mpz_t C++ wrapper

[Joerg Arndt]

* Heiko Wundram <modelnine at modelnine.org> [May 01. 2008 11:27]:
> Hi all!
> 
> [...]

> 
> Anyway, quite a few temporaries can be programmatically optimized out of an 
> evaluation chain through meta-programming with templates, and I've basically 
> reimplemented mpz_class using an "optimized" expression evaluation system, so 
> that temporaries are only created when required to keep the general 
> evaluation semantics of C++ (operators bind left, assignments bind right).
> 

very nice IMHO


> Currently, I've only got my implementation of the ElGamal algorithm to 
> benchmark (which manages to execute a somewhat larger number of verifying 
> operations per second with my mpz_class re-implementation, but I'd not be 
> that hypocritical to generalize from there...), but if there's any code base 
> out there using mpz_class extensively (or someone knows of one they can point 
> me at; Google isn't especially helpful here), I'd happily give any interested 
> party access to the source so that they can test how/if my reimplementation 
> fares better for them.

Put the code on the web!


> 
> I plan on releasing the code under a BSD-style license anyway, it's just that 

At least release it also under LGPL, else the code is unlikely to
be ever part of GMP!  TG might have more comments here...


> currently (because I only use _very_ limited parts of the wrapper in my 
> application) it's probably broken in one aspect or another, and generally I 
> can't actually say that there is any speed improvement in a "real-world" 
> application of it (simply because I don't know what "real-world" terms look 
> like). It shouldn't perform worse than mpz_class, anyway (except possibly at 
> compilation speed), but I just want to escape all the NIH callers before 
> releasing it... :-)

Even if incomplete put it online (with a comment about the status).
People may well contribute if the thing is promising.


> 
> Anyway, just to give an (somewhat artificial) example:
> 
> mpz_class val, val2;
> val = val * val2 * 3 + 10 * val;
> 
> produces with my mpz_class reimplementation with g++ -O3 (transcribed from the 
> generated assembly):
> 
> mpz_init(tmp)
> mpz_mul(tmp,val,val2)
> mpz_mul_si(tmp,tmp,3)
> mpz_init(tmp2)
> mpz_mul_si(tmp2,val,10)
> mpz_add(val,tmp,tmp2)
> mpz_clear(tmp)
> mpz_clear(tmp2)
> 
> with the default mpz_class implementation with g++ -O3 (transcribed from the 
> generated assembly):
> 
> mpz_init(tmp)
> mpz_init(tmp2)
> mpz_mul(tmp2,val,val2)
> mpz_mul_si(tmp,tmp2,3)
> mpz_clear(tmp2)
> mpz_init(tmp3)
> mpz_mul_si(tmp3,val,10)
> mpz_add(val,tmp,tmp3)
> mpz_clear(tmp)
> mpz_clear(tmp3)

This indicates that your approach is a good one!


> 
> Thanks for any feedback!
> 

Hopefully TG comments some more, especially on what the priorities
to have a quality C++ wrapper are.

Btw. you may want to check out CLN.


> -- 
> Heiko Wundram


cheers,   jj