added SpecialStrings for customizing special IEEE754 float values

Data/ByteString/Builder/RealFloat.hs

@@ -62,7 +62,11 @@ module Data.ByteString.Builder.RealFloat
 
   -- * Custom formatting
   , formatFloat
+  , formatFloatSpecials
   , formatDouble
+  , formatDoubleSpecials
+  , R.SpecialStrings(..)
+  , defaultSpecialStrings
   , FloatFormat
   , standard
   , standardDefaultPrecision
@@ -161,7 +165,15 @@ data FormatMode
 -- @since 0.11.2.0
 {-# INLINABLE formatFloat #-}
 formatFloat :: FloatFormat -> Float -> Builder
-formatFloat (MkFloatFormat fmt prec) = \f ->
+formatFloat = formatFloatSpecials defaultSpecialStrings
+
+-- TODO: support precision argument for FGeneric and FScientific
+-- | Like formatFloat but allows custom strings for the special values.
+--
+-- @since ??????
+{-# INLINABLE formatFloatSpecials #-}
+formatFloatSpecials :: R.SpecialStrings -> FloatFormat -> Float -> Builder
+formatFloatSpecials ss (MkFloatFormat fmt prec) = \f ->
   let (RF.FloatingDecimal m e) = RF.f2Intermediate f
       e' = R.int32ToInt e + R.decimalLength9 m in
   case fmt of
@@ -172,13 +184,12 @@ formatFloat (MkFloatFormat fmt prec) = \f ->
           if e' >= 0 && e' <= 7
              then sign f `mappend` showStandard (R.word32ToWord64 m) e' prec
              else BP.primBounded (R.toCharsScientific (f < 0) m e) ()
-    FScientific -> RF.f2s f
+    FScientific -> RF.f2s ss f
     FStandard ->
       case specialStr f of
         Just b -> b
         Nothing -> sign f `mappend` showStandard (R.word32ToWord64 m) e' prec
 
--- TODO: support precision argument for FGeneric and FScientific
 -- | Returns a rendered Double. Returns the \'shortest\' representation in
 -- scientific notation and takes an optional precision argument in standard
 -- notation. Also see `doubleDec`.
@@ -204,7 +215,15 @@ formatFloat (MkFloatFormat fmt prec) = \f ->
 -- @since 0.11.2.0
 {-# INLINABLE formatDouble #-}
 formatDouble :: FloatFormat -> Double -> Builder
-formatDouble (MkFloatFormat fmt prec) = \f ->
+formatDouble = formatDoubleSpecials defaultSpecialStrings
+
+-- TODO: support precision argument for FGeneric and FScientific
+-- | Like formatDouble but allows custom strings for the special values.
+--
+-- @since ??????
+{-# INLINABLE formatDoubleSpecials #-}
+formatDoubleSpecials :: R.SpecialStrings -> FloatFormat -> Double -> Builder
+formatDoubleSpecials ss (MkFloatFormat fmt prec) = \f ->
   let (RD.FloatingDecimal m e) = RD.d2Intermediate f
       e' = R.int32ToInt e + R.decimalLength17 m in
   case fmt of
@@ -215,12 +234,24 @@ formatDouble (MkFloatFormat fmt prec) = \f ->
           if e' >= 0 && e' <= 7
              then sign f `mappend` showStandard m e' prec
              else BP.primBounded (R.toCharsScientific (f < 0) m e) ()
-    FScientific -> RD.d2s f
+    FScientific -> RD.d2s ss f
     FStandard ->
       case specialStr f of
         Just b -> b
         Nothing -> sign f `mappend` showStandard m e' prec
 
+-- | Standard strings for special values of IEEE754 floating point values.
+--
+-- @since ?????
+defaultSpecialStrings :: R.SpecialStrings
+defaultSpecialStrings = R.SpecialStrings
+  { R.nan = "NaN"
+  , R.positiveInfinity = "Infinity"
+  , R.negativeInfinity = "-Infinity"
+  , R.positiveZero = "0.0e0"
+  , R.negativeZero = "-0.0e0"
+  }
+
 -- | Char7 encode a 'Char'.
 {-# INLINE char7 #-}
 char7 :: Char -> Builder

Data/ByteString/Builder/RealFloat/D2S.hs

@@ -222,8 +222,8 @@ d2s' formatter specialFormatter d =
                in formatter sign m e
 
 -- | Render a Double in scientific notation
-d2s :: Double -> Builder
-d2s d = primBounded (d2s' toCharsScientific toCharsNonNumbersAndZero d) ()
+d2s :: SpecialStrings -> Double -> Builder
+d2s ss d = primBounded (d2s' toCharsScientific (toCharsNonNumbersAndZero ss) d) ()
 
 -- | Returns the decimal representation of a Double. NaN and Infinity will
 -- return `FloatingDecimal 0 0`

Data/ByteString/Builder/RealFloat/F2S.hs

@@ -202,8 +202,8 @@ f2s' formatter specialFormatter f =
                in formatter sign m e
 
 -- | Render a Float in scientific notation
-f2s :: Float -> Builder
-f2s f = primBounded (f2s' toCharsScientific toCharsNonNumbersAndZero f) ()
+f2s :: SpecialStrings -> Float -> Builder
+f2s ss f = primBounded (f2s' toCharsScientific (toCharsNonNumbersAndZero ss) f) ()
 
 -- | Returns the decimal representation of a Float. NaN and Infinity will
 -- return `FloatingDecimal 0 0`

Data/ByteString/Builder/RealFloat/Internal.hs

@@ -22,6 +22,7 @@
 module Data.ByteString.Builder.RealFloat.Internal
     ( mask
     , NonNumbersAndZero(..)
+    , SpecialStrings(..)
     , toCharsNonNumbersAndZero
     , decimalLength9
     , decimalLength17
@@ -69,6 +70,7 @@ module Data.ByteString.Builder.RealFloat.Internal
 
 import Control.Monad (foldM)
 import Data.Bits (Bits(..), FiniteBits(..))
+import Data.Bool (bool)
 import Data.ByteString.Internal (c2w)
 import Data.ByteString.Builder.Prim.Internal (BoundedPrim, boundedPrim)
 import Data.ByteString.Builder.RealFloat.TableGenerator
@@ -246,13 +248,23 @@ data NonNumbersAndZero = NonNumbersAndZero
   , mantissa_non_zero :: Bool
   }
 
+-- | Strings for special values of IEEE754 floating point values.
+--
+-- @since ?????
+data SpecialStrings = SpecialStrings
+  { nan :: String
+  , positiveInfinity :: String
+  , negativeInfinity :: String
+  , positiveZero :: String
+  , negativeZero :: String
+  } deriving Show
+
 -- | Renders NonNumbersAndZero into bounded primitive
-toCharsNonNumbersAndZero :: NonNumbersAndZero -> BoundedPrim ()
-toCharsNonNumbersAndZero NonNumbersAndZero{..}
-  | mantissa_non_zero = boundString "NaN"
-  | exponent_all_one = boundString $ signStr ++ "Infinity"
-  | otherwise = boundString $ signStr ++ "0.0e0"
-  where signStr = if negative then "-" else ""
+toCharsNonNumbersAndZero :: SpecialStrings -> NonNumbersAndZero -> BoundedPrim ()
+toCharsNonNumbersAndZero SpecialStrings{..} NonNumbersAndZero{..}
+  | mantissa_non_zero = boundString nan
+  | exponent_all_one = bool (boundString positiveInfinity) (boundString negativeInfinity) negative
+  | otherwise = bool (boundString positiveZero) (boundString negativeZero) negative
 
 -- | Part of the calculation on whether to round up the decimal representation.
 -- This is currently a constant function to match behavior in Base `show` and