cleaning up two very nasty coding habits

[Lisandro Dalcin]

On Wed, Nov 18, 2009 at 1:21 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>  When starting to code PETSc 2.0 I introduced two nasty habits
>
> 1) since we called malloc() directly and some mallocs don't like allocating
> zero length I would often allocate 1 additional space to make sure I did not
> request a zero size. Giving things like
> PetscMalloc((n+1)*sizeof(something),&something); This leads to confusing
> code because we don't know when the 1 belongs or not.
>
> 2) in order to reduce the number of mallocs I would do a single malloc for
> several variables. For example,
> PetscMalloc((n+m+1)*sizeof(PetscScalar),&buf1); buf2 = buf1 + n;
>
>  Later I changed PetscMalloc()/Free() to allow 0 length mallocs. I also
> introduced PetscMalloc2-3-4-5() to efficiently and cleanly share one malloc.
> Thus 1 and 2 became unnecessary. Since they are downright disgusting I am
> trying to eliminate 2) and would like also to reduce 1)
>
>  This fixes will likely introduce some hard to determine bugs in the near
> future (or already have). Please avoid habits 1 and 2 from now on in the
> PETSc code base.
>

I would guess that almost all the (n+1) mallocs are unnecessary,
except for "I"-like arrays associated to AIJ structures...


-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594