On 2014-10-16, Dima Pasechnik <[email protected]> wrote:
> On 2014-10-16, Volker Braun <[email protected]> wrote:
>> C99 VLA are not dynamically allocated, they exhaust the static stack rather
>> quickly. If you are writing the C part of the code yourself it is in the
>> long run almost certainly better to put matrices on the heap. If you have a
>> maximal size for arrays you could use that as static bound. Or replace them
>> with a C++ matrix class that does the dynamic allocation (e.g.
>> boost::numeric::ublas::matrix)
>
> it's something I wrote 20+ years ago, and uses a lot of a[i][j] syntax.
> Allocation was done statically. So I changed it to VLAs, but I wouldn't
> want to spend more time on it.
>
> It's not 100% clear how to use heap instead.
> Apparently I can call a function
>
> void f(int n, int a[][n]){...}
>
> by doing (instead of `int b[n][n]; f(n,b);`)
>
> int *b;
> b=(int *)malloc(n*n*sizeof(int));
> f(n, b);
>
> but this gives scary warnings about types:
>
> warning: passing argument 2 of ‘f’ from incompatible pointer type [enabled
> by default]
> note: expected ‘int (*)[(sizetype)(n)]’ but argument is of type ‘int *’
never mind, I just realised that I can do
f(n, (int (*)[])b);
to do away with the warning.
>
> even though the code appears to be working.
I still have to see a guarantee that formal parameters like in f are always
implemented
so that this trick works.
>
>
>>
>>
>>
>>
>> On Thursday, October 16, 2014 12:28:21 PM UTC+1, Dima Pasechnik wrote:
>>>
>>> In C99 it's possible to do dynamic allocation of multidimensional arrays:
>>>
>>> void blah(int n) {
>>> int a[n][n];
>>> ...}
>>>
>>> but this does not seem to be supported in Cython. If I try
>>> sage -cython on
>>>
>>> def t(int n):
>>> cdef int a[n][n]
>>> cdef int i, j
>>> for i in range(n):
>>> for j in range(n):
>>> a[i][j]=i+j
>>> return a[0][n-1]
>>>
>>> I get
>>>
>>> Error compiling Cython file:
>>> ------------------------------------------------------------
>>> ...
>>> def t(int n):
>>> cdef int i, j
>>> cdef int a[n][n]
>>> ^
>>> ------------------------------------------------------------
>>>
>>> m.pyx:3:18: Not allowed in a constant expression
>>>
>>> As I have C99 code I'd like to hook up to Sage, I'd really
>>> like to know how to get around this limitation (with as little overhead
>>> as possible)
>>>
>>> Thanks,
>>> Dima
>>>
>>>
>>>
>>
>
--
You received this message because you are subscribed to the Google Groups
"sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-devel.
For more options, visit https://groups.google.com/d/optout.
