On Sun, Oct 10, 2010 at 7:02 PM, Daniel Fischer
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