[Haskell-cafe] Re: RealFrac methods for Double and Float
Antoine Latter
aslatter at gmail.com
Sun Oct 10 22:44:24 EDT 2010
On Sun, Oct 10, 2010 at 7:02 PM, Daniel Fischer
<daniel.is.fischer at web.de> wrote:
> Greetings,
>
> I have put together a package to test possible implementations of the
> RealFrac methods for Double and Float (base-2 IEEE754) and uploaded a
> .tar.gz bundle to http://hackage.haskell.org/trac/ghc/ticket/2271 .
>
> On the one hand, pure Haskell implementations, on the other hand
> implementations calling out to rint[f], trunc[f], floor[f] and ceil[f] from
> math.h.
>
> Both ways go via Integer by default, with a specialised faster
> implementation for Int (and narrower types, but those RULES haven't yet
> been written) enabled by a rewrite rule.
>
> Overall, the pure Haskell implementations don't fare badly on my computer.
> All give a speedup compared to the current implementation, for most
> conversions, pure Haskell is on par with or faster than the C-call
> (although that would probably change if the C functions were made primops).
>
> The FFI calls are significantly faster for
> properFraction :: Double -> (Integer, Double)
> and for round (except round :: Integral a => Float -> a when compiled
> via C, then native and FFI are on par).
>
> Sample results for the speedups against the current implementation (note:
> for truncate :: x -> Int, the Prelude value is fst . properFraction, not
> the rewritten float2Int or double2Int) are included in the tarball.
>
> I would appreciate feedback from your tests/benchmarks on other platforms,
> especially 64-bit platforms (mine is x86 linux, 32 bit).
>
> To run the QuickCheck tests, you need QuickCheck-2.*, to run the
> benchmarks, criterion.
>
> More instructions in the README.
>
> Thanks,
> Daniel
>
I have results from my Intel-based MacBook, 64-bits, GHC 7 rc. The
quickchecks failed to run:
QuickChecking Double
properFraction/Int
qcDouble: qcDouble.hs:(10,10)-(15,5): Missing field in record
construction Test.QuickCheck.Test.chatty
QuickChecking Float
properFraction/Int
qcFloat: qcFloat.hs:(10,10)-(15,5): Missing field in record
construction Test.QuickCheck.Test.chatty
This is with QuickCheck 2.3.0.2.
Take care,
Antoine
$ sh bench.sh
Results from ncgDouble:
Relations for properFraction:
Prelude 1.000000
C via Integer 2.429916
Hs via Integer 1.904705
C Int 17.251877
Hs Int 28.596726
Relations for truncate:
Prelude 1.000000
C via Integer 3.743818
Hs via Integer 3.535077
C Int 15.390511
Hs Int 25.461061
Relations for floor:
Prelude 1.000000
C via Integer 3.853145
Hs via Integer 4.790661
C Int 14.547410
Hs Int 15.272021
Relations for ceiling:
Prelude 1.000000
C via Integer 4.234731
Hs via Integer 2.934738
C Int 14.128199
Hs Int 15.183423
Relations for round:
Prelude 1.000000
C via Integer 4.380557
Hs via Integer 1.836171
C Int 27.479207
Hs Int 9.352543
Results from viaCDouble:
Relations for properFraction:
Prelude 1.000000
C via Integer 2.424372
Hs via Integer 1.899951
C Int 17.387781
Hs Int 28.502385
Relations for truncate:
Prelude 1.000000
C via Integer 3.735578
Hs via Integer 3.533399
C Int 15.513855
Hs Int 25.389048
Relations for floor:
Prelude 1.000000
C via Integer 3.844556
Hs via Integer 4.793321
C Int 14.418142
Hs Int 15.235541
Relations for ceiling:
Prelude 1.000000
C via Integer 4.238978
Hs via Integer 2.939887
C Int 14.255595
Hs Int 15.012826
Relations for round:
Prelude 1.000000
C via Integer 4.375220
Hs via Integer 1.832638
C Int 27.413318
Hs Int 9.386865
Results from ncgFloat:
Relations for properFraction:
Prelude 1.000000
C via Integer 0.333999
Hs via Integer 0.499852
C Int 4.417461
Hs Int 4.558648
Relations for truncate:
Prelude 1.000000
C via Integer 0.496294
Hs via Integer 0.525865
C Int 4.311807
Hs Int 4.556461
Relations for floor:
Prelude 1.000000
C via Integer 0.519939
Hs via Integer 0.558956
C Int 4.611193
Hs Int 4.154393
Relations for ceiling:
Prelude 1.000000
C via Integer 0.532954
Hs via Integer 0.572631
C Int 4.608487
Hs Int 4.234378
Relations for round:
Prelude 1.000000
C via Integer 0.618715
Hs via Integer 0.575423
C Int 5.438467
Hs Int 3.705514
Results from viaCFloat:
Relations for properFraction:
Prelude 1.000000
C via Integer 0.334372
Hs via Integer 0.500771
C Int 4.479688
Hs Int 4.716925
Relations for truncate:
Prelude 1.000000
C via Integer 0.499481
Hs via Integer 0.529176
C Int 4.343629
Hs Int 4.589870
Relations for floor:
Prelude 1.000000
C via Integer 0.520805
Hs via Integer 0.559927
C Int 4.631558
Hs Int 4.216547
Relations for ceiling:
Prelude 1.000000
C via Integer 0.532622
Hs via Integer 0.574791
C Int 4.635416
Hs Int 4.266135
Relations for round:
Prelude 1.000000
C via Integer 0.619787
Hs via Integer 0.577242
C Int 5.477356
Hs Int 3.731998
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