Here the allocated size is fixed (always 64 pointers), so alloca does
not seem needed.
I wonder how many other functions could avoid dynamic allocation
like this one (either with a stack array or alloca).
Regards
Dominique
On Mon, Oct 7, 2019 at 10:26 PM Mateusz Wajchęprzełóż
<mati271...@gmail.com> wrote:
>
> What about sqlite3StackAllocZero and SQLITE_USE_ALLOCA?
>
> pon., 7 paź 2019 o 20:51 Dominique Pellé <dominique.pe...@gmail.com>
> napisał(a):
>
> > Hi
> >
> > Below is a patch which avoids a dynamic
> > allocation in vdbeSorterSort(...), using a local
> > stack array instead (faster and smaller code).
> > I assume that a local array of 64 pointers is small
> > enough to be in the stack.
> >
> > Is this worth merging?
> >
> > $ fossil diff src/vdbesort.c
> > Index: src/vdbesort.c
> > ==================================================================
> > --- src/vdbesort.c
> > +++ src/vdbesort.c
> > @@ -1394,25 +1394,20 @@
> > ** SQLITE_OK if successful, or an SQLite error code (i.e. SQLITE_NOMEM) if
> > ** an error occurs.
> > */
> > static int vdbeSorterSort(SortSubtask *pTask, SorterList *pList){
> > int i;
> > - SorterRecord **aSlot;
> > + SorterRecord *aSlot[64] = { 0 };
> > SorterRecord *p;
> > int rc;
> >
> > rc = vdbeSortAllocUnpacked(pTask);
> > if( rc!=SQLITE_OK ) return rc;
> >
> > p = pList->pList;
> > pTask->xCompare = vdbeSorterGetCompare(pTask->pSorter);
> >
> > - aSlot = (SorterRecord **)sqlite3MallocZero(64 * sizeof(SorterRecord *));
> > - if( !aSlot ){
> > - return SQLITE_NOMEM_BKPT;
> > - }
> > -
> > while( p ){
> > SorterRecord *pNext;
> > if( pList->aMemory ){
> > if( (u8*)p==pList->aMemory ){
> > pNext = 0;
> > @@ -1438,11 +1433,10 @@
> > if( aSlot[i]==0 ) continue;
> > p = p ? vdbeSorterMerge(pTask, p, aSlot[i]) : aSlot[i];
> > }
> > pList->pList = p;
> >
> > - sqlite3_free(aSlot);
> > assert( pTask->pUnpacked->errCode==SQLITE_OK
> > || pTask->pUnpacked->errCode==SQLITE_NOMEM
> > );
> > return pTask->pUnpacked->errCode;
> > }
> >
> > Regards
> > Dominique
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> >
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