Overhaul realfloat

[BebeSparkelSparkel]

#636
@clyring

[BebeSparkelSparkel]

I tested performance with ghc-9.2.7 comparing this pull with branch realfloat-bench t

Benchmark bytestring-bench: RUNNING...
All
  Data.ByteString.Builder
    Non-bounded encodings
      RealFloat
        FGeneric
          Positive
            Float (100000):                     OK
              83.8 ms ± 3.4 ms, 33% less than baseline
            Double (100000):                    OK
              59.2 ms ± 2.8 ms, 46% less than baseline
            DoubleSmall (100000):               OK
              213  ms ±  18 ms, 20% less than baseline
          Negative
            Float (100000):                     OK
              82.8 ms ± 6.7 ms, 32% less than baseline
            Double (100000):                    OK
              62.0 ms ± 4.5 ms, 42% less than baseline
            DoubleSmall (100000):               OK
              62.2 ms ± 5.6 ms, 43% less than baseline
          Special
            Float  Average (100000):            OK
              28.4 ms ± 2.2 ms,       same as baseline
            Double Average (100000):            OK
              29.4 ms ± 2.8 ms,       same as baseline
        FScientific
          Positive
            Float (100000):                     OK
              65.5 ms ± 4.5 ms, 34% less than baseline
            Double (100000):                    OK
              60.0 ms ± 3.4 ms, 41% less than baseline
            DoubleSmall (100000):               OK
              58.6 ms ± 2.8 ms, 47% less than baseline
          Negative
            Float (100000):                     OK
              65.8 ms ± 4.5 ms, 34% less than baseline
            Double (100000):                    OK
              57.0 ms ± 4.5 ms, 45% less than baseline
            DoubleSmall (100000):               OK
              61.9 ms ± 2.2 ms, 45% less than baseline
          Special
            Float  Average (100000):            OK
              29.1 ms ± 2.2 ms, 37% less than baseline
            Double Average (100000):            OK
              29.1 ms ± 2.2 ms, 29% less than baseline
        FStandard
          Positive
            without
              Float (100000):                   OK
                341  ms ±  22 ms,       same as baseline
              Double (100000):                  OK
                890  ms ±  72 ms,       same as baseline
              DoubleSmall (100000):             OK
                436  ms ±  16 ms, 11% less than baseline
            precision
              Float-Preciaion-1 (100000):       OK
                419  ms ±  22 ms,       same as baseline
              Double-Preciaion-1 (100000):      OK
                129  ms ± 7.8 ms, 28% less than baseline
              DoubleSmall-Preciaion-1 (100000): OK
                390  ms ±  13 ms, 15% less than baseline
              Float-Preciaion-6 (100000):       OK
                520  ms ±  27 ms, 10% less than baseline
              Double-Preciaion-6 (100000):      OK
                252  ms ±  13 ms, 17% less than baseline
              DoubleSmall-Preciaion-6 (100000): OK
                512  ms ±  18 ms, 12% less than baseline
          Negative
            without
              Float (100000):                   OK
                335  ms ±  13 ms, 10% less than baseline
              Double (100000):                  OK
                842  ms ±  45 ms,  9% less than baseline
              DoubleSmall (100000):             OK
                424  ms ±  22 ms, 13% less than baseline
            precision
              Float-Preciaion-1 (100000):       OK
                408  ms ±  18 ms, 10% less than baseline
              Double-Preciaion-1 (100000):      OK
                128  ms ±  11 ms, 29% less than baseline
              DoubleSmall-Preciaion-1 (100000): OK
                399  ms ±  22 ms, 12% less than baseline
              Float-Preciaion-6 (100000):       OK
                542  ms ±  54 ms,       same as baseline
              Double-Preciaion-6 (100000):      OK
                252  ms ±  18 ms, 18% less than baseline
              DoubleSmall-Preciaion-6 (100000): OK
                517  ms ±  18 ms, 10% less than baseline
          Special
            Float  Average (100000):            OK
              27.1 ms ± 2.2 ms,       same as baseline
            Double Average (100000):            OK
              29.2 ms ± 2.8 ms,       same as baseline

[clyring]

Suggested change

	import Data.ByteString.Builder.RealFloat.Internal (FloatFormat(..), fScientific, fGeneric)
	import Data.ByteString.Builder.RealFloat.Internal (positiveZero, negativeZero)
	import Data.ByteString.Builder.RealFloat.Internal (FloatFormat(..), fScientific, fGeneric, SpecialStrings(..))

Importing positiveZero and negativeZero directly by name doesn't work so well due to NoFieldSelectors/DuplicateRecordFields

[clyring]

Word8# doesn't exist until ghc-8.8, and the conversion operators were renamed in ghc-9.2, with no compatibility wrappers left behind that I could quickly find.

If you really want to track Word8#-versus-Word# in the types, I guess the necessary CPP looks like this:

#if !MIN_VERSION_base(4,13,0)
type Word8# = Word#
wordToWord8# :: Word# -> Word8#
wordToWord8# = narrow8Word#

word8ToWord# :: Word8# -> Word#
word8ToWord# x = x
#elif !MIN_VERSION_base(4,16,0)
wordToWord8# :: Word# -> Word8#
wordToWord8# = narrowWord8#

word8ToWord# :: Word8# -> Word#
word8ToWord# = extendWord8#
#endif

Or the compatibility story gets easier with boxed types, with the trade-off being that we need to make sure GHC can unbox everything for us in worker/wrapper.

[clyring]

NoFieldSelectors only exists since ghc-9.2.