[pythran] Re: gmp

  • From: Brunet Pierrick <pierrick.brunet@xxxxxxxxxxxxxxxxxxx>
  • To: pythran@xxxxxxxxxxxxx
  • Date: Sun, 28 Oct 2012 23:24:44 +0100

Le 28/10/2012 12:49, serge Guelton a écrit :
On Sun, Oct 28, 2012 at 11:19:29AM +0100, Brunet Pierrick wrote:
Le 28/10/2012 09:27, serge Guelton a écrit :
On Sat, Oct 27, 2012 at 11:56:21PM +0200, serge Guelton wrote:
Does it mean we have to make all arguments assignable ?
The problem is not with assignable. For now, when we have a
__gmp_expr<T,G>, Assignable say : "ho, I have a specialisation which
say it is a mpz_class" but in fact, is is not really a mpz_class. It
is for exemple a __gmp_expr<mpz_struct,
gmp_binary<__gmp_expr<mpz_struct,mpz_struct>,double,binary_plus> >
or something like this.
As you can see, in fact this is the result of an addition between a
double and a mpz_class and it should be a mpf_class because we can
see a double in this expression. But it should be more complicated
otherwise gmp developper may have fix this problem isn't it?
OK I got it. Pythran cast the result to long and python to float,
because we do not try to expand the __gmp_expr...

Looking at this, it seems to solve at least a part of the issue. We
will just need to specify __gmp_binary_...<>.
For example:
__gmp_binary_op<mpz_class,double,...> type is mpf_class as here is a
double. This specification isn't in gmpxx.h AFAIK.

To use all of these features, I will first need to convert python
float to pythran mpf_class as we doesn't have big floating point
number in pythran.
In [1]: a=11111111111111111111111111L

In [2]: b=a+0.5

In [3]: b-a
Out[3]: 0.0

In [4]: type(b)
Out[4]: float

I did some work about typing today and we have a correct type management. I mean type declaration are correct for example:

mpz_class + double = double.

BUT, it doesn't really work as we can see:

#export pythran test(long)
def test(a):
    return a + 0.5

with a + 0.5, the return type is double and it is correct but (a + 0.5) result is __gmp_expr<mpz_struct [1], __gmp_binary_expr<mpz_class, double, gmp_binary_plus> > and we can't converte it to double.

I think we have two solutions:
using mpf_class as __gmp_expr<mpz_struct [1], __gmp_binary_expr<mpz_class, double, gmp_binary_plus> > can be cast to mpf_class and then convert it to double


find a solution to write a.get_d() instead of a. The result will be correct in this case as we just add 2 double value.

I thins the second one is the best one but I will wait another day before working on it.

good night.

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