Hello Benedikt,
I apologise for the late reply. I am travelling tomorrow but I will
try to get something an alpha implementation out by this Wednesday.
For now here are some preliminary answers:
On Sep 28, 2007, at 7:41 AM, Benedikt Huber wrote:
Am 18.09.2007 um 05:49 schrieb Peter Tanski:
The best solution would be to revamp the way Integer types are
implemented, so when possible they are mutable under the hood,
much like using the binary += instead of the ternary +.
Enumerations like the test in [1], below, would not be mutable
unless there were some information such as a good consumer
function that indicated the intermediate values were only
temporarily necessary.
I'm not sure if I understand this correctly;
Do you want to expose an unsafe/IO interface for destructive
Integer manipulation?
I would not expose it, just optimise it, in the same way as we can
replace recursion with loops at the Cmm level. The end result would
involve re-cycling integer memory so you might say that in some
equations integers are mutable. (If it is provable that an integer
value would not be used again, then it does not seem right not to
recycle the memory.)
The OpenSSL library is not GPL compatible, so there would be
licensing problems for GPL'd system distributions; it is also
relatively slow, though it does have a noticeably constant curve
for exponential functions.
Maybe you should add a note to
http://hackage.haskell.org/trac/ghc/wiki/ReplacingGMPNotes/
PerformanceMeasurements.
The statistics suggest that the OpenSSL BN has comparable
performance to the GMP, especially for smaller numbers.
Some note about the (very confusing) licensing issues regarding
OpenSSL would also be nice.
I will add this to the wiki. In short, paragraph 10 of the GPL and
paragraph 11 of the LGPL--here I may have the paragraphs wrong--
prohibit placing any additional restrictions on your licensees.
OpenSSL places an additional restriction on licensees: you cannot use
the name 'OpenSSL' with regard to your product, so the OpenSSL
license is incompatible with the GPL/LGPL.
[1] Simple Performance Test on (ghc-darwin-i386-6.6.1):
Malloc is fast but not nearly as fast as the RTS alloc functions;
one thing I have not started is integrating the replacement
library with GHC, mostly because the replacement library (on par
or faster than GMP) uses SIMD functions whenever possible and they
require proper alignment.
Ok, it's good to know you're already working on integrating a
(native) replacement library.
It's workable for now but I need to finish Toom3, a basic FFT, and
some specialised division operations. I also need to give Thorkil
Naur a crack at it. All of this has been on hold because I have been
too selfish and perfectionistic to give anyone what I consider a mess
and I have been working too many hours to fix it. (This seems to be
a common problem of mine; I intend to change that.)
I also performed the test with the datatype suggested by John
Meacham (using a gmp library with renamed symbols),
> data FInteger = FInteger Int# (!ForeignPtr Mpz)
but it was around 8x slower, maybe due to the ForeignPtr and FFI
overhead, or due to missing optimizations in the code.
That is quite an interesting result. Are these "safe" foreign
imports?
No. Note that `FInteger' above is even faster than the build-in
Integer type for small integers (Ints), so I was talking about
allocation of gmp integers. I elaborated the test a little, it now
shows consistent results I think [1a]; a lot of performance is lost
when doing many allocations using malloc, and even more invoking
ForeignPtr finalizers.
I found the same thing when I tried that; malloc is slow compared to
GC-based alloc. The ForeignPtr finalizers do not always run since--
as far as I know--they are only guaranteed to run before RTS shutdown.
I'm still interested in sensible solutions to Bug #311, and maybe
nevertheless simple switching to standard gmp allocation (either
with finalizers or copying limbs when entering/leaving the gmp) via
a compile flag would be the right thing for many applications.
I'm also looking forward to see the results of the replacement
library you're trying to integrate, and those of haskell Integer
implementations.
The fastest interim solution I can come up with for you would be to
use Isaac Dupree's Haskell-based integer library and set up
preprocessor defines so you could build ghc (HEAD) from source and
use that. Would that be sufficient for now?
Cheers,
Pete
[1a] Integer Allocation Test
> allocTest :: Int -> `some Integral Type T'
> allocTest iterations = (iterateT iterations INIT) where
> iterateT 0 v = v
> iterateT k v = v `seq` iterateT (k-1) (v+STEP)
- Small BigNums Allocation Test (INIT = 2^31, STEP = 10^5, k=10^6)
Results (utime samples.sort[3..7].average) on darwin-i386 (dualcore):
0.04s destructive-update C implementation
0.19s with T = Integer
0.71s non-destructive-update C implementation using malloc
with T = FInteger {-# UNPACK -#} !Int# {-# UNPACK -#} !
(ForeignPtr Mpz)
0.90s with newForeignPtr_ (no finalizer, space leak)
1.87s with Foreign.Concurrent.newForeignPtr mpz do
{ hs_mpz_clear mpz; free mpz}
1.94s with newForeignPtr free_mpz_c_impl mpz
- Small Integers Allocation Test (INIT=0,STEP=4,k=2*10^8)
Results (utime samples.sort[3..7].average) on darwin-i386 (dualcore):
0.67s for Int
2.54s for FInteger
3.62s for Integer
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