 @@ testsFloating = testGroup "RealFloat"
           $  indexEnd (padLen + 1) == 'e'
           || indexEnd (padLen + 1) == '-' && indexEnd (padLen + 2) == 'e'
         ]
+    , testMatches "explict exponent sign"
+      (formatFloat (scientificExplicitExponentSign))
+      (\f -> (if abs f >= 1 || abs f == 0
+              then uncurry (<>) . second (("e+" <>) . tail) . break (== 'e')
+              else id)
+             $ showEFloat Nothing f "")
+      [ ( 0    , "0.0e+0"  )
+      , ( -0   , "-0.0e+0" )
+      , ( 1.0  , "1.0e+0"  )
+      , ( 20.0 , "2.0e+1"  )
+      , ( 0.3  , "3.0e-1"  )
+      ]
     , testMatches "f2sPowersOf10" floatDec show $
           fmap asShowRef [read ("1.0e" ++ show x) :: Float | x <- [-46..39 :: Int]]
     ]